On August 3, 1994, a Louisville firefighter plunged through a lightweight truss roof of a one-story concrete self-service storage building (mini warehouse) and died. The Louisville (KY) Fire Department prepared a comprehensive investigation report, and I am indebted to Fire Chief John B. Corso for providing a copy and giving permission to use the information for the benefit of the fire service.

The alarm office received several calls about this fire at 0347 hours. This certainly indicates a working fire and, at this early morning hour, all should think, “This fire has probably been burning for some time but has just now `shown up.`” Heavy smoke but not much heat was reported on arrival.

The roof was plywood with fiberglass composite shingles supported on typical lightweight triangular trusses, 24 inches on center.

The ventilation crew had opened the roof. The roof was not spongy; this characteristic usually is missing when the roof is trussed. The trusses hold together until they collapse “without warning.” The warning is in knowing the roof`s construction. The roof collapsed at about 0400 hours on the opposite side of the roof from the vent hole, and heavy fire erupted from the hole. One firefighter fell through it.

The circumstances of the collapse appear to be very similar to a house roof collapse in Phoenix, Arizona, in which three firefighters went through a burning truss roof.1

Unfortunately, the building layout was not typical. Usually, the storage bins are back-to-back and accessed through overhead doors from the outside. In some cases, however, access to the bins is through an interior corridor, and the bin openings face each other. The firefighter fell into the corridor. Two bin doors were open in the corridor and blocked the view of the fallen firefighter. It took 19 minutes to remove the firefighter, who was transported to the hospital, where he died.2

When a successful vent is made, the air supply to the fire increases (537 Btus are generated for each cubic foot of oxygen delivered to the fire). The structure may be deteriorating rapidly, and it is very dangerous to remain on the roof to admire your handiwork or to make another cut.

While it was not a factor in this case, firefighters working on the roof should have two separate means of egress. No roof was ever designed to be a firefighter`s working platform.


The author concludes in a summary that the critical temperature in the wood trusses was reached 18.75 minutes before the recorded collapse time. Based on numerous questions asked in seminars, it seems there is a widespread belief in the fire service that firefighters can remain safely in or on a structure fire for 20 minutes. My concern is that the 18.75 minutes, which I consider an invalid conclusion, is close enough to 20 minutes to give credence to the false and dangerous mythical “20- minute rule.”

The author discussed the “Standard Time Temperature Curve”–the curve specified for tests under ASTM (the American Society for Testing and Materials) E 119, without pointing out that it is the curve specified for tests and may have no relationship to any specific fire.

In fact, in 1980, the National Bureau of Standards (NBS, now the National Institute of Standards and Technology) published “Fire Development in Residential Basement Rooms” (NBSIR 80-2120). In those tests, the temperature peaked at more than 1,8007F in 10 minutes. The fire report indicates that there was a high fire load in the fire building, possibly much higher than in the NBS tests, which represented a typical basement recreation room or living room.

Conclusions of the NBS report 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 E 119 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.”

Unfortunately, improving the 1916 ASTM E 119 standard would throw the manufacturers of fire-resistive components into confusion. Shortly thereafter, the Reagan White House, in a typical political “kill the messenger” scenario, made a determined effort to wipe out (zero fund) fire research at the NBS and only strong congressional efforts backed by most of the fire protection community preserved it. All our fire-resistive ratings are based on a standard shown to be too weak.

It is simply not valid to use the standard time-temperature curve as a constant in an analysis of any specific fire.

The ASTM test is conducted usually with an evenly distributed static load of 30 to 40 pounds per square foot. Three firefighters on the roof represent a dynamic load of several hundred pounds over a small area. In addition, the impact load of moving around; cutting the roof, even with a chain saw; and removing the covering is severe, though never determined.

The author assumed that the gusset plates would continue to hold under the load until char reached the tip of the gusset plate prong (“penetration depth 0.46875”). This is certainly questionable. By conduction, the heat would be delivered from the prongs to the wood fibers under tension, which are gripping the prongs. These vital fibers could be destroyed by pyrolytic decomposition before the char reached the same depth from the surface.

I have observed many cases where trusses do not have the required depth of penetration. Mishandling trusses on the construction site loosens gusset plates, as does hammering by tradepersons installing equipment. Such trusses would fail even earlier than perfectly built trusses in mint condition.

Firefighters would be well advised to place more credence in the tests conducted by retired Battalion Chief John Mittendorf of the City of Los Angeles (CA) Fire Department, which showed collapse in three to four minutes. The fire was not standard but typical, and there was no superimposed load on the structure, a bias in favor of the structure.3 RECOMMENDED SOP: Firefighters should not be under or on any truss involved in fire. For further information, see Building Construction for the Fire Service, Third Edition, Chapter 12, “Trusses.”


As a result of the 1988 Hackensack auto dealership truss collapse, which killed five firefighters, New Jersey requires signs on the exterior of buildings indicating truss roof or floor construction. The sign is a triangle with the letter “R” or “F” or both in the center.

I recognize that some trusses are better than others. A Bob Evans restaurant at Breezewood on the Pennsylvania Turnpike has solid wood trusses, pinned with wooden “trunnels” (no metal) supporting a heavy plank roof. Such a roof would be a very occasional exception to the general rule.


An article in the food section of the local paper described what reporters found when they looked into people`s refrigerators. One common item was valuable papers, such as drafts of professional publications, stored in the refrigerator “because it was the most fireproof place in the house.” We`ll talk about this seriously mistaken idea in the future, but I would appreciate hearing stories of valuable documents lost because they were stored in “fireproof” tin boxes or whatever. n


1. The Phoenix Fire Department has produced an excellent videotape of this spectacular fire at reasonable cost. Write to: Phoenix Fire Department, 455 N. 5th Street, Phoenix, AZ 85004.

2. The Fort Worth (TX) Fire Department was deceived by a steel storage building that backed up to a hill and thus the rear units were accessible only from the corridor. The fire extended to a number of units before it was stopped. Examine mini storage units in your area for interior corridors. Departures from customary layout should be noted on the prefire plan.

3. Mittendorf, John. “Lightweight Construction Tests Open Fire Service Eyes to Special Hazards.” Western Fire Journal (now American Fire Journal), January 1982, 23.

FRANCIS L. BRANNIGAN, SFPE, a 55-year veteran of the fire service, began his fire service career as a naval firefighting officer in World War II. He`s best known for his seminars and writing on firefighter safety and for his book Building Construction for the Fire Service, Third Edition, published by the National Fire Protection Association. Brannigan is an editorial advisory board member of Fire Engineering.

No posts to display