Our last column discussed a growing concern among fire departments about conducting offensive fire fighting operations at industrial properties where everyone was safely out of the building. We cited National Fire Protection Association (NFPA) 1500 Standard on Fire Department Occupational Safety and Health Program which statesin A.8.3.2: "We will risk our lives a LITTLE, in a calculated manner, to save SAVABLE property."
We stated that there is considerable discussion surrounding what is savable. A primary purpose of this series of articles, since inception, has been to help facility managers and fire departments analyze their risks through pre-fire planning. Our basic premises is that facilities that are properly protected, which for the purposes of this article means with adequate sprinklers, are usually savable. Guidance on determining what is adequate has been presented in past articles. A property loss prevention or fire protection engineer may need to be engaged to determine the adequacy of the sprinklers.?
This article will focus on general commodity warehouses because they are common to many industrial facilities and because they have been responsible for much of the discussion on offensive fire fighting operations. Hazardous materials warehouses will be addressed in the next article.
Adequate sprinklers are the main line of defense against a warehouse fire. If there are no sprinklers, or if the sprinklers are not adequate for the hazard, the warehouse is likely not savable if the fire has been burning for more than a few minutes before water from hose streams can be applied. Water generally cannot be applied this quickly, even if the fire station is next door. It simply takes too long to detect the fire, notify the fire department, respond, and then deploy hose streams.
Warehouse sprinkler designs are based on a relatively severe single point ignition scenario. The design is intended to keep structural steel temperature below its failure temperature and to limit fire spread. Details on what "limited" fire spread means have varied slightly over the years but generally means on the order of a few hundred square feet or less. Multipoint ignition could overwhelm even an adequately designed system.
Current sprinkler design anticipates that automatic smoke and heat vents are not provided. A complete discussion on this highly controversial issue can be found in the Fire Protection Handbook published by the National Fire Protection Association. ???
Warehouse sprinklers are broadly broken down into control mode sprinklers and suppression mode sprinklers. Control mode sprinklers are intended to stop the growth of the fire. The fire may still burn at the heat release rate it reached when fire growth was stopped. Major offensive fire fighting operations are anticipated, which is why a hose stream allowance of usually 500 gpm (1900 l/min) is made. This allows for two 2.5-inch hoses (65 mm) to be used for final extinguishment.
Suppression mode sprinklers not only stop the growth of the fire but are intended to significantly reduce the heat release rate. Final extinguishment by the fire service is still needed but this is frequently more of an overhaul type of operation than an aggressive fire fighting operation. A 250 gpm (950 l/min) hose stream allowance is made for this final extinguishment.??
There has been interest in developing an extinguishing mode sprinkler that does not require the fire service to perform final extinguishment, but such a sprinkler is unlikely to be common for quite some time.
Some of the biggest issues in warehouse fires are:
- Visibility. Associated with this is wayfinding, which means finding the way to the fire and also back out.
- Size. Facilities of one million square feet (100,000 square meters) are not uncommon and there are even larger facilities. Associated with this is air management, meaning having enough air left in the breathing apparatus to do work by the time the fire area is reached and before it is time to back out again.???
- Access. Rack storage to 35 feet (10.7 meters) high is extremely common and rack storage up to 100 feet (30 meters) high exists. There are a number of complex storage arrangements that make it very difficult to get water to the seat of the fire.
Visibility is an issue because the smoke is cooled by sprinkler water which causes it to lose buoyancy. This means it will not rise and may not even be exhausted through vertical ventilation openings. In the immediate area of the operating sprinklers, the downward thrust of the sprinkler water can entrain smoke and drive it to the floor. Unfortunately, in order to improve visibility, firefighters are often tempted to shut off the sprinklers to let the smoke lift or to let it "light up" so it can be seen. This has resulted in the loss of many warehouses. Massive horizontal ventilation by removing large sections of the exterior wall has also admitted enough air to cause warehouse fires to grow out of control.
What can be done then? First of all, thermal imaging cameras are a necessity. Each crew should have one. Proper training on the interpretation of the images is also critical. In the opinion of this author, gradually introduced and carefully monitored mechanical ventilation - or natural ventilation through openings that can be closed - is the proper way to manage the smoke. The main reason is that ventilation can be stopped if it is exacerbating the problem. If a large wall section is removed and the fire starts to grow, there is not much that can be done. If a mechanical fan starts to cause fire growth, it can be shut off.
Because of visibility issues, it is critical that the firefighter can find his/her way back out. Hoselines, lifelines or other methods are essential. Ideally, a properly trained and equipped plant employee can escort the fire service to the area of the fire.
Significantly more smoke should be expected with control mode sprinklers than when suppression mode sprinklers or where in-rack sprinklers are present. Smoke conditions can range from total loss of visibility in a smaller warehouse with control mode sprinklers and plastic products to a light haze in a large warehouse with in-rack sprinklers or suppression mode sprinklers.?
Size: The fire could be several hundred feet from an exterior access door. Fire service personnel should have practice stretching hose lines in large facilities. Standard thirty minute breathing apparatus may not provide an adequate working time. Longer duration units should be considered. Experience has shown that even in adequately sprinklered warehouses, a significant supply of breathing apparatus bottles will be needed. One fire at a very large warehouse that operated just four sprinklers and needed only 1?-inch (45 mm) hose lines for overhaul still required nearly 50 air cylinders. Dispatch an air supply truck.????
Air management practices described in the fire service literature such as the text Air Management for the Fire Service should be implemented. Working until the low air alarm sounds might not allow enough time to get back out before the air supply runs out. Fire departments that serve tunnels or subways seem to have long duration breathing apparatus and air management practices. Large warehouses have the same needs.
Access: Access problems can be vertical (getting to a fire 60 feet (18 meters) up in a rack), horizontal (getting to a fire in a large pile) or compounded by complex storage arrangements such as carousels. Details on how this will be done should occur in the pre-planning phase. Even the seemingly simple process of using forklifts to unload commodity for overhaul should be pre-planned. Will firefighters operate the forklifts or will facility employees wear breathing apparatus?
More complex plans, such as firefighters gaining access via stacker cranes should be practiced. Carefully evaluate the ability of the stacking vehicles to operate under fire conditions.
Many other potential problems and hazards exist such as commodity collapse and high water main pressure. These issues have been addressed in previous articles. This article focuses on the issues that seem to be present when the fire service encounters severe operational difficulties in warehouses.?????
If the above issues cannot be resolved to the satisfaction of the fire chief or facility management, even an adequately sprinklered facility could be lost if the fire service cannot overcome these issues. This potential should be known before the fire so that plans for the loss of the warehouse can be made. Solutions to these issues will be discussed further at a conference in February 2010 and reported in a future article.???????????????????????????????????????????????????????????????????????????
Feel free to contact this author at John.Frank@xlgroup.com or at (404) 431-2673.
John Frank, P.E., CFPS is with XL GAPS, a leading loss prevention services provider and a member of the XL Capital group.? "XL Insurance" is the global brand used by members insurers of the XL Capital Ltd. (NYSE: XL) group of companies. More information about XL Insurance and its products is available at www.xlinsurance.com.