Chemical Risk Assessment and Prevention
Coal Power Plant Stack Fire
A 1000-foot high stack to control emissions from a coal-fired power plant caught fire while under construction. While the outer support for the stack was made of non-combustible concrete, the two inner stacks or "liners" were being made of fiberglass reinforced plastic or FRP, which was known to be a flame propagating material. Large-scale fire tests in the 1970s showed that FRP liners could reach temperatures over 1500° F in less than a minute if an igniting fire was present and would be completely burned through in about four minutes.
In this stack project, the first of two liners was about half way completed up the stack when torch cutting was performed on the very top of the stack. Unfortunately, the torch cutting was done without a hot work permit (none was ever produced) or a proper fire watch. During the investigation by Dr. Fox, incidents at other stacks were discovered in which hot work performed at a high distances up a stack provided the ignition for fuel near the bottom of the stack. In fact, during the cleanup after this stack fire, torch cutting at the top of the stack was reported to have ignited combustible debris at the bottom of the stack. Therefore, while there were other potential ignition sources, the unattended hot work was determined to be the most likely ignition source. The hot work was the only out-of-the-ordinary activity that took place just prior to the fire. The reports of hot work causing fires at considerable distances (top vs. bottom of stacks) were important to counter the general belief that burning materials from hot work at or near the top of the stack would extinguish and/or cool and not be capable of igniting a fire by the time it reached the bottom of the stack.
At a lower level in the stack, the 60-foot sections of the liner were joined together using grinding, fiberglass and fresh, uncured resin. The freshly applied resin is considerably more flammable than cured resin. To maintain the temperature needed for curing, the joints-in-progress were enclosed with flammable plastic sheeting. While there were a number of fuels that could have been ignited, the plastic sheeting was the most likely first fuel ignited. Simple tests showed that once ignited, the plastic sheeting produces raindrops of fire that would have contributed to the rapid initial spread of the fire. This observation was also consistent with the MSDS for the plastic sheeting that warned to keep the sheeting away from ignition sources. The second choice for the fuel first ignited was the FRP dust created by the grinding.
Per eyewitness accounts, the origin of the fire was inside the liner where the 60-foot long sections were joined. As noted above, the most likely initial fuel was the extensive amount of flammable plastic sheeting. However, the major fuel for the large hostile fire that followed (after the sheeting) was the cured and uncured portion of the FRP liner.
A foreman who went up a man-cage to investigate the initial fire died in the incident. He most likely had decided to take a man-cage up to the top of the stack to rescue three workers stranded up there. However, he had no training or appreciation for how rapidly the FRP liner would burn out of control. For example, it took 7-minutes for the man-cage to go from the bottom of the stack to the top, but only 1-minute for the temperature inside the liner to reach 1500° F. This was clearly an ultra hazardous situation that required the utmost in fire protection safety with special emphasis on early warning and emergency egress. The only egress for the foreman was the slow-moving man-cage. There was no other egress. There was no evidence that a comprehensive fire hazard evaluation had been performed prior to or during the construction.
It is important to distinguish between the initial fuel source, most
likely the plastic sheeting, and the major fuel that caused the death,
injuries and structural damage. The FRP liner presented a significant
amount (over 160,000 pounds) of combustible fuel (cured resin) and flammable
fuel (uncured resin and wax) with a large surface area.
While the mechanics of how and where the fire itself started were important, the "root cause" for the large hostile fire was found in the history of events leading up to the large hostile fire, including the selection of FRP for the liner material. The "root cause" is not always physical, as human factors, decisions made or not made, actions taken or not taken, negligence, greed, and code violations play pivotal roles. By way of analogy, a bullet might be the physical cause of a death, but the root cause would be how and why the bullet was aimed and fired.
Dr. Fox studied this fire in excruciating detail and provided deposition testimony. It was a 4-year investigation. The case settled within the first couple days of trial.
Dr. Fox is a fire expert, explosion expert and chemical expert with extensive experience in OSHA, EPA and DOT chemical regulations and chemical safety.
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