|
Case 3 – Fire at a refilling and distribution centre for liquefied and compressed gas cylinders
Sequence of events During a period of extreme heatwaves, consisting of bright sunlight and ambient temperatures exceeding 36°C, several explosions followed by fire took place at a bottling plant. The facility fills and distributes liquefied and compressed gas cylinders, rents welding machinery, and sells welding supplies. During normal operations, it has about 30,000 compressed gas cylinders containing oxygen, nitrogen, propane, propylene, acetylene, carbon dioxide, helium, and other speciality gases onsite, employing around 70 people. A technician retrieving cylinders from an outside storage area saw a three-meter-high flame coming from a cylinder and activated the fire alarm. As workers and customers evacuated, the fire spread to adjacent cylinders. After 4 minutes, the fire covered most of the facility’s flammable gas cylinder area and chain explosions took place.
With explosions propelling cylinders in all directions inside and outside the facility, firefighters set up a perimeter, evacuated local residents, directed a water stream on the fire, and extinguished secondary fires started by burning cylinders and projectiles landing offsite. The fire was finally controlled following a 5-hour intervention. Damages included a burned-out empty commercial building, burned cars, a one-meter hole in the wall of one residential building, broken windows, and other destruction to residential and commercial buildings. Cylinder parts travelled as far as 250 meters from the area of the explosions. The fire plume spread asbestos from ruptured acetylene cylinders approximately over a 1,5km wide area, while one resident experienced a severe asthma attack and died. The facility was extensively damaged by the fire and the extinguishing water while about 8,000 cylinders were also destroyed.
Important findings Direct sunlight, as well as radiant heat from the asphalt, heated the propylene cylinders, while high ambient temperatures limited any natural air-cooling. Moreover, the returned cylinders, where the fire started, contained less gas than full cylinders, started heating up at an elevated rate. As the cylinder wall temperature rose, the internal pressure increased, causing the relief valve to open and vent propylene. Probably due to an electric spark or discharge, the released propylene was ignited.
- Temperature of the nearby cylinders rose, as the heat from the fire was supplementary to the heatwave, releasing more propylene into the fire. As a result, the liquefied petroleum gas (LPG) area of the facility became fully involved in the fire.
- Barriers to limit the spread of fire and explosion, deluge systems or fixed fire nozzles to cool cylinders in case of a fire as well as gas and fire detection systems that can activate alarms and fire mitigation systems were lacking.
Lessons Learned Implementation of required storage protocols for hazardous materials. A critical principle of safe storage of hazardous goods is the strict adherence to safety protocols associated with the substance in question. In this particular case, the substance consisted of propylene and propane cylinders. Standard practices for storing cylinders are well-known and include maintaining recommended safety distance between cylinders, organising full and empty cylinders in separate locations, separating storage compartments for cylinders from any potential heat sources, and distancing them from flammable and combustible liquids that could easily ignite.
Packaging and storage standards for different types of hazardous substances typically address a number of elements, including the type of container and its composition, the degree of isolation or distance to be respected from other types of materials, temperature conditions, bonding and grounding of static electricity, and other parameters. For example, flammable substances should generally be stored only in dry, well-ventilated areas that are not exposed to heat or direct rays of the sun, or lightning. Special attention may be required for specific substances, such as ammonium nitrate, whose unique properties require particular handling and storage conditions. Measures should also include any controls necessary to combat climate and weather extremes of the location, for instance, potential excess humidity in port locations.
Handling and storage guidelines for dangerous substances with all hazardous properties, e.g., flammability limits, water reactivity, etc and optimal storage conditions (i.e., temperature and humidity) are available through the SDS which should be consulted before substances are sent to storage. If the correct storage conditions cannot be met for particular dangerous substances, then they should not be permitted in the warehouse.
Detection mechanisms and mitigation systems. Warehouses should adhere to recommended practices for detecting liquid and gas releases, changes in temperature, or other warning signs specific to the range of substances stored in the warehouse. Detection systems are often coupled with automated safety systems that are programmed to trigger alarms and mitigation measures (e.g., deluge systems) when parameters are exceeded. For example, for gas cylinders, detection of flammable gases should be in place to dissipate the gas before ignition, reducing the likelihood of uncontrolled fires. Fixed fire protection such as fire monitors, deluge, or sprinkler systems can immediately cool cylinders reducing the likelihood of additional cylinder releases, fire spread, and off-site consequences.
Firefighting medium (water, foam or other agents) should be used according to the hazard classification of the substances in storage avoiding any reaction between the firefighting medium and hazardous substances. The SDS contains all relevant information on suitable firefighting mediums as well as advice for firefighters.
Internal site planning. The placement of hazardous substances and the location of storage units should also consider domino effects of potential accident scenarios involving the dangerous materials in storage. For example, burning cylinders and fragments, acting as projectiles, can strike people and property both onsite and offsite, sometimes causing significant harm. They can even cause an escalation in the accident sequence if they hit another hazardous substance container, which then may also explode or release noxious gas or fluid. In this context, warehouse operators may consider storing hazardous substances under reinforced structures to mitigate the effects of an explosion as well as assess the facility’s segregation policy.
Land use planning. Potential offsite consequences on urban areas should be thoroughly assessed, considering appropriate safety distances from residential buildings and the warehouse structural design elements that can minimise the possibility of impacts offsite. The high potential for domino effects, when mitigation measures are inadequate to control the event escalation, can represent a very high risk for offsite populations and structures. In this particular case, the projectiles from the explosion of gas cylinders reached an area of 250m from the epicentre of the main explosion. The Tianjin, China warehouse fire (2015) and the fire and explosion of a fertiliser warehouse in West, TX, USA (2013) are both examples of the excessive danger that serious warehouse fires and explosions pose to their surroundings due to expulsion of projectiles, massive overpressure, and the propagation of fire to nearby objects and structures.
Source: United States Chemical Safety and Hazard Investigation Board, Praxair Fire
|