BACK TO ARCHIVES

General warehouse in New Orleans, Louisiana on March 21, 1996.

THIS MASSIVE warehouse fire burnt for six days before being brought under control by the New Orleans Fire Department. The damage, which was caused by an arson fire and a subsequent electrical fire, could possibly have been avoided. Complications involving the sprinklers were to blame, according to the NFPA.

The 380 m by 278 m large warehouse and distribution facility stored closeouts and discontinued items in two rack areas. The building structure consisted of unprotected steel I-beam columns and girders, and roof support was provided by unprotected metal bar joists. The roof was constructed of a single-ply membrane with rigid insulation over a corrugated metal deck. Part of the building was an office area and segregated storage area that occupied 19,021 m². The roof over the main warehouse was on two levels. The lower level ranged from 11m to 12m. The upper level, which covered the higher of the two rack areas, had a maximum height of 22m. The main warehouse floor, which measured 86,400 m², did not have any fire separation barriers.

On the south side commodities were delivered by truck, on the north side, they shipped out. In the east sections of the building there was a low portable rack storage area. These racks were not equipped with any in-rack sprinkler systems. The ceiling was 22m high in this area. In the middle of the building were high-bay rack storage areas. The racks in these areas were 19m high, 31 m long and 1.2m deep. There was a mixture of commodities stored on these racks, including: wicker baskets and furniture; rugs; polyfil pillows; cardboard boxes; duvets; towels; stacked plastic chairs and plastic bags. In addition to the racks, the main warehouse area housed a variety of conveyor systems and a mechanized retrieval system.

The building was equipped with 30 overhead sprinkler systems and 17 in-rack sprinkler systems. The facility was supplied by a 10 " looped water main connected to a 20" municipal water main. A 1,135,600 litre water tank provided an additional water supply. Two 9,462 litre/min fire pumps, one electric and one diesel, were connected to the fire protection system. The electric pump was connected to the water mains and the diesel pump was connected to the water tank.

The sprinkler system over the area of the first fire was designed to supply a density of 18 litre/ min/ ml. However, there were no in-rack sprinklers in this area. The ceiling was located about 22m above the floor and 16m above the highest level of racks.

A fire alarm system monitored the sprinkler systems, valves and fire pumps. Alarm and trouble signals were transmitted to an on-site security office that was continually monitored. Alarm signals were transmitted to an off-premises supervising station that was responsible for notifying the fire department. At the time of the first fire, there were 15 employees in the building.

The first fire, reported at 5.32am, quickly involved the combustible materials being stored in the 6.4m high portable racks. When the fire was discovered, it was reported to have fully involved the three-tier rack, and was extending to the ceiling. The rapid fire spread can be attributed to the combustible nature of the products being stored and their storage configuration. Employees tried unsuccessfully to fight it using portable fire extinguishers and occupant-use fire hoses. The overhead sprinkler system, that was located approximately 15m above the top level of the racks, activated at 5.32am, but did not extinguish or control the fire. The fire was extinguished by the fire department using an interior attack.

The New Orleans Fire Department responded at 5.37am with an initial attendance of six appliances. The first appliance arrived at 5.40am and reported heavy smoke showing. Eight additional units were dispatched at 5.42am. The fire was reported to be coming through the roof at 5.43am. Firefighters began an interior operation to contain the fire. It was declared under control at 8.44am, and extinguished at 11. 54am.

Once fire control had been achieved, all the sprinkler systems in the facility were manually shut down by closing the individual valves on the risers. According to the New Orleans Fire Department, this was because numerous sprinkler heads had opened throughout the warehouse, causing extensive water damage. At 2.20pm, electrical power was restored to the conveying system within the racks in the south-central portion of the building. Damaged wiring in this area arced and ignited combustible materials. As soon as the second fire was discovered, facility personnel began opening the recently shut valves on the ceiling and in-rack sprinkler systems. The catastrophic damage that followed is attributed to the fact that the sprinkler systems were shut down throughout the entire facility. Consequently, the sprinkler system was overwhelmed, and the fire department had to mount a defensive operation.

This second fire was declared under control on Wednesday, 27 March 1996 at 9.08pm, six days after the first fire.

The warehouse and distribution portion of the building, and its contents, were totally destroyed by the second fire. There was minimal fire and water damage to the area located on the other side of the fire separation wall. There was some structural damage to the walls due to the stresses placed on this portion of the building by the collapsing roof on the east side of the fire separation wall. On this side, structural collapse was widespread.

The devastation caused by the fires was the result of a number of factors, including:
excessive clearance between the ceiling sprinklers and the top of the storage racks in the area of fire origin for the first fire, lack of in-rack sprinkler systems ,shutting off all the sprinkler systems in the building following the first fire restoration of electrical service without evaluating the damage to the electrical system. This action was determined to have caused the second fire.

The results of the FRAME calculation for this case are:
the area factor g = 8.61
the initial risk Ro = 18.87

R = 3.17 , R = 0.94 , R = 1.50 : the property is NOT adequately protected, but the risk for the occupants is acceptable

With this case study three features of the FRAME method and program can be illustrated:

First, the results of the calculation (and the fire itself) show that the building is not adequately protected, although it is equipped with sprinklers. FRAME has a built-in balance between risk factors and protection, which makes that very large compartments with high fire loads are not considered as acceptable, even with sprinkler protection.

Second, the user of the program will not be allowed to introduce the 22 m value for the ceiling height, as the program accepts only a 15 m maximum. There are two technical reasons for this limitation : one is that sprinkler activation will be delayed and sprinkler protection can become ineffective when there is too much clearance between the ceiling and the fire seat, as this case illustrates dramatically. The second reason is that in such high spaces like in atria, stratification of the smoke layer can occur, making smoke detection, smoke venting and sprinklers ineffective. By refusing values above 15 m for the ceiling height, the program makes the user aware of the fact that he is confronted with a special situation where particular care is required in the design of the fire protection.

The third interesting feature is that the value of Ro gives the designer an early warning that the risk is too large to be properly protected . Very large risks shall be provided with redundant protection systems, which means in practice that the building has to be divided in compartments ans sprinklered as well.

For this particular case, the report as publicised in Fire Prevention (UK) issue 300 of June 1997, expressed concerns about the Sprinkler system performance, as it was not designed according the requirements of the NFPA codes.

The sprinkler systems never had a chance to control the second fire because the main control valves were shut off after the first fire was extinguished. A sprinkler system's ability to control a fire is greatly reduced if it cannot operate during the initial stages of fire development. By the time the second fire was discovered and efforts were made to open the valves, the fire had grown to a size where the sprinkler discharge would not have been effective.

While properly designed, installed and maintained sprinkler systems have an excellent record of controlling fires, it can be necessary to employ a more comprehensive fire protection plan, which accounts for uncertainties, when extremely large values are at stake. This is exactly the intention of the built-in balance of risk factors in the FRAME method.

System impairment
During overhaul operations, all of the ceiling and in-rack sprinkler systems throughout the building were shut down, despite the fact that fire damage was limited to a relatively small area in the north-eastern portion of the building. According to the fire department, it was necessary to shut off each riser because a number of sprinkler heads had opened throughout the facility following the first fire.
As the electricity was restored, the second fire broke out in an area remote from the first and there was no water in the sprinkler systems to control it. The fact that each sprinkler system was shut off individually contributed significantly to the resulting destruction of the building.

Utility Restoration
The restoration of electricity was done before the electrical system could be fully evaluated for damage, and before the sprinkler system was made operable. Failure to isolate or repair the damaged section prior to restoring power was another key factor in contributing to the ignition of the second fire. It is imperative that services are restored in a planned and coordinated manner, and only after a complete survey of the damage has been taken. There are several hazards associated with an uncoordinated restoration of utilities. The potential risk to rescue personnel and other workers operating in the area during overhaul and restoration is significant. Utility systems that have been damaged during a fire should be inspected and repaired before being restored. It is also imperative that everyone involved with the overhaul and restoration operations be aware of what actions are being taken by the different agencies and services involved.
BACK TO ARCHIVES