Accident 2
Fire and toxic release at an electronics production plant
Sequence of events
At 20:22 on 26 April 1998 an operator of the plant saw white fumes in correspondence with the CDI unit, adjacent to the hydrogen compression room and to the refrigeration units. The operator alerted the foreman, then the shutdown operation of the plant, controlled by a microprocessor with display on the control-panel, was activated. At the same time nearby voluntary fire brigades arrived, having been alerted by a person passing by who had seen the smoke. When the personnel identified the source of the smoke as a release of hydrochloric acid (HCl) from the combination of silicon tetrachloride (SiCl4) with water (H2O) (due to the presence of humidity in the air and in the soil), they proceeded in establishing a vertical water curtain, in compliance with the emergency plan, in order to avoid the displacement of the fumes due to the wind, attempting at the same time to avoid direct contact of the water with the SiCl4. The external firefighting teams attempted to abate the fumes without similar care, causing the intensification of the chemical reaction described above.
An HCl cloud formed and was transported by wind to a residential area in the vicinity of the establishment at a few kilometres distance, principally to the south and also affecting a major road. The fire fighting water also abetted infiltration of chlorine and silicone in approximately 400m2 of soil around the plant. No one was injured.
Important findings
The plant was a relatively small site and an accident of such potential severity apparently had not been considered for risk management. It may be that such a large release of HCl due to water interacting with SiCl4 had not been imagined.
Although the involvement of external fire fighters was foreseen in the emergency plan, it appears that many local fire fighting forces, particularly volunteer operations, had not been consulted.
Accident 3
Fire at a chemical production plant
Sequence of events
At 14:20 on 21 July 1992 a series of explosions leading to an intense fire broke out in a storeroom in the raw materials warehouse. Due to overheating, azodi-isobutyronitrile (AZDN) was released into a store reserved for oxidising materials. Due to its incompatibility with the AZDN dust released, Ammonium Persulphate (APS), which was also in the store, they ignited. The fire spread rapidly to the remainder of the warehouse and external chemical drum storage. The fire service was called at 14:22 and the first appliance arrived from the local station only a short distance away by 14:28. Thick black smoke and flames were escaping from the roof in the vicinity of the storeroom and the quantity of smoke rapidly developed as the fire gained a swift hold, spreading to the external drum storage. A 25 km/hr wind was blowing at ground level from slightly north of west (280°) causing the black cloud of smoke to drift eastwards, affecting the traffic flows on two main roads over two miles away. Eventually the smoke could be seen from the nearby city centre, some 16 km away. The site emergency plan was activated and employees were effectively evacuated.
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Considerable difficulties were experienced in obtaining an adequate water supply as the water mains in the area were incapable of supplying the fire-fighting needs of a large fire. Foam was also used at the fire, including all of the stocks held by the company. It was applied to parts of the fire to prevent or slow its spread from the warehouse to drums stored externally. However, foam was unsuitable for cooling the finished goods warehouse and drums of flammable liquids held in the fire block storage area. These operations consumed substantial quantities of water.
At 14: 55 the siren sounded to warn the public and employees to warn of a major accident and the possibility of toxic fumes. The siren continued to operate until 15:40 when power to the whole site was cut off by the electricity board because the fire was threatening the main sub-station. The loss of power also caused a shutdown of the company's effluent pumps and the escape of contaminated fire water from the site boundaries.
None of the company employees were injured. 33 people, including three residents and 30 fire and police officers were taken to hospital where they were primarily treated for smoke inhalation. Six people were detained. Approximately 2000 local residents were confined to their houses and residents in eight properties immediately adjacent to the raw materials warehouse were evacuated. Firewater run-off caused significant river pollution. The total cost of company property damage was estimated at £4.25 million and substantial indirect costs were incurred.
The fire was finally contained at about 1740 h. Power was restored to the site at 20:45.
Figure 3: Plastic drums on the fire block flammable liquid storage area showing heat radiation damage and effects of pressurisation. (HSE, 1992)
Important findings
The crucial error leading to the fire was the incorrect categorisation of AZDN and its consequent storage with oxidising agents with which it was chemically incompatible.
The company had been aware that water mains were not adequate for certain scenarios. There had been discussions with the fire service but a suitable alternative had not been provided.
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The serious potential for escalation of the incident was evidenced by numerous plastic drums on the fire block which were damaged by radiant heat. The fire service made a considerable effort to cool these containers of flammable liquids during the course of the fire and successfully prevented their ignition.
The police helped to enforce the shelter-in-place and a limited evacuation.
Fire officers had made early contact with the company's incident controller and had strongly advised the sounding of the emergency siren provided by the company to warn the public and employees in the event of a major accident. This advice was initially not acted upon.
eMARS – Accident 21/07/1992
http://www.hse.gov.uk/comah/sragtech/casealliedcol92.htm
Accident 4
Toxic release at a chemical production plant
Sequence of events
In a sulphur dichloride (SCl2) distillation facility in a chemical plant, a spillage of SCl2 occurred in the retention area for a distillation column in the final stages of distillation, after a leak from a recirculating pump. The SCl2 hydrolysed upon contact with ambient humidity, causing an intensive emission of hydrogen chloride (HCl), which was not detected by the HCl gas detector of the column. But a safety detector installed in the unit gives the alarm at 13:12. The controller placed the unit in safety shut down and then triggered locally the audible and visual alarm while alarm messages appear on the control screens in the control room. The internal emergency plan was activated and the 35 employees were evacuated. The internal fire team, supported by 40 external firefighters, equipped themselves with breathing apparatus and plugged the leak. The cloud of HCl was overcome using 4 lateral fire hose lines. The 120 m³ of water used is collected in a retention pond for reuse in production. The internal emergency plan is terminated at 16:15 pm. The next day a specialized company pumped 800 liters (1,200 kg) of sulfur dichloride from the retention basin into a storage tank. The HCl release remained confined inside the building. A similar accident occurred on the site in 2006 (ARIA 31691).
Important findings
It was discovered that a similar accident had already taken place at the site in 2006, resulting from the failure of a pressure sensor. [ARIA 31691] In this case, the release was also contained by a rapid emergency response.
(eMARS 15/04/2013 and ARIA No. 43681)
Accident 5
Lightning strike causes explosion at a distillery
Case 2
In a distillery, a 5,000-m³ tank containing 1,000 m³ of ethanol at 96% concentration exploded when lightning struck and then ignited. The raised roof fell into the reservoir, which remained intact. However, the tank foot valve cracked upon impact.
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An emulsifier delivered 2 hours later enabled preventing the fire from spreading to the 1,000-m² retention basin. The blaze was extinguished in 3 hours and the fire-fighters for over 5 hours cooled 3 adjacent 2,500 m³-tanks exposed to the intense heat.
During the emergency response, 23,000 litres of emulsifiers stored onsite and a total of 7,000 m³ of water (including cooling water) were used. The loss was valued at 30 million francs (including 2.5 million of alcohol destroyed and 3 million of emulsifier). The extinction water (1,500 m³) collected in the retention basins would be diluted in a lagoon. An outside organization was called to verify the electrical installations of the storage zone.
Important findings
An internal response plan drill conducted 2 months earlier, based on a comparable scenario involving one of the tanks involved in the accident, served to facilitate the actual intervention. It had been recommended to install flame arrestors on the vents and the breathing valves on the tanks following a lightning risk evaluation study conducted 18 months prior to the event.
(eMARS#394 and ARIA No. 18325)
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Lessons learned
The case studies described here are illustrative of the importance of several aspects of emergency planning and response. In particular, following points should be taken into account in planning and preparedness:
- Identifying and planning on realistic scenarios is the starting point.
- Reviewing past accidents is important for identifying possible scenarios but also as input to response needs.
- Small sites that meet Seveso (high hazard) criteria are capable of serious accidents. They need to know their high risk scenarios and have an emergency response plan.
- Training and co-ordination with other responders can have an enormous impact on the effectiveness of response. Responders can put themselves and others at risk if they don’t know what they’re doing. Failure to involve relevant external responders in training can have serious consequences. Don’t overlook this aspect.
In Case 2, the responders created a significantly greater toxic release because they were not sufficiently trained.
- Emergency equipment and materials form the backbone of response operations. Critical needs should be identified with back-up options immediately available.
- The response effort relies heavily on good communication between all parties and with the public. Technology needs to be tested regularly and back-up systems should be in place in case key elements (sirens, wireless networks, etc.) become disabled.
- Emergencies often require decisions to be made quickly and timing is everything. Decisions that may be needed should already be anticipated in the planning and assigned a clear decision-making process (who makes decisions, what information is needed) with well-defined criteria that recognises criticality of timing and how to deal with uncertainty.
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