PUTTING THE WET STUFF ON THE
RED STUFF
On the effectiveness of Water
Spray Systems (sprinklers) in controlling fires in High-Rise Buildings and some
recommendations in the wake of the World Trade Center disaster.
By Arthur Scheuerman, Retired Battalion Chief
FDNY
I read the extensive, May, 2002, FEMA, ASCE
report on the World Trade Center Fire and have a few disagreements, one of
which concerns Water Spray Fire Extinguishing Systems. The statement, that “…sprinklers
are not normally capable of controlling fires that are of a large size before
the sprinklers operate” (p1-16) seems a widespread belief held by engineers. Having
spent most of my life fighting fires I know there are situations where fires
cannot be extinguished by interior hand held hose lines but that these same
fires can be controlled by ‘sprinklers’. At one apartment fire that I was in
charge of, a team of experienced aggressive firefighters could not advance down
a hallway to extinguish a large apartment fire because of a strong wind blowing
into the broken out apartment windows, accelerating the fire, and projecting a
large flame front down the hallway. The only problem was that we couldn’t get
any water into the main body of fire, since, due to the extreme heat and flame
blasting down the hall, the men couldn’t advance to a position from which they
could hit the main body of fire, The firefighters had to be ordered out when
their turnout coats began to steam and smoke from the heat threatening to cause
serious burns after their repeated attempts to ‘make it’ with hose lines. I know from experience that two or three water
spray heads from a water spray system directly over this fire would have made
short work of it.
As it happened people were trapped over
this fire and the fire was burning through the floor threatening to extend to
the floor above. If the apartment on the floor above the fire ignited and these
windows broke out due to the heat and pressure of the fire, allowing the wind
to enter on this floor, we would have had two floors of fire that couldn’t be
extinguished from the inside, and the fire would have taken the building by
advancing up from floor to floor with certain loss of life. Fortunately the
apartment was on a lower floor which could be reached by an outside master
stream which was used to knock down the fire and control this situation. If
this fire was in a brick and wood joist High Rise building, on an upper floor,
out of reach of outside streams, it could have been a tragedy. The point is that
water spray systems (sprinklers) can often quickly control fires inaccessible
to hose streams. This capability is especially critical in High Rise buildings.
Getting fast water on the fire is perhaps the most important life saving
measure at almost every serious fire. Water spray systems are designed to do exactly
what the Engine Companies are trying to do, only they do it faster and cover
more area with the exact water spray pattern needed for rapid fire control.
I am using the term water spray system rather than
‘sprinkler’ because I
believe one of the main reasons that ‘sprinklers’ are devalued and not
installed is that people have a heard time believing that ‘sprinkling’ water on
a fire could be more effective than a Fire Dept. hose team with a high volume,
water stream. When I was a firefighter it was difficult to admit that water ‘sprinkling’
from the ceiling could be more effective than my fully equipped Engine Company
manning a charged two and one half inch hose line. I believe the word
‘sprinkler’ should be changed to ‘water spray system’ to remove the weak image
created by the word sprinkle, so builders will be less reluctant to install
them.
In point of fact water spray systems were originally
invented to extinguish cellar fires inaccessible to Fire Dept. hose streams.
Cellars and sub cellars in the old NYC commercial buildings were very difficult
and dangerous fires to fight since a hose line had to be advanced down the
cellar stair when all the smoke and heat and flame, being produced by the fire,
were coming up the stairway. Once down in the cellar, if the fire could not be
controlled, escape for the hose crew required advancing back up through this
heat to safety. To solve this problem lengths of iron pipes, with holes drilled
in them, at various angles, were installed along the ceilings of cellars and
sub-cellars in these buildings. These pipes were called dry pipes since they
contained no water until hose fittings were attached on the street level and
the Fire Dept. pumped water into these systems. It proved a more effective fire
suppression method to apply water directly over the fire through these
pre-installed, perforated pipes than by exposing a hose crew to the hazard of descending
a cellar stair the opening of which was belching large quantities of super
heated suffocating smoke. At times it was the only practical way to safely
control the below grade fire, after it became fully developed. Present water
spray systems evolved from these nascent ‘sprinkler’ systems.
I believe, contrary to some builders, that a built in
water spray system is probably the only practical way to extinguish some ‘large
floor area’ interior fires which are out of reach of outside master streams. I
base this judgment on the rapid fire control which I’ve seen accomplished at a
fully involved lumber yard fire by a single jumbo fog nozzle placed on an
aerial ladder and extended over the fire in order to cover the entire involved
area at once with water spray. This action produced a large area spray, very
similar to the coverage that a water spray ‘sprinkler’ system is designed to accomplish
in a building. It is my opinion that, the difficulty extinguishing ‘large area’
interior fires exists because all areas of the fire cannot be cooled at once with
hose streams (which only have a reach of about 50 ft. and cannot spray around
corners) and as these interior hose streams are repositioned, the fire
reignites in the area just extinguished, by convected
and radiated heat from the main body of fire. A hose crew can only take so much
punishment from such an uncontrolled fire before being knocked out by the heat
and smoke.
In the New York Times article “Defending Skyscrapers
Against Terror” (Science times, Sept. 18, 2001) the statement by an engineer that
“sprinklers would have been useless against a fuel fire” and that “droplets of
water sink into the fuel, turn to steam and explode” seems a typical
misunderstanding, is misleading and further discourages installation of these
water spray systems. Water spray from hose nozzles are used all the time by
Fire Departments even at gasoline or propane fires to control the heat output
and protect lives and property . It is
by turning to steam that water exerts its maximum cooling capacity. The
expansion of water into steam is the main cooling phenomenon used in
extinguishing practically every type of fire, every day, by firefighters. The
latent heat of vaporization for water is prodigious. Every pound of water
turned into steam removes 907.3 BTU’s of heat from the fire. In every interior
attack, as firefighters open the nozzle and direct the water stream into the
‘main body of fire’ it creates an expanding cloud of steam mixed with smoke.
This conversion/ expansion process cools the super-heated fire gasses and
combustibles to a temperature below the ignition point thereby effecting fire
control and extinguishment. This expanding cloud of smoke and condensing steam
may be uncomfortable or even dangerous for the firefighters for a short time.
But this additional heat felt upon opening the nozzle is an indication that the
‘main body of fire’ has been hit and is probably ‘knocked down’ and the nozzle
can be shut down momentarily to reduce this discomfort while the condensing
steam and smoke ‘lifts’ and is ventilated, dissipating its heat to the outside.
An experienced hose team realizes that opening a nozzle into a well developed
fire is going to produce steam and is careful in the beginning to first “give
it a dash” to gauge the amount of steam produced so as not to scald the hose
team.
At the World Trade Center fire, in my estimation, a
water spray, immediately directed into the fire after the planes crashed into
the buildings, would have both helped cool the area and expelled (by the water
expanding 1600 times upon conversion into steam) more of the burning fuel mist and
vapor to the outside of the buildings through the blown out windows. If a
sprinkler system had remained intact, after the plane impact, it would have
retarded the fire growth and smoke production to help protect the people; and by
reducing the heat output cooled the interior areas and the core and perimeter
columns, the floor truss assemblies and the critical column to truss
connections which appear to have been the first element to fail, letting down
the floors which started the progressive collapse.
The truth is water spray systems ‘sprinklers’ are
probably the most effective fire control method generally available for the
great majority of fires. Such fire suppression systems have saved unknown
numbers of lives, including firefighter’s lives by the immediate control of the
heat and smoke buildup of a fire before they can escalate to deadly
proportions. Water, a most effective cooling medium, is available immediately
in exactly the right place, in exactly the right volume and spray pattern for
fast control of the dangerous heat and smoke buildup from practically all types
of fires.
The statement
(N.Y.Times, Sept. 18, 01) that they only “put out a few hundred gallons a
minute for half an hour” is also misleading. The initial ‘one half hour’ house tank water
supply is there to quickly operate the spray heads until the Fire Dept. arrives
and supplies water continuously by pumping into the street level hose
connections.
Since the concept that ‘sprinklers’ can control a
fully developed large area fire now seems controversial; and in order to settle
the question, I recommend that water spray system tests be incorporated into
the full scale structural fire endurance tests to be conducted by FEMA and NIST.
These tests could be conducted in the same test structures built to determine
structural steel endurance times and failure mechanisms, by installing water
pipe systems and running the water spray suppression tests before the
structural failure tests. Some idea of the degree of protection afforded the
steel by water spray systems would also be gained.
The idea that, in N.Y.City, water spray systems can
only supply enough spray heads to control a small area fire is erroneous. Water
spray systems are required by the New York City Building Code to have large
enough pipes to hydraulically supply all the heads on a floor or within any
area between fire walls with the proper volume and pressure. According to this
code “… the possibility that all or most of the sprinklers might be opened by a
single fire should be considered in determining the size of the risers.”
(Chapter 3, Sec. 3-4 Pipe Schedules, RS 17-6) If, in the design stage of a building, it is
required but not possible to hydraulically engineer a system to properly supply
all the heads within a proposed area, due to friction loss or water supply
considerations, you cannot just eliminate the system; you must reduce the area
to a size that can be effectively covered by the water spray system or install fire
walls to effectively accomplish the same thing. Of course the size of areas
between fire walls should be limited anyway since sprinklers are sometimes down
for repairs and the area of fire that can be controlled by interior hose
streams is limited.
It seems to be an ongoing problem in tall buildings-
eliminating all the openings in fire walls and fire barrier floors. In large buildings some areas or others are
always under renovation and new poke through openings for pipe and wiring runs
are made by contractors and trades people who may not understand the importance
of integrity of fire separation barriers.
Fire and smoke can extend through a small opening in a rated floor or
wall and in short order, spread a fire to another area or to the floor above. According to a report by the NY Board of Fire
Underwriters after an investigation of a previous fire at the WTC (report
titled One World Trade Center Fire, February 1975).
* “Unfortunately, no provision seems to be made for
protection of openings in floors or walls. Consequently, some of the holes are
not filled or others are filled with materials that disappear in the first
seconds of a fire. It is ridiculous to spend time and money to prove that a
floor or wall can withstand a two-hour fire and than allow holes to be cut in
it that destroys the fire resistance”.
Unprotected ‘access stairs’ between
floors seem to be another common hazard, which could spread fire to another
floor, in large area high-rise buildings.
Recommendations
for Water Spray Systems in Tall Buildings
‘Combination systems’ which combine standpipe and water
spray systems should not be allowed in high rise buildings since breakage in
one system affects operability of the other. Separate systems increase
dependability.
I believe the Codes
for water spray systems should be strengthened in High Rise buildings to
provide increased water flow and pressure capacities and protection for pipes
by increasing the size, strength of pipes and hangars and, enclosing risers in hardened
shafts. Providing redundancy in supply by feeding floor pipe grids from several
directions by separate risers protected by check valves. If one riser breaks and
is depressurized the check valves would close due to the pressure from the
other riser(s) and the area remains protected. Branch line shut off valves
could be provided on each floor, in hardened stairways for Fire Dept. access,
to shut down broken sections of supply mains, in order to preserve water
pressure in remaining sections. Perhaps automatic sealing devices for broken
pipes could be developed.
Redundancy in water supply tanks and water pumps could
be improved.
It may be
possible run two risers in each hardened stairway or separate risers in
separate enclosures in order to supply alternate floors with different risers.
In case of floor collapse the spray heads on the floor above the collapsed
floor would remain pressurized to control the fire. Separate water supply could
be provided for each riser. This configuration would also better protect ‘openings’
in the floor which may permit fire to extend to the floor above. If one floor
were fully involved by a flash fire and the heat opened all the spray heads,
taxing flow capacity and pressure requirements on that floor and the fire
extended to the floor above through openings in the rated floor, the spray
system on the floor above would still have adequate water to control the
extending fire. Alternate floor, riser connections in a hydraulically
engineered water spray system will assure sufficient water pressure in the
system to control such extending fires.
Additional
Recommendations
We are also in need of a convenient material to
re-plug, poke-through holes made in fire walls and fire barrier floors; perhaps
an approved spray can that injects an expanding fire proof material into such
openings after the wires or pipes are run. Such spray cans could also be developed
for re-protecting steel exposed by accidentally damaging fireproofing, during
renovations.
* Reprinted from “Firefighting Strategy and Leadership”
Walsh and Marks, Second edition, McGraw Hill, p46
Arthur
Scheuerman,
Retired
Battalion Chief, FDNY
E-mail – acaj1@aol.com.