Responding to industrial ovens
Michael E. Petrie
Loss Prevention Consultant
Factory Mutual Engineering
West Mifflin, Ohio
“Responding to Fires in Industrial Ovens” by Bill Gustin (May 1999) is an excellent article and demonstrates the extreme hazards facing today`s firefighters at industrial occupancies.
Gustin mentions the need for pre-ventilation, but it is important to point out that pre-ventilation (purge) times vary with each oven. One of the first questions we as loss control engineers will ask when confronting a new oven is, “What is the purge time of the oven prior to setup?” In Gustin`s example, the oven was 100 feet long. In this case, if the oven operator were to respond that its purge time is 20 seconds, the firefighter had better take a second look at the operator`s statement. Purge times vary, but with an oven this size a total of four complete air changes will probably take much longer. For instance, such ovens could have a total purge time of many minutes to more than an hour, depending on the ventilation capacity. It is important to keep this in mind when such ovens are operated. Otherwise, you may be responding to an explosion instead of a fire.
Gustin mentions combustion safeguards that are designed to prevent an explosion involving the fuel to fire them (e.g., natural gas and propane). These include high- and low-gas pressure switches, combustion fan interlocks, flame verification, and safety shutoff valves. More common than not, I find that the property owner is not testing these components to the appropriate frequency. In addition, once I make a recommendation, it is later found out that one or several of the components failed. When responding to an incident, firefighters should not rely on the safety shutoff valves as the sole means of stopping the flow of gas to an oven or furnace. It is not uncommon for safety shutoff valves to leak excessively. Normally, a manual ball valve is provided on the incoming gas line and should be turned to stop the flow of gas.
