By KENNETH MORGAN
We have all read about or heard of the dangers of engineered wood joists—or I-joists—when exposed to fire, but they don’t need to be on fire to degrade. Developed in 1969, I-joists have become a construction staple because of their economic value and ability to shoulder large loads over large spans. Originally constructed of a plywood web and solid flanges (chords), the flanges were replaced with laminated wood in 1977. The switch to orientated strand board (OSB) webs occurred in 1990.1
Just how much does it take to damage these engineering marvels? When exposed to heat, they degrade rapidly,2 so the importance of knowing the structures in your first-due response area becomes alarmingly evident.
An occupancy fire in Clark County, Nevada, in the early morning hours of March 5, 2009, was a reminder to the Clark County (NV) Fire Department of how even a small fire can place crews in imminent danger. This occupancy, constructed in 1992, was in an area of the county known for light commercial businesses that borders the City of Las Vegas and is on the southern edge of a larger complex of similar structures. It was of typical block wall construction with a flat roof and was split into two occupancies.
At 0422 hours, a caller advised the fire alarm office that there was an orange glow coming from under the garage door with gray smoke showing from a small, single-story commercial structure at 3111 S. Valley View Boulevard (photo 1). Because of the occupancy type, a second truck and a heavy rescue company were requested. A fire attack engine was assigned, and a second engine arrived and forced entry through the roll-up doors. In all, eight crews were called to the scene.
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| (1) A building similar to the fire building. (Photos by author.) |
Once crews gained access, they advanced a 1¾-inch line, advised Command of poor visibility and low heat, and requested ventilation to assist them in locating the fire. A truck company advanced to the roof to vent; the officer from the company used a thermal imaging camera (TIC) to attempt to locate a heat signature, but it indicated no hot areas on the roof other than at the base of a heating, ventilation, and air-conditioning (HVAC) duct. The company chose an area around the duct to open the roof, thinking that it may follow the HVAC ducting. There was no indication that the roof was compromised. Shortly after the fire attack crew made entry, the fire was found and easily extinguished. The smoke level began to dissipate, revealing a small debris pile (photo 2) consisting of some boxed textile material.
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| (2) The small fire. |
When the smoke cleared—enough to see to the interior roof—a horrific sight appeared. The roofing system was constructed of engineered I-joists, and many of the joists were completely compromised. Although the fire was confined to the pile of origin, the I-joists were severely degraded. In photo 3, the height of the flame can be noted on the wall. Photos 4 and 5 show the degradation of five adjacent I-joists over the fire, caused primarily by convected heat. Not only were the joists damaged, but the connections to the wall also were compromised; heat had attacked and degraded the roofing system. There is no notable alligatoring on the flanges, yet the webs over half of the joist span were completely gone (photo 6).
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| (3) The small fire and flame impingement to the wall. Note the joists circled above. |
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| (4) The heat pattern is evident. Notice that all of the web material is gone and that the heat was channeled along the entire joist area. |
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| (5) In the middle you can see the web material disintegrating because of the heat and the vent hole cut. Looking at the fire patterns, it appears there may have been fire there. On our arrival, there was no fire in the roof system, just some fire smoldering in the pile of textiles on the floor. |
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(6) Joist damage is evident over half of the span of the wall. |
This incident presented the indications of a small fire, but it held a secret that had the potential to kill firefighters. The crews learned and reinforced several valuable lessons that morning, which included the following:
- NO FIRE IS ROUTINE! Do not get complacent.
- The value of knowing the first-due area cannot be overstated. If this building had been identified as having an engineered roofing system, alternate, safer tactics could have been used, and no personnel would have been placed on the roof.
- It does not take much fire to make an I-joist fail; heat alone can do this. There is some indication of fire in the truss around the wall area, but the majority of the damage is strictly heat related.
- Consider identifying roofing systems and placarding the building so fire crews don’t have to guess what they are walking on.
- TICs did not help locate an area of concentrated heat. This roof was composite foam over plywood, which hid any heat signature. The lack of heat signature and no indication of compromise in the foam suggested a small fire and no involvement of the roofing system; this can give you a false sense of security. If the roof sheeting had been OSB instead of plywood, the roofing system might have completely failed.
REFERENCES
1. www.umass.edu/bmatwt/publications/articles/i_joist.html.
2. www.cdc.gov/niosh/docs/wp-solutions/2009-114.
● KENNETH MORGAN, MPA, EFO, CFO, MIFireE, is a 27-year fire service veteran and the deputy chief of operations for the Clark County (NV) Fire Department. He has a master’s degree in public administration and is a fire officer VI and a CFO designate. He has completed the National Fire Academy’s Executive Fire Officer program.
