Article

Combustible Storage

Improperly stored oxidizers can pose a fire risk in warehouse occupancies. 

by Ed Comeau and Robert Duval

The following article appeared in the November/December issue of NFPA Journal.  Reprinted with permission.
© 2001 NFPA Journal

On August 2, 2000, Phoenix, Arizona, experienced one of the largest fires in its history in a multi-tenanted building containing Central Garden and Pet Supply and Cardinal Distributors. By the time fire crews extinguished the blaze the next day, the building was a smoldering ruin. A number of civilians had to be evacuated from the surrounding neighborhood, and the loss is estimated to be in the hundreds of millions of dollars.

What caused the fire to become so large? NFPA sent Senior Fire Investigator Robert Duval to Phoenix to find out. Investigation into the cause of the fire continues as of this writing.

The fire department

The 20-year-old building in which the fire started contained two occupancies separated by a concrete panel wall that extended from the floor of the building to the underside of its roof deck. On one side of the wall, with multiple fire door penetrations, was a home and garden supply warehouse containing a variety of products and commodities. On the other was a pharmaceutical supply warehouse.

The main portion of the building measured 400 feet (122 meters) by 208 feet (63 meters). The section occupied by the home and garden supply operation measured 220 feet (67 meters) by 208 feet (63.4 meters), and the pharmaceutical distribution area was 180 feet (55 meters) by 208 feet (63.4 meters). The building, which would be classified as a storage occupancy by the 2000 edition of NFPA 101®, Life Safety Code®, also had an office wing 105 feet (32 meters) long and 30 feet (9 meters) wide.

The exterior walls of the warehouse had no windows, though the office wing did. Overhead doors through which stock was loaded and unloaded were on the east side of the building.

The structure’s roof assembly consisted of a 1/2-inch (1.3-centimeter) plywood deck covered with many layers of mopped asphalt and supported by 10-by-4-inch (25-by-10-centimeter) purlins supported by engineered laminated beams. The beams were supported by steel columns 5 inches (13 centimeters) in diameter on a 40-by-23-foot (12.2-by-7-meter) spacing. In the warehouse, the ceiling was 30 feet (9 meters) high.

The exterior walls were tilt-up concrete panels, 6 inches (15 centimeters) thick, attached to the concrete floor slab with threaded connections.

The building was equipped with an automatic fire sprinkler system. The pharmaceutical warehouse and home and garden supply warehouse had ceiling-level systems with .495 gpm/feet2 over 2,000 square feet (186 square meters) with sprinklers rated at 286˚F (141˚C) with orifices 17/32 inch.  There were no in-rack sprinklers.

Building contents

Because the warehouse supplied area home improvement stores, the products offered varied significantly, from bird feeders and tools to redwood products and batteries. Also among the materials were fertilizers, insecticides, and pesticides. They were stored in different configurations, on double and single-row racks, and in solid piles 10 to 20 feet (3 to 6 meters) high. The solid- and open-shelf configurations were 20 feet (6 meters) high, separated by aisles 8 to 10 feet (2 to 3 meters) wide.

Many items were stored in corrugated cartons scattered throughout the warehouse wherever space allowed. Some pallets were encapsulated in plastic sheathing.

Chlorinated pool chemicals, which are oxidizers, and are addressed in NFPA 430, Storage of Liquid and Solid Oxidizers, were also stored in the warehouse. While not combustible themselves, oxidizers can significantly increase the intensity with which other products burn. Furthermore, they’re incompatible with other products that may be stored in home and garden occupancies.

Oxidizers are divided into four classes based on the inherent hazards they present. Class 1 oxidizers increase the burning rate of other products slightly. Class 2 oxidizers moderately increase the burning rate and can cause spontaneous ignition. Class 3 oxidizers severely increase the burning rate of other products, can cause spontaneous combustion, and will undergo self-sustained decomposition. And Class 4 oxidizers severely increase the burning rate of other products, can cause spontaneous combustion, will undergo self-sustained decomposition, and will cause an explosive reaction.

When contaminated with incompatible products, oxidizers can cause spontaneous combustion. If the heat of combustion is confined, nearby combustibles may ignite. To suppress fires involving oxidizers, large amounts of water may be required. Small amounts of water can cause oxidizers to react and release chlorine gas.

The fire

On the day of the fire, employees reported an unusually strong chlorine odor in the home and garden supply side of the warehouse. Chlorine could often be smelled in that area because many of the products stored there contained the chemical, but this was worse than usual. To identify the source, the employees moved pallets of the pool chemicals outside and opened several large overhead doors to help ventilate the building. At 11:30 a.m., the chemicals were moved back into the building, but the chlorine odor became strong again, so all of the pace tri-chlorine in 35-pound (16-kilogram) plastic buckets and some pace tri-chlorine in 75-pound (34-kilogram) fiber drums were taken outside to the east side of the building. None of the cal-hypo or pool shock was removed from the building. The work day ended before workers discovered the source of the odor.

Less than an hour later, pharmaceutical supply company employees on the other side of the building reported hearing a rumbling noise. Some thought it was a thunderstorm and went outside to look. When they did, they could see smoke coming from the other side of the building.

Driving along the nearby freeway, a deputy chief from the Tempe, Arizona, Fire Department also saw the large column of smoke and immediately reported it to the Phoenix Fire Department. He then drove toward the smoke to find the source. At about the same time,  Fire Station 23, located near the warehouse, also began responding after a civilian notified crews of the blaze. The sheriff’s department was also notified by two sheriffs, who saw the column of smoke.

The Tempe chief arrived on the scene at 5:01 p.m., assumed command, and reported a working fire in the warehouse. Shortly after, Engine 23 arrived and positioned itself at the southeast corner of the building after connecting to a nearby hydrant. Because the fire was so intense, firefighters immediately began applying water using an engine deluge gun.

At this point, the fire was well-involved, and fire crews reported that the overhead doors were beginning to buckle and that the fire’s thermal column was lofting debris into the air. Crews noted that breathing apparatus was unnecessary because the smoke was going straight up but the smoke came back down and firefighters on Engine 23 were sent to the hospital and treated for smoke inhalation.

As the fire grew, flames ignited contents of the exterior storage area, so firefighters advanced hand lines in an attempt to control these fires.

At 5:03 p.m., the incident commander issued a second alarm. The Phoenix Fire Department, which comprises 52 stations spread out across 480 square miles (1,243 square kilometers), is part of an automatic aid system that includes 19 other cities. Two minutes after the second alarm was called, Engine 272 arrived from Tempe and began applying water using its telescoping water tower.

At 5:07 p.m. Engine, Rescue, and Ladder 22 arrived and were positioned on the west side of the building. The crews reported that the tilt-slab walls were leaning outward and that there was a significant danger of collapse.

The incident was upgraded to a third alarm at 5:11 p.m.

At 5:17 p.m., a section of the tilt-slab walls in the southwest corner of the building began to collapse, pulling other sections along with it. Aerosol cans began to rocket out of the building towards firefighters. The crew from Ladder 22 reported hearing several cans strike their apparatus.

To protect them from the potentially lethal effects of the burning chemicals, all personnel were ordered to don self-contained breathing apparatus at 5:29 p.m., and civilians in the area were evacuated. In addition, the nearby freeway and local roads were closed. Firefighters on the scene had to be decontaminated because of their contact with the smoke.

The aftermath

Following the fire, five firefighters suffering from the effects of smoke inhalation and extreme heat—on the day of the fire, the temperature hit 100ºF (38ºC)—were hospitalized for observation. According to the Arizona Department of Health Services (ADHS), 10 area residents also sought treatment at local hospitals.

ADHS took several air and dust samples from the fire scene and from residences downwind of the fire. No significant pesticide depositions were found in any of the homes.

Fire department investigators, trying to determine the cause of the fire, were hampered by the heat, which was normal for Phoenix at that time of year. They had to work early in the morning, before it became too hot to operate. To add to their discomfort, they had to wear hazardous materials suits and breathing apparatus to protect them from the hazardous materials stored in the warehouse.

Investigators still haven’t determined the cause of the fire, but they theorize that one of the stored commodities, such as the pool chemicals, played a significant role in the spread of the fire.

Based on this and other fire investigations and analysis, NFPA has determined that the following factors may contribute to large loss in similar facilities, including lack of segregation between incompatible materials, such as oxidizers and hydrocarbon based materials, lack of proper storage configuration for oxidizers, and inadequate sprinkler protection for commodities in a warehouse.

This wasn’t the Phoenix Fire Department’s first fire involving pool chemicals. In 1988, a warehouse containing pool chemicals in the neighboring city of Glendale caught fire, and the resulting conflagration required a major suppression effort.

Fire departments in other ares of the country have also had to deal with fires involving pool chemicals in big-box stores. In 1995, a fire broke out in a Home Depot in Quincy, Massachusetts, when pool chemicals came into contact with petroleum products. In 1996, a fire occurred at a home improvement store in Albany, Georgia, also in the area where pool chemicals were stored.

Same chemicals, different towns

The Quincy fire started at 8:23 p.m. on May 23, 1995 when the building was occupied by 60 employees and 100 customers.

The single-story building, which was of noncombustible construction, covered 122,395 square feet (11,371 square meters) and was equipped with a fire alarm and sprinkler system. The display merchandise and bulk products were stored throughout the building on a metal double-rack system.

The Quincy Fire Department and the Massachusetts State Fire Marshal’s Office determined that the fire, which started in the lower storage rack in an area in which pool chemicals were stored, was probably the result of a chemical reaction involving the pool chemicals and motor oil leaking from boxes containing lawn mowers.

NFPA’s investigation and analysis of this fire revealed several factors that contributed to the loss of property. Incompatible materials were stored too close to the oxidizing pool chemicals. Products on the racks were piled higher than the allowable storage heights and within 18 inches (46 centimeters) of the sprinklers. The sprinkler design was inadequate to protect encapsulated materials, and there were no in-rack sprinklers. Rack shelving of solid materials and wooden slats were too close together. And products were stored in the aisles, reducing clearance between products on adjacent racks.

The store’s sprinkler system and the fire department confined the fire to a small area. However, many products in the store were smoke-damaged and had to be replaced. The building’s fire alarm system was also replaced because of the potentially corrosive action of the smoke.

The 1996 Albany incident had a dramatically different outcome than the Quincy incident. Fire personnel reported structural failure within minutes of arrival, even though the building was sprinklered,  and the building was destroyed.

The fire began around 11:21 a.m. on April 16, 1996 in a fully sprinklered Lowe’s and destroyed the building and its contents, resulting in an estimated loss of $9 million. Arriving firefighters found the fire beginning to vent through the roof

and through an area where the walls had begun to separate. Despite their efforts, the fire grew rapidly, spreading through the entire building.

The store sold home improvement products, including lumber, plumbing and electrical supplies, tools, garden supplies, and pool chemicals.

The three-year-old, single-story, noncombustible building, which covered 85,000 square feet (7,900 square meters), was protected by three wet-pipe sprinkler systems. A dry-pipe system protected the garden center. Portable dry chemical fire extinguishers, manual fire alarm boxes, and a fire alarm system were also installed, and staff members had been trained to respond to fire.

Although fire department investigators couldn’t determine the cause, they established that the fire began near a rack containing pool chemicals and spread through the entire rack. The fire produced large amounts of irritating smoke, causing conditions to deteriorate rapidly.

About 100 employees and 85 customers in the store at the time of the fire were evacuated before firefighters arrived.

The fire quickly overwhelmed the building’s sprinkler systems, and fire conditions prevented firefighters from performing interior attacks. As a result, the blaze spread from one end of the building to the other, causing the roof to collapse. The building’s contents were consumed.

NFPA’s investigation revealed deviations from NFPA code requirements that contributed to the severity of the fire and to the loss of property. The oxidizers had been stored on racks that were higher and deeper than the limits imposed on retail storage. There were no solid, noncombustible vertical barriers between the oxidizers and incompatible materials, and the oxidizer storage area had no in-rack sprinklers. In addition, the store’s sprinkler systems discharge densities and areas of operation were below NFPA code requirements for oxidizer storage.

Given their recent track record, oxidizers in the form of pool chemicals are an obvious cause for concern. It’s important that they be stored properly, segregated from incompatible substances, and properly protected. It’s also important that fire service personnel responding to a fire in an occupancy containing these products be prepared to take aggressive action to contain or control the fire

Sidebar

4424 South 38th Place, Phoenix, AZ

August 2, 2000

4:58 p.m. Alarm received

5:01 p.m. Command established; report of heavy fire showing

5:02 p.m. Command orders a defensive operation; Engine 23 on the scene

5:02 p.m. Several explosions reported

5:03 p.m. Second alarm called

5:04 p.m. Deck gun and large handlines in operation

5:05 p.m. Engine 272 ordered to set up at the northeast corner of the building and use the Telesquirt

5:07 p.m. Police department reports that one building contains cyanide

5:11 p.m. Third alarm called

5:14 p.m. Structural collapse on west side with explosions; additional collapse at the southwest corner of the building

5:17 p.m. Several more explosions reported

5:18 p.m. Personnel pulled back from east sector

5:18 p.m. Safety sector reports that the building is intact, but leaning on the west side

5:23 p.m. Fourth alarm called

5:25 p.m. Wall on west side collapses

5:29 p.m. Personnel ordered to don SCBAs

6:10 p.m. Engine 23 personnel transported to hospital

6:18 p.m. Police helicopter begins aerial reconnaissance

6:21 p.m. Responsible party for the fire building is on the scene

6:44 p.m. Fire is reported moving north through the building

7:26 p.m. Fire is reported showing in the other half of the building

7:43 p.m. Foam 3 from airport is on the scene

August 3

9:04 p.m. Incident closed

Ed Comeau is the principal writer for writer-tech.com, a technical writing firm.  He was previously the chief fire investigator for NFPA, and a fire protection engineer for the Phoenix Fire Department.  Robert Duval is NFPA’s senior fire investigator.