Compartment Firefighting Strategy & Tactics
Updated 25 May 2000
VALENCIA,
SPAIN - May 1993
As we crawled into the room the fire's roar was somewhat disconcerting.
The thick smoke from the fire's plume was banking down setting an 'interface' at
about 1.5 metres from floor level and the heat radiating downwards from the
ceiling could clearly be felt through the substantial layers of our protective
clothing. I looked directly above our position, into the darkness of the smoke,
and noted some yellow tongues of flame rolling the ceiling, detaching themselves
from the main body of fire that blazed in the furthest corner of the
compartment. We had advanced about 1.5 metres into the room as I reached for the
nozzle of the high-pressure hosereel line and discharged the briefest
'pulsation' of water-fog into the upper strata above our heads. There was no
drop-back in terms of water particles and the series of 'popping' sounds
suggested that the fog was 'doing its thing' in the super-heated gas layers. The
tongues of flame dispersed for a few brief seconds before resuming their eerie
'snake-like' dance towards the open access point (doorway) situated behind us.
"Hold the water" shouted Miguel over the BA comm's radio. As we inched
further into the room I realised then that I was placing my deepest trust in the
man.
The smoke continued to bank down around us and I watched in awe as
several 'balloon-like' pockets of fire gases ignited, each for a brief second,
in front of my eyes about one metre from the floor. I could sense the moment of
compartmental 'flashover' was fast approaching and I instinctively reached for
the nozzle again. "WAIT", shouted Miguel - he laughed as he reached
back and kicked the access door almost shut. I felt extremely vulnerable but
then, as if turned off by a tap, the fire suddenly lost its 'roar'
and the rolling flames in the plume above dispersed completely.
Everything went dark as the fire 'crackled' and the smoke banked right down to
the floor. There was an eerie silence within this blinding experience that
seemed all too familiar to the 'firefighter' in me. Miguel took the nozzle out
of my hands and discharged several brief 'pulsations' of water-fog, on a wide
setting, into the upper portions of the room. Again, there was no 'drop-back'
and you could almost sense the minute particles of water suspending themselves
within the super-heated flammable gas layers. The steam 'over-pressure' and
humidity was negligible and any air movement went unnoticed. More importantly,
the thermal radiation from above had lessened considerably reducing the
likelihood of a flashover. Then I heard Miguel's voice over the comm's calling
for an exterior tactical venting action and almost instantly the smoke layer
began to rise as firefighters in the street vented the window serving the room.
The fire in the corner of the room became visibly active again as it increased
in intensity, however this time the tongues of flame in the ceiling layer were
heading towards the open window and away
from our position.
Miguel Basset was the Chief Fire Officer of the Valencia (County) Fire
Brigade in Spain. He was a practical man who had learned much about fire and its
behaviour under various conditions. He had 'played' with fire over a number of
years, experimenting alongside his trusty team
of firefighters, pushing ventilation parameters to their limits in an attempt at
gauging their effect on fire growth. Within the fiery depths of this derelict
house training situation Miguel taught me a great deal about asserting control
over the fire. He had demonstrated quite clearly how firefighters may utilise tactical
venting actions to attack
a fire's progress and that simply by closing the access door or opening a window
at its highest level you can avert or delay a backdraught or flashover
situation. He also showed how firefighters can reduce thermal radiation from
above by reversing the direction of a fire's plume away from the access
point, as described.
My fireground experiences were gained over a 25 year period, working at
extremely close quarters alongside Swedish, Spanish, Dutch and North American
firefighters. I served out of some of the world's busiest
fire stations in both the UK and abroad and grasped at every opportunity
to share this experience with colleagues. Following publication of my 1992 book Fog
Attack, several reviews decribed my approach as 'somewhat
controversial'. I was accused of challenging the status quo and many
traditionalists refused to acknowledge my views on certain strategic
applications in relation to the tactical venting of fire involved structures;
the use of fans to provide positive pressure ventilation (PPV) in both a
defensive and an offensive mode; and the Swedish approach of
discharging brief 'pulses' of water-fog into the upper layers of
super-heated gases that so often threaten to engulf advancing firefighters in
flames as they ignite with explosive force. I spent much time and effort!trying
to encourage a general 'awareness' and
appreciation of the potential for fire gas layers to ignite and strived to
inform just under what circumstances this was likely to happen. These topics
were of great interest to me and I considered
there was a genuine quest for knowledge in all areas of both a practical
and scientific nature coupled with a strong need for further research. It was
therefore pleasing to me when the Home Office Fire Research & Development
Group (FRDG) finally commissioned studies in 1994 that encompassed such aspects
of structural fire control. The studies culminated in lengthy reports and
generally approved the basic strategy for compartmental firefighting as had been
detailed in my earlier works from 1979 on.
In 1997 the Home Office published an update of the Fire Service Manual in
the form of Volume 2 - Fire Service Operations (Compartment Fires and Tactical
Ventilation). The content of
this timely publication was strongly influenced by the earlier FRDG
reports and
gave general coverage to the four areas I had personally researched
and reported on during the twenty year period prior; namely: (1) tactical ventilation
(a term with definition I had first introduced
in 1991 and a strategy I had reported
on frequently since an early article in 1985); (2)
Positive Pressure Ventilation
( a technique that was still in its infancy when my original article appeared in
1991); (3)
back-draughts and flashovers ( it was also in 1991 that I embarked upon
a series of articles to increase awareness and improve the understanding of such
hazards amongst firefighters although I had originally questioned the knowledge
base in 1985); (4)
water-fog applications
(the manual touches briefly upon the Swedish three dimensional water fog
applications - termed 'offensive firefighting' - a topic I had researched and
reported on extensively following
my initial article in 1992). These were all areas of firefighting strategy that
I had introduced and reported upon to the British fire service through the pages
of our national journals in an attempt to draw debate and create interest. The
updated manual was welcomed as an important addition to the series and what had
previously occupied a paragraph consisting of 73 words in an earlier edition,
advising firefighters that ventilation operations were only to be utilised as a
'last resort' , now filled a complete self-contained manual emphasising
important aspects of compartmental fire control that surely concerned every
operational firefighter. The publication was typically well laid out and
illustrated and offered clear if concise advice. Whilst being far from the
complete works one feels it was never intended to offer more than a fleeting
glance at topics that have fuelled so much debate during the past two decades.
However, I would have hoped for a more detailed bibliography to refer students
onwards in their quest for knowledge concerning all aspects of compartmental
firefighting.
In February 1996 a fire occurred in Blaina, Gwent, where two firefighters
tragically lost their lives during a rescue attempt when a 'backdraught' erupted
throughout the building in which they were working. The subsequent HSE
investigation led to the issue of improvement notices suggesting deficiencies in
training and a lack of awareness
of fire growth and development amongst the firefighters on scene contributed to
such a tragic outcome. Whilst these notices were issued to Gwent Fire Service,
they were intended for all of us! All of a sudden, 'realistic hot-fire training'
and thoeretical 'awareness' training in fire growth and development were the
order of the day - but why should it take the loss of two firefighters to create
such inertia?! Perhaps I hadn't been effectively forceful or controversial enough
during the past few years! Despite the minority of authorities who had opted to
run some sort of 'hot-fire' training, there remained a great deal to be done if
we were to prevent another 'Blaina'. There had been similar tragedies before but
the circumstances that prevailed during the early hours on this cold february
morning were particularly shocking
BLAINA,
GWENT - 1st February 1996.
The first of eight calls to a fire initially involving the ground floor
of a two-storey terraced house in Blaina was received at 0603 hours. A single
fire appliance, with a retained crew of six, was mobilised to the property which
was categorised in a class 'C' risk area. However, the predetermined attendance
was upgraded to two pumping appliances on receipt of a further call which stated
that children were still inside the property.
The first appliance to arrive was confronted with a heavily smoke-logged
house with no signs of fire visible. A team of two firefighters wearing
breathing apparatus immediately entered the property and proceeded upstairs
where they located and rescued a young child. On re-entering the property to
continue their search the two firefighters were caught in a 'backdraught' which
engulfed the whole house in flames (0615 hours). Both firefighters remained
trapped and died from their injuries.
SEQUENCE
OF EVENTS
0548
Occupier discovered fire in ground floor kitchen at
rear of premises.
0600E
Entire building smoke-logged despite containment in
kitchen.
0603
Initial call received by brigade from next door
neighbour.
0604
First appliance despatched by control.
0605E
Kitchen window failed.
0606
2nd call to brigade.
0608
First appliance mobile to incident.
0609
3rd call to brigade reports 'children still inside property'.
0610
Second appliance despatched by control.
0610
First appliance arrives on scene.
0611
Ist crew of two firefighters wearing BA enter property
at front with hosereel.
0611
Assistance and informative messages sent.
0612
Unsuccessful attempt by firefighter to run 2nd hosereel
around property to rear.
0613
1st BA crew out of property with one child found.
0615E
Fire breaks through kitchen ceiling to first floor.
0615
1st BA crew return inside to locate second child
reported missing.
0615
Backdraught occurs engulfing entire house in flames on
both ground
and first floors.
0617
2nd BA crew enter property in attempt to rescue
colleagues trapped inside.
0619
Second appliance arrives on scene - 5 further
firefighters.
0620
One line of hose run from hydrant to augment tank
supply of pump in use.
0620
3rd BA crew enter property to assist rescue of trapped
firefighters.
0625
3rd BA crew exit and re-enter to advance a 45mm
hoseline into
ground floor area.
0627
1st firefighter removed from ground floor to street .
0629
2nd firefighter removed from ground floor to street.
'E'
- Time as estimated by scientific advisors to the investigation.
THE
BLAINA INCIDENT AS A CASE STUDY.
Whilst the Health & Safety Executive recognised certain deficiencies
as being major contributing factors to the tragic outcome of this incident,
their inclusion in the issue of improvement notices were isolated, as there were
in fact several tactical considerations that
needed redressing if real lessons
were to be drawn from the experience. Similarly, the 1997 update of the manual
of firemanship (compartment fires) failed
to take such an opportunity and in reality, the circumstances that prevailed at
Blaina are still likely to occur over and again, perhaps in your very own
community in the not too distant future! The
point is, I am far from convinced that our firefighters are fully prepared for
another 'Blaina'. I certainly don't believe that our fireground philosophy is
effectively advanced or proactive enough and I feel that our tactical approach
is strongly susceptive to traditionalist influence - we are still'
'reactive' in our approach.
The objective of any firefighting operation is surely 'containment'. The
restriction of fire spread and the protection of exposures are major factors in
terms of fire control and a fire will only remain compartmental until a natural
opening is available in the boundary or an element of structure is breached by
the flames. In terms of property conservation the ideal of containment is
obvious. However, its relevance in the context of firefighter 'awareness''
is that once a fire progresses beyond the compartment of origin, to become 'structural' (as was the
case in Blaina), the potential for backdraught increases greatly. So, if our
overall objective is 'containment' exactly what factors, applications and
options should we be looking at, as on-scene firefighters,
that might influence our strategic approach? I would list them as follows
-
1.
Capability (manpower, equipment, water supply).
2.
Awareness.
3.
Reaction Time.
4.
Search & Rescue Time.
5.
Tactical Ventilation & Air Control.
6.
Water Applications.
7.
Training.
Take time to review the seven factors above and evaluate your own
brigade's approach under similar circumstances. To do this requires a complete
philosophical analysis of your fireground strategy - is it structured and planned?
If you were the OIC at such an incident what would be your primary
objectives? - Rescue? Ventilation? Firefighting?; and, would such a decision be
based on personal opinion or is your brigade's approach effectively proactive
in having incorporated such ethical decision making into a carefully structured programme of fireground strategy. If
left to formulate their own decisions on such matters fireground officers will
inevitably provide variable outcomes - some of these may prove controversial
whilst others may not be effectively risk
analysed.
In 'Fog Attack' in 1992 I listed thirteen points under 'Primary'
and 'Secondary' actions to be taken by firefighters on arrival at a building
fire. This list is comprehensive in that it provides a 'risk-analysed' structure
of fireground strategy that is effective, safe and universal to all occupied
building types. I called this the ''Fireground
Action Plan' which is modular
in its approach, assigning firefighters to one of four units - (a) Attack Team;
(b) Support!Team; (c) Peripheral team; and (d) Roof Team. It is a simple plan
that functions equally well with any pre-determined attendance of variable size
or capability.
The source of reference should be reviewed for a deeper understanding but
the overall plan lists Primary and Secondary actions as follows -
Primary
Actions.
Secondary Actions.
(1) Position apparatus.
(1) Interior search plan.
(2) Visible Rescues
(exterior).
(2) Tactical Ventilation
(3) Initial water supply.
(3) Additional water supply
(4) Cover hoselines.
(4) Interior lighting.
(5) Exterior lighting.
(5) Master Streams.
(6) Forcible entry
(exterior)
(6) Fixed installations.
(7) Fire attack.
The plan is described as 'comprehensive but by no means complete'. It
also remains flexible in as much as 'tactical
options' may be either up or down-graded in the hierarchy to suit specific
circumstances - but a sound basis of risk analysis must be put forward to
support!any such decisions. For example, the Secondary action of 'tactical
ventilation' may be upgraded to a Primary action with good reason; for
example, where strong 'backdraft' indicators are preceding entry to a
compartment an exterior tactical venting action may be upgraded in front of
'fire attack' (and entry) as a safer option. Also, note the grading of
'interior search'' as a
secondary action. This view I put forward in 1991 appeared controversial at the
time but is now finding support
amongst a growing number of fire
officers. John Mittendorf, a retired Los Angeles fire chief,
clearly made the point in the 1994 FRDG report!on tactical ventilation
where he claimed that the priority between fire attack and search & rescue
was changing and that controlling the atmosphere and conditions within the
structure was increasingly being viewed as
the primary action before carrying out search & rescue
operations. He suggested that search & rescue times may be reduced
where smoke is removed from the structure by tactically venting and went on to
criticise the New York firefighting philosophy which prioritizes search &
rescue operations over fire attack. It should be remembered, any
tactical venting action must be preceded by carefully sited 'cover'
hoselines and the plan recognises this important point.
In my opening (author's) notes in 'Fog
Attack' I placed great emphasis on what I consider to be the most important
point in the book where the reader is urged to examine the text carefully. 'It
is often only with hindsight, following a
personal experience, that important points (in the book) become
highly relevant. The experience
of others is here' - to be learned! The 'fireground action plan' is
uniquely simple and its strengths go way beyond that of compartmental
firefighting. However,even in its most basic form, I only wish the crews at
Blaina had resorted to it - a more positive outcome might have resulted and a
tragedy may have been averted.
Seven
Point Review.
1.
Capability (Manpower, equipment & water supply).
In 'Fog Attack' an entire
chapter was devoted to 'force deployment' where a detailed analysis was made of
'capability' factors associated with several fire brigades around the world. The
brigades were mainly city based and demonstrated initial responses varying from
nine to fiftyseven firefighters and three to twelve fire appliances on the first
call to a fire in their area, with an average pumper crew consisting of four
firefighters. In suburban and rural districts it was extremely common to find
'volunteer' forces providing fire cover and in some cases an initial response to
'fire' resulted in a substantial turn-out in terms of appliances and equipment,
although this was sometimes affected by the time of day.
In Blaina the response was minimal but conformed to the UK system of
'categorisation' based upon risk analysis. However, an initial response of six
firefighters is, in my opinion, severely stretched at the outset of any working
structural fire where the constraints of firefighter 'accountability' are of
major concern. I have always voiced strong feelings that at any structural fire
the initial response (as a minimum) must comprise of an OIC (Officer), a Pump
Operator/Driver, and two
crews, each of two firefighters, rigged in breathing apparatus. Obviously
prioritizing any exterior rescue situation on arrival, the first crew is
responsible for advancing an initial attack on the fire whilst the second crew
fulfill one, or more, of the following requirements - (a) tactical venting; (b)
back-up hoseline (maybe of larger capacity than the first line in); and/or (c)
search & rescue. It is essential
to be able to provide these options on the initial attendance with the safety of
personnel in mind.
It then becomes obvious that BA Control duties must be undertaken by
either the OIC or pump-operator on an initial response of six firefighters. This
is somewhat in conflict with 'safe-practice' and ideally a seventh firefighter
is needed to fulfill the role (yes - I am aware of constraints on appliance
seating!). However, the concept of having four firefighters wearing BA on an initial response to a working
structural fire is an essential feature of the fireground action plan and it is my opinion that this action should
counteract the option of assigning a firefighter specifically to undertake BA
Control duties in isolation unless the first-arriving crew consists of seven or
more. Even under those circumstances no hard and fast rule should prevent the
OIC from utilising a seventh
firefighter for any specific role that would serve to increase the effectiveness
and safety of the firefighting and rescue operation. This is strategy
in action!
Also in Fog Attack there are
references to optimal use of water
supplies but a critique of the Blaina incident in such terms is irrelevant.
The review on equipment (nozzles) is
discussed later in the paper.
2.
Awareness.
Throughout Fog Attack and most
of my work you will observe the word 'awareness''
is used frequently. I was very conscious that this most important 'inner sense'
was often sadly lacking amongst firefighting colleagues. This is partly due to
educational/training factors but it goes further than that. To be aware
or possess awareness and the necessary forethought that is required to have such is an attribute. Just as some
top sporting stars are able to demonstrate awareness on the field of play, so
too are some firefighters more 'aware' than others! It is an essential attribute
of a good leader but sadly, many
officers are also lacking. By definition awareness means conscious, watchful, and vigilant, demonstrating effective powers of
observation and an understanding of relevant matters. Quite simply, training and
education can dramatically increase awareness and the HSE gave recognition to
these important aspects through the improvement notices issued in Gwent. The
firefighters in Blaina were obviously aware that they were entering a hazardous
environment but perhaps they weren't fully appreciative of the actions that
might have been taken to alleviate a worsening situation. I presume they had
access to recent literature in the form of a manual update concerning
compartment fires, but then its one thing reading about backdraughts and
flashovers and another to actually appreciate
the dangers. This appreciation often only comes through real-life experience or realistic
training simulations although an understanding of the basic theory provides
a sound framework upon which the practical training may be structured.
The growth and development of compartmental fires is a subject that has
often led to inaccurate research and theory.This has led to a wide range of
terms and definitions used to describe certain events that only serve to confuse
the issue. The conditions that result in 'flashover' and 'backdraught' are often so closely inter-linked that
on-scene firefighters are sometimes uncertain as to what event actually took
place and therefore use the term flashover
as a general description for sudden escalations in fire growth and development.
The new manual updates have gone some way to clarify terms and definitions but
even here the issue remains partially confusing.
'BACKDRAUGHT'
- 'Limited ventilation can lead to a fire in a compartment producing fire gases
containing significant proportions of partial combustion products and unburnt
pyrolysis products. If these accumulate then the admission of air when an
opening is made to the compartment can lead to a sudden deflagration. This
deflagration moving through the compartment and out of the opening is a
backdraught'.
The manual states 'There are two possible backdraught scenarios' on page
seven but actually goes on to describe several events - (some of which don,t
conform to the standard definition for 'backdraught').
However, the intention is to simplify the theory, and quite rightly so,
as it is important for the
firefighter not to get too entwined in the complexities. At the same time, it is
essential that firefighters recognise both, the different circumstances under
which fire gas ignitions are likely to
occur, and the'actions' or events
likely to initiate such deflagrations.
For the sake of continuity I will group fire gas ignitions
associated with the term backdraught
as follows -
1.
The ignition of a pre-mixed volume of flammable volatiles (fire gases/smoke)
that have accumulated within the compartment of origin or beneath a horizontal
barrier, or a ceiling, or within a roof space, structural void or adjacent
compartment. Such ignition may occur during the fire's development or some time
following its extinction. The addition of further quantities of air is not
a necessary requirement for such an ignition to occur.
2.
The increase in flame volume when an under-ventilated fire suddenly gets an
additional supply of air. This event may be brought about by any breach of the
fire compartment boundary, ie; broken window; open access door etc, or by a
sudden gust of wind or air through an existing opening. The effect may be to
increase the burn-rate, causing a flame front to roll 'lazily' across the
ceiling. Alternatively, the effect may be explosive. This is the 'classic' backdraught
situation.
3.
The auto ignition of super-heated unburnt volatiles (in smoke) at the point
where they exit from a compartment to mix with air. This event may occur either
inside the structure or externally and the ignition is likely to burn back
through the gases into the compartment from whence they came. This effect, also
termed 'flashback', may establish a
diffusion flame of air burning in fuel, rather than the other way around.
The above paragraphs do not propose to lay foundation for scientific
definition but merely demonstrate the variable circumstances associated with the
term (and accepted definition) of backdraught.
It now becomes obvious that ignition of the fire gas layers may occur at any
stage of operations including the 'turning over & damping down' phase
following extinguishment. Such an ignition may result in fast (explosive) or
slow (rolling) combustion. It may occur within the compartment of origin, or in
adjacent compartments, spaces, or voids, or at the point of entry/exit,or at
ventilation points as firefighters tactically vent super-heated gases. Any such
ignition may create flames from floor to ceiling or possibly just at high level
within the compartment. The dangers exist at all stages from opening
&entering, or whilst occupying
space, to after the fire is out!
The key lies in being AWARE of all
these facts and appreciating the
potential for such events.
The firefighter must also possess an awareness of the
circumstances likely to initiate such ignitions of the fire gas layers. This is simple and easy to
learn in list form -
1. Opening & entry at
the access points is going to feed the fire with massive amounts of air!
2. Tactical ventilation of
windows may provide enough air in-flow to cause a backdraught.
3. The breakage of windows
caused by heat from the fire will do the same.
4. The breaching of a
compartment boundary (elements of structure) by the fire will introduce
ignition
sources to adjacent areas that may have accumulated flammable gas layers them-
selves.
5. The 'turning over' or
disturbing of hidden pockets of fire may release ignition sources into
accumulated
flammable gas layers.
6. The sudden inflow of air
through an existing opening, caused by wind gusts or ppv fans,
may cause
an ignition or dramatically increase the rate of burning within a compartment.
Signs
and Symptoms of Backdraughts.
The manual update is extremely conservative in listing backdraught
indicators and list four signs of an impending fire
gas ignition -
1. Dense smoke with no
obvious signs of flame.
2. Smoke blackened windows.
3. Smoke 'pulsing' from
doors and windows.
4. Signs of heat around the
door.
Fog
Attack lists
several more signs that I consider reliable 'indicators' -
5. Thick 'rolling' black
smoke issuing from a compartment opening may give moments warning.
6. Smoke may force its way
out around closed windows, doors and from under the eaves.
7. Windows may be 'rattling'
and too hot to touch.
8. Smoke may appear to
'suck' back into the structure.
9. The appearance of blue
flames at any stage may be considered a reliable indicator.
10. Confined fires, such as in basements and roof spaces are more likely
to initiate backdraft.
11. A sensation of 'air' rushing past your ears towards the fire
(swirling smoke) suggests it
''FLASHOVER'
- In a compartment fire there can come a stage where the total thermal radiation
from the fire plume, hot gases and hot compartment boundaries causes the
generation of flammable products of pyrolysis from all exposed combustible
surfaces within the compartment. Given a source of ignition, this will result in
the sudden and sustained transition of a growing fire to a fully developed fire.
This is called 'flashover'.
For a flashover to occur the
rate of heat release inside the compartment must exceed, and partially maintain,
a critical level which is sufficient to provide the heat flux necessary for such
an event to take place. This critical rate of heat release depend on a number of
factors, including the rate of heat loss through the compartment boundary; the
rate of air flow into the compartment through any ventilation openings; and the
dimensions of the compartment itself. Various studies have attempted to produce
a reliable formula for estimating the amount of HRR necessary to achieve flashover
in a compartment fire but there are so many variables involved and this has yet
to be realised. However, there are various estimates in current circulation
suggesting HRRs of 0.5 - 1 MW as being
the minimum necessary for achieving flashover
in the 'average' size compartment, although this estimate is subject to
changes where, for example, interior wall linings or positioning of 'item of
origin' may either reduce or increase such predictions. Where expanded
polystyrene is used as a wall lining flashover
may be achieved with a HRR as low as 200 KW.
The FRDG report!examined sudden changes in the heat release rate of a
fire in an enclosure and specified seven ways in which a sudden change may
occur. Four of these are quoted as step
events representing transitions between fuel and ventilation controlled
states and the remaining three are transient
events corresponding to one of the components of the fire triangle
(oxygen, heat or fuel) suddenly becoming available. Whilst backdraught
is termed as a transient event in
terms of fire development where the heat release rate is not sustained as the gases burn off rapidly, flashover is termed as
a step event where the combustion
process is sustained. The report!also
demonstrated that flashover as a step
event may also occur as a result of increased
ventilation. This point is not mentioned in the definition and it can
clearly be seen how firefighters sometimes confuse the terms flashover/backdraught
and are often unable to
differentiate on an 'event'. The Blaina tragedy was caused by a backdraught
that was initiated by the transition from compartment
to structural fire as the compartment
boundary (kitchen ceiling) was breached by fire, allowing ignition sources to
transfer into an upstairs compartment that held a significant quantity of of
partial combustion products and unburnt pyrolysis products. However, the backdraught
was immediately followed by a sustained fire throughout the whole house as
the flashover stage was reached.
Signs
and Symptoms of Flashover.
1. A rapid increase in
compartment temperature and in heat from hot gases at ceiling level.
2. Tongues of flame visible
in the smoke layer at ceiling level.
3. Other surfaces giving off
fumes.
There are two basic tactical options that firefighters may utilise for flashover
or backdraught control -
(a) Tactical ventilation and 'air control'.
(b) Three-dimensional water-fog applications.
3.
Reaction Time.
The time that elapses from the moment an initial response of firefighters
leaves the station to the instance extinguishing media is applied to the fire is
termed the reaction time. Its
relevance is a key factor in high-rise firefighting operations and Fog
Attack lists case-histories demonstrating reaction
times ranging from nine to forty minutes in several tall buildings! At
Blaina the reaction time was ten
minutes. With less than half a mile to reach the incident this is an
unacceptable time. In fact it was eight minutes after arrival (post backdraught)
and thirty minutes after the fire was initially discovered that water eventually
reached the flames and then it was applied as a defensive spray to assist the
rescue of two trapped firefighters.
An immediate'direct' attack on the fire, and/or a three-dimensional water-fog application into the gas layers, would
most likely have prevented the transition from compartment fire to structural
fire and reduced the likelihood of a backdraft. The fireground action plan recommends some form of fire attack should
take place within sixty seconds of arrival on scene unless (a) exterior rescues;
or (b) a tactical venting action; are prioritized.
4.
Search & Rescue Time.
Deborah Wallace detailed a number of case studies in her book and
developed the notion that modern plastics play a far bigger part in causing fire
fatalities than is currently realised. A close study of fires in New York,
Dallas and Las Vegas (she referred to several others) suggested that short term exposures to 'modern' fire gases
resulted in long term effects for survivors. The toxicity of such gases, coupled
with the presence of corrosive irritants, asphyxiants, and organic chemicals are
most likely to increase the fatality
rate from fires and damage
the heart, brain, kidney, liver, and respiratory tissue of survivors. These
gases have an immediate effect on the survivability rate of trapped occupants
and Fog Attack demonstrates the direct
correlation between survival rate and performance time - ie; 'time to rescue'. Tests on rats had shown a
46.6% survival rate if rescue was
effected within a 12 to 15.5 minute time scale, but the survival rate dropped to
5.5% when rescue occurred between 15 and 17.5 minutes. I suggested that a
realistic estimate for achieving 'rescue to the exterior' at structure fires
should be within 10 minutes of arrival and whilst the success achieved in any
rescue situation is likely to be in direct proportion to the risk as run by the
rescuers, this proposal is again subjected to risk analysis on scene prior to actioning. In Blaina, it wasn't that
the firefighters took this 'rescue' option as the priority over 'fire attack' -
but simply that they may have achieved both in unison with effective assignments.
5.
Tactical Ventilation and 'Air Control'.
'The
men of the fire brigade were taught to prevent, as much as possible, the access
of air to the burning materials. What the open door of the ash-pit is to the
furnace of a steam boiler the open street door is to the house on fire. In both
cases the door gives vital air to the flames'.
James Braidwood
'Fire Prevention & Fire Extinction'
1866
The authors give their
definition of my term
- 'Tactical Ventilation' in the
updated manual as follows
'Ventilation'
is defined as -
'The
removal of heated air, smoke and other airborne contaminants from a structure,
and their replacement with a supply of fresher air'
'Tactical
Ventilation' is defined as -
'requiring the intervention of the fire service to open up the building,
releasing the products of combustion and allowing fresher air to enter'.
The manual also advises the reader that any ventilation openings should
be made at the highest level first before lower openings are made and great
emphasis is placed on this instruction throughout the text. However, it seems
that so little attention is now paid to Mr Braidwood's most important point from
1866 - how many times do firefighters actually 'ventilate' a high-point prior
to entry? Surely the biggest and most influential ventilation opening we are
going to make in a fire involved structure is at the point of access! - the
doorway. We force our entry and leave a gaping hole behind us to 'feed'
the flames up ahead! Somewhat in contradiction of the definitions on
'ventilation' - do we really want to 'allow
fresh air to enter' ? Ask most firefighters and they will insist on the
access door being left wide open as a means of rapid egress should the
compartment become untenable.
However, Swedish firefighters always partially close the access doorway
behind them to maintain 'air
control' within the fire compartment. The interior crew will constantly
evaluate conditions and take into account any effect the size of the opening has
on the fire's development. This opening can be enlarged or reduced at any stage
of the firefighting operation to influence conditions such as -
1. The height of the smoke layer interface.
2. The amount of heat radiating down from the ceiling.
3. The intensity of the fire.
4. The direction of the fire plume at ceiling level.
5. The temperature within the compartment.
However, closing the access door is likely to increase the production of
partial combustion products and unburnt pyrolysis products and firefighters need
to be aware that further actions are necessary fairly promptly to avoid creating
a backdraught situation.
The manual states, on page 28, that the initiation of offensive
ventilation cannot be
treated as an attack in its own right but I would hope the lead into this paper
would suggest otherwise, where air control
tactics were used in Spain to reduce the fire's intensity.
These effects can be demonstrated in 'container' fire simulations where (for
example) -
Temperature measurements recorded as follows during a 'typical'
simulation.
Close door - temperature drops
850 C - 600 C @ ceiling in 20 seconds.
800 C - 400 C @ 1.6 metres in 20 seconds.
600 C - 300 C @ 1 metre in 20 seconds.
Open door - temperature rises
400 C - 800 C @ 1.6 metres in 20 seconds.
Close door again - temperature drops
800 C - 450 C @ 1.6 metres in 20 seconds.
Radiant Heat Flux repeatedly drops below critical levels (20 kw/sq.m)
each time the door is closed - exceeding this level within 20 seconds each time
the door is opened - directly influencing the likelihood of flashover.
In his book, David Birk describes computer modelling of a 'real' fire in
a hotel room and investigates the varying effects that different access door
openings have on fire growth and development. With the fire initially restricted
to a burning chair he reports time to flashover as being
greatly affected by such openings -
Door open 3 feet - flashover achieved in 2.38 minutes.
Door open 1 foot - flashover achieved in 2.82 minutes.
Door open 6 inches - flashover achieved in 4.28 minutes.
Door open 3 inches - flashover achieved in 6.97 minutes.
Door closed - flashover not achieved.
It was also noted that the hot layer interface, which was measured at 1
metre from the floor with a closed door, rose to about 1.7 metres with the door
opened to 3 feet.
The new manual provides an excellent sequence of photographs from 'an
enclosed room fire', as simulated at the FEU. It should be noted that the flashover
occurs within 3 minutes and 5 seconds from time of ignition, with a fire
spreading from a waste paper basket to involve a sofa, chairs and other items of
furniture. However, the door to the room is left wide open in this experiment.
Whilst it is well established that flashover
may occur, under certain circumstances, within a 'closed' room with the door
closed, what is the likelihood? what time scales are we talking about? and what
factors are relevant? ie; leakage paths; internal pressure or heat levels
capable of causing windows to break; and, how is a fire likely to develop under
such conditions? - a firefighter needs to
know these things, despite the variables.
Stack
Effects.
The movement of smoke in fire involved structures is subject to several
forces -
1. Stack effect.
2. Buoyancy.
3. Expansion.
4. Wind.
5. HVAC Systems.
Although 'stack effect' is due to'buoyancy',
the two are frequently considered seperate forces
regarding smoke movement within buildings. Smoke that has cooled loses
its buoyancy but can still move in buildings if caused to by the stack effect.
Buoyancy typically refers refers to the movement of smoke due to its decreased
density associated with its elevated temperature, thus the smoke moves by
itself. However, 'stack effect' is present in tall structures at all times and
is not a phenomena associated with the fire itself.
The new manual of firemanship fails to grasp this essential feature and
confuses the issue. In Fog Attack I
utilised several pages of text to explain and demonstrate the effects that stack
action might have on smoke movement in high-rise fires. In terms of compartment
fires the effect is highly relevant and may have been responsible for the
loss of a firefighter's life in West Midlands in 1992.
A fire in a residential tower block was contained in one room of a flat
on brigade arrival. As crews entered to tackle the blaze the natural 'stack
action' would have created a negative pressure in the access stairway and
entrance lobby. The strength of this effect, it is theorised by investigators,
may have been so strong as to create a flow of 'pressure' from compartment to
stairshaft, causing the exterior window to break, and driving heat and flames
onto the advancing firefighters who became trapped in conditions likened to a
'flashover'. Another effect, which I had observed at several fires in tall
buildings and given the name 'blowtorch
effect', had also found its way into the pages of the new manual and may
well be associated to the effect of stack action itself. A Home Office
memorandum issued to Chief Fire Officers in 1993 reported on the likely effects
of cross ventilation in high-rise buildings. It informed of
the following -
'some recent fires which have
occurred on the upper floors of high-rise buildings, (where) the sudden failure
of external glazing possibly combined with the influence of high winds, appears
to have resulted in uncontrolled cross ventilation. This has led to an
unexpected and rapid development of the fire, endangering the lives of
firefighters''.
Royal Berkshire firefighters experienced problems when a fire occurred in
a residential tower block in Langley. Smoke logging of upper floors and an
intense 'heat barrier' resulted as exterior glazing failed, resulting in heat
being forced down two levels from
the 12th to the 10th floors. A total of six personnel received burns as the BA
control bridgeheads were forced to retreat on two occasions. A further four
personnel were removed to hospital from the fire floor.
Simon Hoffman reported from a BFSA conference where several renowned
speakers had described similar incidents where smoke, heat and flames had
rapidly moved down several at a time during high-rise blazes. This phenomenon
was described by CFO Graham Meldrum as it occurred at the Merryhill Court fire
in the West Midlands, spreading fire down five
floors from the 13th to the 9th levels! In this instance several firefighters
operating at a 'bridgehead' below the fire became trapped. There were similar
occurrences at the massive 'Churchill Plaza' fire in Basingstoke and at a London
residential tower block where several firefighters were injured.
It is equally important for firefighters to possess an awareness
of stack action and fully appreciate
the likely effects that tactical or unplanned ventilation might have on smoke
movement and fire development within the confines of a high-rise building. A
knowledge of NPP (Neutral Pressure Planes) and the natural flow of air within
tall structures under various environmental conditions is necessary if the fire
officer is to make safe and effective tactical decisions at such incidents.
Four
essential requirements.
Whilst research was being undertaken for the FRDG report!on fire
ventilation I was asked by the authors to comment upon certain aspects
associated with the operational command
of such operations. I highlighted four essential requirements
based on sound tactical decisions -
1. Co-ordination.
2. Communication.
3. Precision.
4. Anticipation.
For successful (and safe) ventilation operations, any attempt to
ventilate a fire involved structure must be carefully co-ordinated with the
interior attack crews (they should 'call the shots'). This requires effective communication
links between the different teams and operational commanders. Any such
openings made within the structure must be applied with great precision
to prevent the fire spreading and the whole process should be monitored with an
element of anticipation as to
what the likely effects might be, siting cover hoselines in advance
where necessary. These essential features are now emphasised in the new
manual and form the basis for all such fireground operations. As in all tactical
options, the outcome may prove beneficial or detrimental to existing conditions,
but tactical ventilation, more than
any other option, must be carefully applied where firefighters are already
advancing within the structure. However, elements of caution should not prevent
fire officers from taking advantage of such tactics - Training provides
experience, provides confidence, provides skills!
Positive
Pressure Ventilation.
The increasing use of Positive Pressure Ventilation (PPV) as an integral
part of tactical ventilation is widely acknowledged although the Home Office are
advising that much training is necessary before PPV is utilised as an 'offensive'
tool. Since I introduced the techniques in the UK a large number of brigades
have purchased equipment and are in the process of evaluating the procedures and
estbalishing their own protocols. Unfortunately, no tangible central guidance
has been published to date. Due to the absence of national guidelines, Tyne
& Wear Fire Brigade has become extremely proactive in this field and
recently embarked upon a series of tests with the assistance of the FEU. These
tests resulted in the production of videos and a comprehensive research report.
Now, with the support!of the Home Office, CACFOA, the FBU and various
manufacturers, CFO Bull has formed a national liason forum and organised
seminars attended by over 40 fire brigades in the UK. There has been unanimous
support!for the concept of PPV and the development of protocols, and two working
groups have been established under the umbrellas of operations
and training, chaired respectively
by Wiltshire and Lancashire Fire Brigades.
There have been several texts in the USA, based upon much fireground
experience of PPV, and I've attempted to produce an overall view of the
experience to date (1992) in Fog Attack. With
a more recent experience base developing in the UK and national protocols being
formulated I would refer the reader on to the Tyne & Wear Liason Group for
advice. However, it is suffice to say that PPV has arrived! In terms of both
'compartmental' and 'structural' firefighting situations the benefits to be
derived from such techniques have to be seen (and felt) to be believed.
Tactical
Ventilation - the future.
In 1993 the FEU distributed questionnaires to 66 UK fire brigades and 47
responses were received. Only fifteen per cent of fire brigades stated that they
were actually promoting the use of tactical
fire ventilation . At that time a small number of brigades (six per cent)
were evaluating the strategy and another six per cent were flexible in
encouraging their officers to decide for themselves on scene. The fire
authorities that did promote venting tactics admitted they had no structured
training or literature available and relied upon the briefest of descriptions in
the manuals of firemanship, coupled with past experience, to provide a knowledge
base for practicing the techniques involved. Compartmental ventilation tactics
differ greatly from structural ventilation tactics in as much as less training,
equipment and manpower is needed to operate safely and effectively at fires that
have not spread beyond the original compartment of origin, providing of course
the compartment is of reasonable dimensions! However, there is a natural
reluctance amongst many at making positive moves; moves that will ensure the
strategic principles of tactical ventilation evolve as part of our fire control
philosophy, and because of this, it may take years of research and testing
before the overall benefits are universally accepted with confidence.
6.
Water Applications.
Direct
Attack.
Water has been known as an extinguishing agent as long as fire has been
known to man. However, its full potential as an aid to firefighting has yet to
be realised, for whilst the heat absorption capacity of water is greater than
practically any other substance available, the ideal application has never been
achieved on the fireground. In relation to Heat Release rate (HRR), or fire
'intesnsity', a flow of one litre
per second possesses a theoretical cooling capability of 2.6 MegaWatts (MW),
although in practical terms a capability of 0.84
MW per litre per second is perhaps more
realistic. Putting these figures into perspective, it is known that a
single foam filled chair may provide a HRR of 4-500 KW, well within the
capability of a single hosereel attack. However, modern office 'work-stations',
comprising of furniture, computer terminal and stationery etc, are known to
achieve HRR's of 1.7 MW (two-partition) or 6.7 MW (three-partition) on their
own. At the Interstate Bank Fire in Los Angeles it was estimated that involved
'work-stations' achieved a 10 MW Heat Release Rate within 2-3 minutes of origin!
Large amounts of water are required to handle such heat outputs. To the
firefighter, this means that the nozzle in use has a maximum 'practical' cooling
capability and reliable estimates may be given as follows;
50 LPM - 0.69 MW
100 LPM - 1.39 MW
150 LPM - 2.10 MW
200 LPM - 2.79 MW
300 LPM - 4.20 MW
550 LPM - 7.69 MW
800 LPM - 11.19 MW
1000 LPM - 13.99 MW
With fire stream reaches in excess of 40 metres, combined with great
striking power and penetrating properties, the 'direct attack' has
enabled firefighters to advance into large structures to complete extinguishment
from a 'safe' distance. However, the degree of efficiency for such an approach
has been estimated at about one third of the theoretical capability. In other words, up to
two thirds of water applied at the base of a fire will run-off and have no actual
extinguishing effect. Even so, the
'traditionalists' approach to 'straight-stream' fire attack has proved the most
dependable and remains the popular approach despite the associated water damage.
Indirect
Attack.
The description 'indirect
attack' lends itself to techniques developed in the USA during the 1950s
where water is applied 'indirectly', away from the fuel source, in the form of a
spray. The application is directed onto hot surfaces, such as walls and
ceilings, in order to produce large amounts of steam (a 10 to 35% mix of water
vapour with gases) that smothers the fire
in the room. Whilst an amount of success was achieved in terms of 'fire control
times' and a reduction in water damage over 'direct' attack methods, the process
of 'indirect attack' presented new hazards to the firefighter when applying
water within the confines of super-heated fire compartments. The rapid
conversion to water vapour was often seen to create excessively high compartment
pressures that caused steam, and sometimes fire, to 'envelope' back onto the
advancing firefighters. It also became apparent that a pressure wave moved ahead
of the fog stream, pushing heat and flames into remote areas of the structure
and sometimes causing trapped occupants to leap from upper windows. These
undesirable effects ensured the techniques were to fail in their tactical
advantage and the 'direct' approach prevailed.
Note:
For the reader's
information, an updated calculation for 'Indirect' attack, as produced by the
Fire Research Station in England, is included as Appendix 1.
Three-dimensional
water-fog attack.
A fairly recent development has been the three-dimensional approach by Swedish firefighters who apply a fine
mist of water droplets into the super-heated fire gas layers that exist near the
ceiling. The technique, also known as offensive
firefighting, is not intended
to complete the extinction process in a compartment fire but serves to mitigate
or prevent the hazards associated with flashover and backdraught. The 'misting'
can also be utilised to extinguish burning gas layers following flashover. To
complete the extinguishing process
the nozzle operator should eventually resort to a 'direct' straight stream
attack or a second hoseline should follow up extinguishment of the burning
items.
The three-dimensional water-fog application, which is applied in terms of
'cubic metre' coverage, as opposed to the 'square metre' coverage of an
'indirect' application, has been most effective in providing firefighters with a
'safer' environment in which to work. The operator avoids contact with walls and
ceilings and directs the fine 'mist' into the gases, causing them to cool and
contract. This results in minimal steam expansion and pressure build-up,
therefore preventing the hazards so often associated with the 'indirect'
approach. However, the application requires great precision, relying on several
factors such as (a) size of water droplets in stream; (b) correct nozzle and
cone discharge angles; (c) effective application by trained operators, avoiding
over-drenching of the gas layers and surfaces; and, (d) a nozzle capable of
discharging an effective pattern with sufficient flow.
Water delivery rate.
There have been two or three attempts at producing a formula that predicts fireground water delivery rate. The uses of such an application are obvious in terms of both fire protection and firefighting requirements but the reliability factor of associated calculations has often come under major scrutiny. However, in Fog Attack I explained how my own research had produced a formula that demonstrated the highest reliability factor of all formulas in current use, with a 41% success rate. The 59% of occasions where the formula was 'out' we