Tuesday, March 9, 2010

WSH Alert – 2 Workers Killed in a Chemical Explosion - WSH Bulletin

8 Mar 2010

Incident

On 23 Jan 2010, an explosion caused the roof of an atmospheric Diethylene Glycol (DEG) storage tank to be blown off. Two workers who were installing nitrogen pipelines on the tank roof at the time of the accident were killed. Investigation is still in progress.

Figure 1: The DEG storage tank, which is about 6m in diameter and 20m high.

Figure 2: Roof of the tank that was blown off and landed on a field outside the premises.

Recommendations

1. Conduct risk assessment: Prior to the start of work, a risk assessment should be carried out to determine the potential hazards and risks that might arise during the installation or replacement of a piping system. DEG has a flash point of 138 ºC (closed cup) and 143 ºC (open cup). Control measures and safe work procedures must be established to mitigate the risks, and be communicated and implemented to ensure the safety and health of the workers involved. Some of the hazards relevant to this incident include:

a) Excessive built-up of pressure in storage tank due to faulty breather valves
b) Hazards associated with hot work
c) Falls from height while working on top of the tank

2. Ensure proper supervision: It is important to ensure that any pipe replacement works are carried out under the close supervision of a competent person with adequate knowledge of the storage system, properties of the substances used and their associated dangers.

3. Establish safe work procedures: Safe work procedures must be appropriately documented to enable workers to identify the valves correctly, and to assist them on the proper steps to operate the different valves safely such that valves will not be opened or closed erroneously.

4. Inspect vessels / pipes regularly: Under the Workplace Safety and Health (General Provisions) Regulations, it is the duty of the owner of a pressure vessel or pipes that contain or convey hazardous substances to ensure that they are properly inspected before use. Thus it is important to inspect the valves, piping systems and storage tanks regularly to ensure that they are in good condition. Faulty valves must be reported to the supervisor who will assess if it is safe to continue with the work.

5. Check storage pressure: Workers are allowed to work on top of a storage tank only if the pressure inside the tank is known and it is safe for them to do so. Appropriate pressure gauges should be installed at strategic locations to indicate the pressure within. Whenever practicable, pressurised tanks should be purged to safe atmospheric pressure level before works are carried out at the top of the tank.

Further Information

1. Singapore Standard SS 532: 2007 Code of Practice for the Storage of Flammable Liquids
2. Singapore Standard SS 586 – 3 : 2008 - Specification for hazard communication for hazardous chemicals and dangerous goods - Preparation of safety data sheets (SDS)
3. Workplace Safety and Health (General Provisions) Regulations
4. Ministry of Manpower’s Risk Assessment Guidelines. Click HERE.
5. Ministry of Manpower’s guidelines on Prevention and Control of Chemical Hazards. Click HERE.
6. WSH Council’s Technical Advisory for Flammable Hazardous Substances. Click HERE.

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