Probing Warehouse Hazards
Some products don'treadily lendthemselves to acommodityclassification test. Alarge scale test isneeded.
Volume 22, No. 6
During pre-fire planning tours of warehouses, I have frequently heard firefighters state that they did not think that sprinklers could control a fire because of high fire loading, high ceilings or other factors. NFPA 13, Standard for the Installation of Sprinkler Systems, FM Global Data Sheet 8-9, Storage of Class 1, 2, 3, 4 and Plastic Commodities, and other 8-series Data Sheets provide extensive guidance on warehouse fire protection based on nearly forty years of fire tests at FM Global and Underwriters Laboratories (UL). But even with this testing, situations continually arise where these documents do not answer the question of what sprinkler protection is needed.
In these cases, the aforementioned laboratories can be used to determine the needed level of sprinkler protection. This article focuses on some of the research that Swiss Re Global Asset Protection Services is conducting at Underwriters Laboratories to answer some of these questions.
Some of the tools available are:
- the large fire products collector.
- the large scale test facility.
- fire modeling software.
- the Actual Delivered Density (ADD) apparatus.
The first two tools can provide stand-alone answers. The last two are currently used for screening or as part of an iterative approach in conjunction with the fire products collector or full scale fire tests.
The large fire products collector (figure 1) is a 10 megawatt scale calorimeter that measures heat release rates from burning commodities with different rates of water application. The affect of the water application on the heat release rate is compared to "benchmark" commodities and a commodity classification (for example a Class III commodity) is assigned. Once the commodity classification is known, the guidance in NFPA 13 or FM Global Data Sheet 8-9 is applied.
Some products don't readily lend themselves to a commodity classification test and a large scale test is needed. The fire products collector may still be used for screening to help set up the large scale test.
Large scale fire tests are used when a conclusive answer cannot be obtained from the fire products collector, or when information such as the affect of sprinkler obstructions on fire suppression or the affect smoke and heat vents on sprinkler activation is needed. Because large scale fire tests are expensive, screening is often used to help ensure that a sprinkler protection scheme that has a high probability of success is selected.
Besides using the fire products collector for screening, fire modeling (figure 2) and the ADD apparatus (figure 3) can also be used. Fire models can evaluate the affect of a higher ceiling, different aisle spacing or a faster fire growth rate. This can in turn help predict the sprinkler arrangement that is likely to be successful in full scale testing. As of this writing, fire modeling cannot be used by itself to determine the needed sprinkler arrangement in a warehouse. Research to improve the predictability of fire models is ongoing. Figure 4 shows a schematic describing research into sprinkler water droplet behavior.???
Swiss Re Global Asset Protection Services is currently using the UL ADD apparatus to investigate obstructions to Early Suppression Fast Response (ESFR) sprinkler discharge. Earlier tests at FM Global indicated that obstructing the discharge to ESFR sprinklers with trusses, bridging elements, lights, etc., could result in complete loss of control of the fire with resulting loss of the warehouse. Such fires are generally well beyond control by manual fire fighting and will almost certainly result in major structural collapse.
There are, however, many existing warehouses that do not fully comply with current obstruction rules, yet do not have obstructions that are as severe as initially tested. Making the changes needed to comply with the obstruction rules could cost hundreds of thousands or even millions of dollars. Although the ADD apparatus cannot by itself determine if an obstruction is acceptable, it can help determine if a full scale test of the obstruction is likely to be successful. Figure 3 shows representative ADD testing output.?
As of this writing, 100 ADD tests have been conducted along with three full scale tests. The three full scale tests investigated a specific obstruction scenario and indicated that suppression could be achieved for this specific warehouse scenario.
The use of the tools outlined in this article can help answer questions about storage arrangements that are not defined in current fire protection standards. This gives the municipal or industrial firefighter assurance that fire protection that complies with existing standards or that is developed based on fire testing will protect the facility, occupants and? firefighter.????????
Questions can be directed to the author at John_Frank@swissre.com or (770)389-1480.???????????????????????
Swiss Re is the world's leading and most diversified global reinsurer.