BY FRANCIS L. BRANNIGAN SFPE (FELLOW)
In many areas of the country, the increased sizes of homes can pose challenges of “monstrous” proportions for firefighters responding to fires in these structures. Some of these challenges are discussed below, as are some ideas for educating the public about these lurking hazards and some steps they can take to prevent fires and increase their chances for survival should one occur.
How would you like to deal with a fire in an 8,000- to 10,000-square-foot private home? People with lots of money in the Washington, D.C., suburbs and those in or near New York City, Chicago, Denver, Salt Lake City, Minneapolis, Philadelphia, and other locations are buying houses of this size to show that they have made it. A Texas residence, two stories high and covering 43,000 square feet, burned at a loss of $40 million.1
The families who live in these houses often consist of two adults and two children, each with their own bedroom and bathroom. The houses generally include several bedrooms, media rooms, a private bath for each occupant, home offices, a sauna, and fitness and other special-purpose rooms. According to Gopal Ahluwalia of the National Association of Home Builders, “People use the kitchen, the family room, and the bedrooms.” But, victims may be anyplace in the huge and confusing house.
(1) This imposing home gives the appearance of a “brick building.” (Photos by author.) In fact, it is a wood-frame building with a brick veneer facing
(2) Its stability depends totally on the lightweight wood construction. I have yet to hear “a brick veneer building” identified in a preliminary size-up report. Know your buildings, and describe them properly.
SOME CONSTRUCTION SHORTCOMINGS
Most of the houses present a brick appearance; but in many if not most cases, they are brick veneer, which presents a collapse hazard. Stability is totally dependent on the wooden wall. A Dallas, Texas, firefighter died in the collapse of a brick veneer wall. The wall collapsed in what Fire Department of New York Deputy Chief Vincent Dunn defines as a 90° collapse—the wall fell flat out its full height.
Since the ceilings are higher (as high as 11 feet) and the rooms are larger, larger furniture is required, thus increasing the fire load. The larger sofas (18 inches longer and 10 inches deeper than standard units) increase the quantity of polyurethane. The floors, most likely supported by trusses or wooden I-beams, create voids through which fire can spread like a cancer. Wooden I-beams should not be considered fire stops. Without loss of structural strength, they can be and are cut for wiring or air ducts. Knockouts are provided. The interior has soffits or other departures from simple square box construction. These voids are interconnected. The buildings may be platform frame structurally, but they are balloon frame from our point of view.
Some or all of the fire protection deficiencies of wood stud and gypsum board construction are cited in the sidebar “Fire-Resistance Ratings and the ASTM E119 Fire Resistance Tests.” (Also see BCFS3, Chapter 5, regarding garden apartment and other “protected combustible” structures.)
The term “protected combustible” applied to these structures should not be taken to indicate a structure is safe to operate in once the fire involves the gravity resistance system (GRS). There may be large areas of attractive wood paneling. If it is furred out from gypsum board, fire can burn on the rear side unhindered by fire streams. If the paneling is applied directly to the studs, it admits fire almost immediately to the structural system of the house. The floors may be rated for fire resistance (see sidebar “Fire-Resistance Ratings and the ASTM E119 Fire Endurance Test”), 2,3 but such ratings have serious deficiencies (see BCFS3, 537-541). Floor trusses may be cantilevered out to form balconies or false mansards.
The interior construction resembles balloon-frame construction with respect to fire spread through voids. The master suite may be at one end of the house and the other bedrooms at the other end. There is nothing resembling a standard layout. The parents may have one exit and the children another.
It is very stylish to have a brick, slate, or even marble entryway. The floor system is cut down; ledger boards are nailed to the joists, and short pieces of wood are set on the ledger boards to provide support for the concrete bed for the stone so the finished masonry floor will be level with the room floor. It is very vulnerable to fire below. The fancy foyer may drop the first-in crew into the fire.
Preplanning note: To determine if this hazard will be present in the finished building when the building is under construction and there is no one to ask, see if the floor extends to the door or if there is a pit for a masonry floor.
These houses are often built in areas where fire department initial response times may be much longer and staffing leaner than for departments in the cities where the occupants formerly lived. The additional resources needed for a major fire will have longer runs.
There may not be a municipal water supply. Tankers, swimming pools, or relays may be the only resources. In any case, preplan the water supply. Some years ago in a rural area of an urban county, a preplan for a rural feed mill called for a relay operation from a nearby pond. The first-in officer, seeing just light smoke, canceled the relay. The mill burned to the ground. It is not likely that you will come up with a better plan on the spur of the moment than one that you developed while not under pressure. In my experience, “light smoke showing” is often the first report of a multiple alarm.
(3) Structurally, this is a platform frame building; firewise, it is the equivalent of a balloon-frame building. The floor voids are interconnected by
(3a) utility piping such as this plumbing vent.
(4) Wooden I-beams are no better than trusses as fire stops because they legally can have holes for wiring and large holes for ducts, metal, or plastic.
(5) In some cases, an unprotected steel beam or a flitch plate girder (see photo 9) is used to provide a wide, clear span. The failure of a steel beam cost the life of a Georgia firefighter.
(6) The peaked roof is supported on lightweight wood trusses. Personnel operating from a tower ladder should perform ventilation. No code requires that the roof be a safe operating platform for firefighters
(7) Imitation wood shingles, made of concrete, are sometimes used. They are a heavy dead load on the roof.
FIRE DETECTION AND SPRINKLER SYSTEMS NEEDED
Occupant safety demands sprinkler protection. Residential (partial) sprinkler systems are intended to prevent flashover to permit occupants to escape. They do not cover hidden voids and possibly other spaces. They do not guarantee property protection.
I looked at some high-priced townhouses with residential sprinklers under construction and noted no sprinklers in the double garage. I was told that the overhead trusses were not strong enough to support the sprinklers (I doubt it), so doubled gypsum board was installed on the ceiling. A garage fire could kill the occupants.
Partially sprinklered buildings can be destroyed by fire, untouched by sprinklers, moving through the voids. An outside exposure fire penetrated the exterior of a multistory apartment house in Solomons, Maryland, and spread through the voids unaffected by operating sprinklers.4
Most builders are opposed to sprinklers: “Another picky inspector to slow down the job!” An exception is Thomas Bozzutto, a builder and housing manager in the Washington area. He and his wife went to bed with a lighted candle on the deck. The house was destroyed. Their new house is sprinklered.
Smoke detectors should be placed in every individual space, including attics. The detectors should be interconnected so that if one sounds, they all do. There should also be a battery backup in all units and a connection to the fire department through a private alarm service.
Consider the following scenario: You arrive at the scene of a residential fire at 2 a.m. to find mother, father, and sister on the driveway. They are screaming that their teenage son and brother must be in the building. “He was still out when we went to bed, but he never stays out this late. Where would he be?” The mother thinks he’s in his bedroom. His father thinks he fell asleep at the keyboard in the computer room. His sister interjects, “Daddy, don’t you remember that he often goes to the whirlpool and then falls asleep in the sauna?”
His bedroom is upstairs, the sauna is in the basement, and the computer room is on the main floor. Try calling him on his cell phone, which may be glued to his ear. It just might work. The mother suddenly remembers the maid, Maria, sleeping in an attic bedroom. This raises the question of how to organize the search. Your thoughts are invited.
Interior command reports that the thermal imaging camera shows heavy fire in the void of the truss floor in the living room, which is right at the entrance way. What does the IC do?
“I’m real sorry folks, but I am about to order my personnel out of the building because of the collapse potential. If I ordered or permitted personnel to attempt to search this building, and they were injured or killed in a collapse, I could be indicted for criminal negligence and be subjected to a ruinous civil lawsuit.”
As I was about to send this article to the editor, I spoke with Richard Freas, one of my first students who is now a deputy chief in the Howard County (MD) Fire Department. He told me of a recent fire in a monster house. He evacuated the firefighters; shortly thereafter, air-conditioning units hidden in the attic came crashing down. Such units may be resting on wooden I-beams or hanging from trusses. Some years ago, a unit fell on Louisville firefighters as they advanced the first attack line up a garden apartment stairway.
The compressor may be in the yard, but several fan units are almost certainly overhead because of zoned supply. Years of experience with ordinary dwellings do not prepare you for a fire in a monster house. Like all buildings, they are your enemy. You must know them and beware. Cope with these buildings with realistic preplanning to avert a tragic experience.
(8) If the building is sprinklered to the 13R standard, fire can and has spread through unsprinklered voids. All sleeping rooms and adjacent corridors should have smoke detectors. A smoldering fire can generate toxic gas.
A NOVEL SUGGESTION
I think we should level with our potential patrons and avoid the “Why didn’t you tell me before the fire?” scenario. A good example of this occurred at Navy Norfolk. A row of sought-after senior officer residences dating back to the James-town Exposition of 1904 was a potential deathtrap. We made a thorough inspection whenever there was a change of tenant. Fire Prevention Captain Benjamin Barry, an aggressive straight-talking inspector who usually worked construction with good effect, was conducting such an inspection. With him was Captain Rimmer of Ladder One. Our officers were taught not to be bashful in pointing out hazards and to call for help if they were unsure rather than bluff. The new tenant, a Navy captain, came upon them and made the usual snide remark about two civilians doing one job. Barry was up to the challenge: “I’m from Fire Prevention. We do our best to see that this firetrap does not catch fire. This is the captain of the ladder company (officer and five firefighters). He is looking to see, considering all these trees, how he would get you and your family out if there were a fire.”
The captain asked, “Is it that bad?” Barry gave him a rundown of the building’s deficiencies. The captain went to the housing officer and changed his residence to one of the smaller new brick houses on the next block.
In 1970, I wrote “Building Weaknesses: Do You Know Them?” for the National Fire Protection Association’s Fire Command magazine. In the article, I deplored the fact that fire departments assumed responsibility for losses they could not control. I outlined the hazards of ordinary commercial buildings and then closed with the following:
“The obvious answer is that the building should be sprinklered. As a matter of fact, considering the hazard of fighting basement fires, some codes require sprinklers in mercantile basements. The owners and occupants of such premises fight sprinkler requirements vigorously. Often the building is of such low value that sprinklers cannot be paid for out of ‘insurance savings’; it costs as much to sprinkler a ‘dump’ as a first-class building. If a building is ‘not worth sprinkler protection,’ is it worth a life?”
I asked the following: “Why not abandon the outmoded concept that every ‘dump building’ is worth saving? Why not identify the buildings that present unwarranted life hazards and deal constructively with the problem created by their existence? Why not be the first fire department to write a letter such as the following?”
Xyz Fire Department
To the owner and occupant of the premises at 123 Blank Street:
- Using a fire extinguisher is a judgment call. Call for help before you use the extinguisher or the garden hose (this same caution applies when starting CPR—call for help first).
- Stop, drop, and roll if your clothes catch fire.
- By definition, your house is a combustible building. To some extent, gypsum board is used to delay the transmission of fire to the inner structure, but there are many points of potential failure. Requirements for smoke detectors are intended to provide an early alarm so you can evacuate. Heights of windowsills from the floor are regulated to permit windows to be used as exits. The use of plastics in furniture has greatly increased the fire and toxic gas load of the contents.
- Install automatic sprinkler protection. Residential sprinkler systems are life-saving devices that will not necessarily protect the property. They are intended to prevent flashover of a contents fire before the occupants escape. They are not installed in the many hidden voids in the structure.
- Have regular home fire drills, particularly when guests are present. Suppress any tendency of “laid back” offspring to show a lack of respect for the drill. In a fire, there are two types of people: the quick and the dead. College students who hide in closets to avoid evacuation during drills will die in real fires. A fire in your home will be the most terrifying experience of your and your children’s lives. Hold a drill just before morning wake-up time to get people to react properly when awakened from sleep. Have an agreed point where all will meet. Many have died going back into burning buildings to “save” someone already out or a pet. You can’t do it. Forget the movie heroics.
- Keep a cell phone at hand or in a car. Get out. Stay Out, and call 9-1-1 from outside. A building on fire is an incredibly dangerous environment. If you have anything worth risking your life for, keep it in a bank vault.
- If you smell smoke or gas, clear the building and call 9-1-1. Do not waste time looking for the source of the smoke. Fire can be burning in a hidden void and be ready to burst out in a massive attack. It is the fire department’s function to determine if a hostile fire is causing the smoke. It is not a “false alarm” if no hostile smoke source is found.
- When the fire department arrives, it is the commander’s urgent duty to determine the location of the fire if it is not known. If the fire is in contents and has not extended to the building’s structure, the firefighters will extinguish it. This may involve opening the roof to vent the heat and smoke to speed extinguishment.
- A search for a missing victim in a house the size of yours with a layout that is totally unfamiliar to the firefighters and in solid smoke-created darkness would have a slight chance of being successful. In fact, the risk/benefit analysis the incident commander (IC) must make might well indicate that the risk of losing firefighters’ lives is greater than the chance of successfully finding the missing person alive.
- Do not smoke in bed or when sleepy. Numerous fires have started because individuals, possibly under the influence of liquor or drugs, fell asleep in a bed, chair, or couch while smoking.
- Never leave a burning candle unattended. Permit no candles in bedrooms. Do not go to bed with candles burning, even outside on the deck. Groups of candles can generate very high heat.
- Use electric lanterns and flashlights if power fails. Keep one at each person’s bedside. Try crawling out of your bedroom to an exit while blindfolded. The usual “landmarks” are not visible from the floor level. A survivor of a multi-fatality fire related: “You think you know your own house, but you don’t.”
- Keep grills away from the house. Do not use the garage for shelter while grilling if it is raining. Be sure the gas connections are tight. Check for leaks with soap bubbles, not a match. Place ashes in an old-fashioned metal garbage can. Put on the lid, and move the can away from the house. Never bring the grill into the house. Never “perk up” a failing fire with a spray from the can of lighter fluid. The can may explode; horrible burns can result.
- Use a screen near fireplaces. Sparks have ignited carpets and caused fires. Do not burn trash in the fireplace; it can flare up and ignite the contents of the room. Place ashes in a covered metal can, and keep it away from the house. Paper bags and cardboard boxes have been ignited from “cold ashes.”1
- The pilot flame on a gas water heater has ignited gasoline vapors, causing terrible injuries and ultimately death. Fill the lawn mower outside from a metal gas can stored outside.
- Never leave a stove unattended when using cooking oil. Shut off the burner before you go to the door for any reason. You may be delayed in getting back.
- If a lighting strike seems close, check the attic for a possible fire.
A recent survey of your building by this department shows it is of ordinary brick and wood-joisted construction without adequate separation into fire areas. In the event of a serious fire, the property would be subject to total loss. During fires in buildings of this type, this department and other fire departments have suffered unnecessary injuries and deaths. To prevent your building from being a deathtrap for firefighters in a fire, we recommend that you have installed a complete wet pipe automatic sprinkler system.
In addition, the following structural improvements should be made: (list them) _________.
When these improvements are completed, and if they are maintained, it is most unlikely that there will be a serious fire in your building. We recognize that you may find these fire defense measures economically difficult, if not impossible. On the other hand, we have a duty to protect all the taxpayers from the costs incurred when firefighters are injured or killed. Until you are in compliance with our recommendations, our fire department will not permit its members to enter your building in a serious fire except to rescue human beings. Firefighting efforts will be confined to protecting nearby properties and extinguishing fire in your property from safe points of vantage.
In view of this determination on our part that a serious fire in your building represents an unacceptable risk of unwarranted expense to the city and risk to firefighters, it would certainly seem prudent that you try to ensure that any fire that occurs will be minor.
The following recommendations are pertinent:
1. Be sure that all your employees understand that the fire department is to be called immediately in the event of fire or the smell of smoke. This is to be done before any search for or attempt to fight the fire is made. We have only a few minutes to save your building. Don’t waste them. You can call us at this number _____.
2. Other pertinent recommendations (add as necessary).
(signed) I.M. WITHIT, FIRE CHIEF
The suggestion turned out to be far ahead of its time. I do not know of any such letter ever being sent. The general reply when I discussed it went like this, “We are sworn to protect life and property; injuries and deaths are part of the job.”
In the wake of 9/11, many fire departments have reexamined their policies, placing firefighter safety at the head of the list of priorities.
EDUCATE AND WARN THE OWNERS
I think the fire service should level with the owners of monster houses. We must tell them that they live in a hazardous situation and must be ever vigilant and prepared to react immediately to rescue themselves if a fire occurs. Prepare and distribute a flyer to community residents (see the sidebar ” ‘Tell It Like It Is’ Flyer for Residents”).
The following messages can be boxed in and used as fillers (food for thought) in your fire prevention materials.
You might include as a tagline at the end of your flyers a message such as the following: “Each year, the President proclaims the first full week in October ‘Fire Prevention Week.’ During this week, we increase our efforts to educate the public in fire safety, but to us, Every Week Is Fire Prevention Week!”
“If you have any questions please call [number of fire department contact person].”
1. “Big, Bigger, Best,” The New York Times, June 20, 2002, D1.
2. See BCFS3, 544-546.
3. At one time in his career, FDNY Chief of Operations John Norman, author of Fire Officer’s Handbook of Tactics, Second Edition, published by Fire Engineering, was a chief officer in his local volunteer fire department. The procedure was that all chiefs were alerted to listen to a fire being reported. Norman heard the report of a bedroom fire. He responded with a six-minute run to a house that had fire coming out of every window. The building was lined in wood.
Thanks to the fire officers who contributed information for this article.
FRANCIS L. BRANNIGAN, SFPE (Fellow), the recipient of Fire Engineering’s first Lifetime Achievement Award, has devoted more than half of his 62-year career to the safety of firefighters in building fires. He is well known as the author of Building Construction for the Fire Service, Third Edition (National Fire Protection Association, 1992) and for his lectures and videotapes. Brannigan is an editorial advisory board member of Fire Engineering.
“TELL IT LIKE IT IS” FLYER FOR RESIDENTS
Because of its size, complexity, and combustible construction, your home would be a very severe life safety problem if a fire occurred. Admittedly, fire is an unlikely occurrence, but many people die every year in fires in homes where the possibility of a fire was the furthest thing from their minds.
Tests at the National Institute for Standards and Technology have shown that a fire started by a match igniting newspaper on a couch will go to flashover (every combustible in the room is burning) in four minutes.
Do not be deceived by the fake gas fires on metal scenery or computer-generated fires shown in movies and on TV. If a real fire were shown, you would see nothing. Fires generate dense quantities of black smoke and toxic gases that will disrupt judgment and cause collapse. Be sure your children understand that they must get out now and stay out. Children are often found dead in favorite hiding places.
Literally, your home is a storehouse for contents and combustible construction materials, which are actually solidified toxic and flammable gases that can be released by a match. Consider the following suggestions:
Since your house is already built, the cost of sprinklers would be very high because of the perceived necessity of having to hide all the piping within the walls. If the piping were left exposed, the cost will be far less. Paint the pipes (but never the sprinklers) the same color as the ceiling. If you can endure the Psychology 101 “experts” calling you “paranoid,” paint the pipes red, and assure your guests that it is a sound sleeping aid. Install smoke detectors in all spaces including bedroom walk-in closets and hidden spaces such as attics. You can have a raging fire in the attic and other voids and not know about it until a neighbor calls and asks, “Do you know your roof is on fire?”
All detectors should be wired so that all will sound if any one detector operates. The detectors should have battery backup. A fire might disable the electrical system.
A fire in the hidden structure of the building involves the building’s combustible gravity resistance system and is an infinitely greater and more dangerous problem than a fire in contents only.
When it is determined that an imminent collapse or flashover (all contents and surfaces ignite simultaneously) potential exists, the IC must order the firefighters to evacuate the building, and firefighting operations must be carried on from safer outside positions.
ADDITIONAL INFORMATION FOR HOMEOWNERS
You might include additional topics, such as the following, in your public fire safety educational campaigns. The information might be part of public safety announcements, newspaper columns, seminars and open houses, or additional flyers.
Common Causes of House Fires
Some common causes of fatal fires, none of which were anticipated by the victims, include the following.
Your home is your refuge. Nobody who ever had a home fire really expected to have it. Statistically, your home probably will not have a fire; however, if it does, all must be prepared to act decisively to escape from the deadly environment.
1. Since this was written, a “monster house” in a Maryland suburb of Washington was destroyed in a daytime fire started by fireplace ashes placed in a paper bag outside the house.
FIRE-RESISTANCE RATINGS AND THE ASTM E119 FIRE ENDURANCE TEST
Fire Journal published an article by Erwin Shaffer, an official of the Forest Products Laboratory. The article sought to allay the fears of firefighters relative to the collapse potential of wood truss floors during a fire. It raised much protest from the fire service.
Shaffer relied principally on tests conducted in accordance with ASTM E1191, the standard fire-resistance test. Underwriters Laboratories rates truss assemblies tested to this standard as one-hour fire-resistive.
When I first found that ordinary apartment house fires were burning down into the floor void early into the fire and reported this as part of a study of “Combustible Multiple Dwellings” for the National Bureau of Standards (now the National Institute of Standards and Technology), one researcher exclaimed, “The fire is not supposed to burn that way.” My reply was, “Who put you in charge of how the fire burns?” The point is, test procedures should be realistic representations of actual fire conditions if the results are to be cited to reassure firefighters. Often, they are not.
Does ASTM E119 show this characteristic in the case of wooden floors of any kind? I think not, certainly not to such a degree as to reassure or add safety for firefighters. The following are noted in no particular order:
The 70-year-old standard time-temperature curve is not a valid measure of today’s fires.
In a 1975 bulletin, the Society of Fire Protection Engineers in discussing the fires in today’s contents said, “…. The rate of fire development can create a condition that may tax or overpower traditional fire defenses.”
In 1985, the National Fire Protection Association produced the remarkable film Fire, Countdown to Disaster. It shows the rapid growth of a typical very ordinary bedroom fire. Flashover occurs in TWO MINUTES AND 12 SECONDS; floor temperatures were 450°F. The carpeting can be seen burning. THIRTY SECONDS LATER, the temperature exceeds 1,230°F all over the room.
In 1980, The National Bureau of Standards (NBS) published “Fire Development in Residential Basement Rooms” (NBSIR 80-2120). Don’t be misled by the title. The rooms were typical living rooms or office reception areas. The fires were ignited in newspapers spread over the back of the couch. One figure shows a comparison of the fire exposure curve with the ASTM standard curve. The test curve peaks at over 1,000°C (over 1,800°F) in 10 minutes.
The report’s conclusions are noteworthy: “The rate of development and intensity of real fires involving the burning of typical furniture and interior linings in a room during the first 20 minutes may be significantly greater than those defined by the ASTM E119 standard time-temperature curve. A more realistic time-temperature curve for residential occupancies is presented in this report. This curve is considered suitable for testing exposed floor construction, floor-ceiling assemblies, wall assemblies, columns or doors.” Politics of the “kill the messenger” variety caused this recommendation to be abandoned. The Bureau of the Budget zero-funded fire research at NBS for several years, but Congress restored funds annually. The subject of the inadequacy of the standard fire test has not been revisited since.
A dramatic demonstration of the amount of fire the contents of an apartment can generate was seen on NBC news in September 1991. A two-fatality fire belched flames 20 feet out the windows of the 19th floor of a Los Angeles high-rise building. Tom Brokaw noted, “There were no sprinklers.”
(The ASTM E119 test is conducted in a tightly firestopped 14- 2 17-foot structure. This cannot be regarded as representative of structures built in the United States.)
The ASTM test structure is built by the organization sponsoring the test. It is obvious that the test structure is the best that can be built and is not the typical or average structure. The typical structure may have many structural defects. Firefighters fight fires in buildings as built, not in a world of perfect buildings and construction methods.
The size of the test structure is not realistic. The ASTM void might contain 238 cubic feet of air, which would contain about 50 cubic feet of oxygen. One cubic foot of oxygen provides 537 Btus. The 50 cubic feet would generate a maximum of 27,000 Btus, which would be provided by about 3.5 pounds of wood. The burning of the wood in the trusses is, therefore, self-limiting until the ceiling opens up to admit more air.
A realistic structure would be about 1,200 square feet. A greater amount of oxygen would then be available to support combustion. A realistic structure would have provision for additional air, representing the air that would be available through the alleged firestopping, which, as observed and photographed, is often ineffective.
The test incorrectly assumes that the fire will burn only upward. The test does not consider that fire can burn downward. As noted, today’s fires can burn down into the floor void in as little as five minutes.
The test does not simulate fire entering the truss void through the floor above.
The test does not simulate fire entering the truss void laterally, such as by an exterior fire burning through the combustible exterior into the truss void.
In Lake Benbrook, Texas, an exterior fire burned laterally into the void through the fascia board. The trusses were destroyed by fire passing through or around the firestopping.
The test does not provide for any penetrations of the gypsum sheath. Light fixtures, HVAC outlets, and ventilating duct inlets are typical of pinholes or other penetrations of the gypsum sheath.
The test does not simulate fires that initiate in the void, such as from wiring or metal chimney ducts. Fire can be directly delivered to the void by ventilation ducts from interior kitchens or bathrooms. A number of the fires investigated for the NBS started above or behind the gypsum board sheath.
The test was conducted with a static live load of 30 pounds per square feet. If the test results are to be used to reassure firefighters, it is reasonable that in addition to the static live load there should be a moving live load with some impact component representing two firefighters making a primary search for victims. Two firefighters, with modern lightweight SCBA and the minimum tools used for a search, weigh about 450 pounds.
The test is conducted under negative pressure. This exhausts toxic and explosive carbon monoxide that would be present in any real-life void space fire.
There is no evaluation of the extension potential presented by the vertical voids (such as for piping) open to the floor void.
Dick Sylvia, a fire officer and fire science instructor, wrote while he was editor of Fire Engineering an article on the hazards of truss floors. A representative of the National Forest Products Association wrote to argue that firestopping and education of architects could eliminate the hazard. The deficiencies of firestopping have long been noted and discussed.
Education of architects has been offered as a solution to many fire service problems. Imagine an architect, well aware of the problem of wood-truss construction, who would design firefighter-safe, yet necessarily more costly, buildings. That architect likely would have few commissions.
The fire service must take care of itself.
The above was abstracted from the comprehensive discussion of truss problems in BCFS3, Chapter 12. Chapter 6 discusses fire-resistance testing and the fact that the one-hour rating does not mean one hour in a real fire. Chapter 5 discusses combustible floor assemblies and the fallacy of assuming that nailing up gypsum board necessarily provides rated fire resistance. This is particularly noteworthy in the case of gypsum board top-floor ceilings nailed to roof trusses. There are NO rated triangular truss-gypsum board assemblies. I believe that there is a serious question as to whether the ASTM E119 test is adequate when used to determine the fire resistance of wooden structures.