At 14:20 on July 2l, 1992, a series of explosions rent a storeroom at a raw materials warehouse of Allied Colloids.
A fire spread rapidly to the remainder of the warehouse and external chemical drum storage. None of the company employees were injured, but 33 people, including three residents and 30 fire or police officers were taken to hospital where they were treated for smoke inhalation.
Incompatible substances stored together could lead to chemical reactions. Such reactions could result in fire, explosion or release of toxic substances.
Neglecting warehouses during planning and construction or during normal operation could result in serious process safety incidents.
Chemicals not correctly classified for storage purposes could lead to incompatible chemicals stored in close proximity to each other resulting in reactions taking place in the event of spillage or release.
The fire was preceded by the rupture of two or three containers of unstable azo diiso butyronitrile (AZDN) heated by an adjacent steam condensate pipe about 50 minutes earlier.
Rupture created a dust cloud that came into contact with sodium persulphate (SPS) and possibly other oxidising agents which were stored in the storeroom, causing delayed ignition followed by explosions and the subsequent major fire.
Disaster causes identified
Fire was initiated by AZDN kegs that thermally decomposed. Thermal decomposition started because of the proximity of the kegs to a hot steam condensate return line.
AZDN powder released reacted with sodium persulphate, an oxidising agent, which was stored adjacent to it. AZDN, a reducing agent, had been wrongly classified as an oxidising agent and stored in an ‘oxystore’.
Oxystores in the warehouse were not used for their original purpose, which was to store oxidising chemicals.
Oxidising agents were stored with reducing agents, surprisingly! Steam heat pipes and panel in Oxystore 2 were not effectively isolated from the steam supply after the primary purpose of the storeroom was changed from frost sensitive flammable products.
Hospitalisation of 33 people followed. Residents of eight adjacent houses evacuated and 2000 people were confined to their houses for several hours. River Calder was polluted as the local sewer system could not handle the fire water runoff, and 10 000 fish died.
Property damage of about £ 4.5-million resulted. Raw materials and a warehouse was destroyed. Substantial damage to the finished goods warehouse. A road tanker containing 16 tonnes of butyl acetate was burned out. The company was prosecuted and fined £100 000.
Effective emergency plans.
Summons emergency services immediately when an incident happens.
Safety performance in storage facilities to be regularly monitored
Audits are recommended.
Managers, supervisors and operators of chemical warehouses to be given appropriate training regarding to the placement and segregation of chemicals.
Safety related maintenance or engineering requests should be specially identified and given appropriate priority.
Segregation policy for chemicals must be effectively implemented.
Incompatible substances must be segregated and stored separately.
Training should be given to staff.
Non-production departments, especially warehouses should not be neglected areas so far as safety and health is concerned.
Safety policy statements should be updated immediately following changes in a management system.
Emergency services should be summoned to any incident with the potential of escalation and this provision shall be incorporated into the emergency plan.
Emergency plans should set out actions for pollution prevention from major incidents.
Some chemicals burning in air, change their state, or react to produce decomposition products. The original substance may not dominate the list of fire risks. Significant volumes of additional carbon monoxide, hydrogen cyanide, and other substances may be generated by reactions during exposure to air, heat, fire, or flooding.
These reactions have to be factored into projections of fire fisk regarding structures, plant, and packaging. Where many substances are involved, several complexities may arise, causing a chemical cocktail in the plume.
Source; SA Process Safety Forum, CAIA.
PHOTO; plan of the raw materials store in the warehouse, where the disaster started.