Workers Burnt in Sewage Chamber Explosion - WSH Bulletin

Incident

On 21 October 2009, six workers were tasked to seal two sewer pipes inside an unused sewage chamber at the junction of Macpherson Road and Aljunied Road by filling the two pipes up with a cement compound. When they were preparing the worksite for this work, an explosion followed by a fire occurred in the sewage chamber. All six workers were injured. Preliminary findings revealed the presence of flammable gases in the sewage chamber. Investigation is ongoing to determine the cause of the explosion, the source of the gases and the possible source of ignition.
Recommendations*
1. Conduct Risk Assessment: Adequate risk assessments must be conducted before starting any work. Through risk assessment, all potential hazards can be identified and appropriate actions taken to eliminate these hazards or reduce the risks involved. One possible hazard in this incident was the presence of a hazardous atmosphere in the sewage chamber.

2. Entry Permit and Permit-To-Work: The supervisor of the person who is to enter or work in the confined space must apply for an entry permit. The entry permit must be approved by the authorised manager, and should be validated on a daily basis if work in the confined space needs to be continued. Additionally, a Permit-to-Work system must be put in place implemented to ensure that hazardous works such as hot works are properly assessed for safe execution.

3. Continuous Monitoring of Atmosphere: A competent person such as the confined space safety assessor must test the atmosphere of a confined space for oxygen, flammable and toxic gases or vapour, and certify that the space is safe for entry before work commences. The atmosphere needs to be monitored constantly to ensure it remains within the safe limits to carry out the work. Among other criteria, the confined space should only be certified safe for entry if:
• The oxygen level is within 19.5% to 23.5% by volume.• The level of flammable gas is less than 10% of its Lower Explosive Limit (LEL).• The level of toxic substances is less than the Permissible Exposure Levels (PEL).

4. Provide Adequate Ventilation: Suitable and adequate ventilation should be provided at all times. It is important to provide fresh air and/or to dilute and remove any contaminants to a safe level. A combination of forced or supplied and exhaust ventilation can be used to ensure adequate ventilation of the space.

5. Emergency Response Plan: For work involving confined spaces, an emergency response plan (ERP), including rescue equipment, has to be put in place. Among other requirements, the plan should include the following:
• Ensure line of communications is available at all times during the work.• Ensure quick means of escape that are suitable for use by every person who enters the confined space.• Make retrieval devices and “breathing apparatus” (BA) sets readily available for use in case of an emergency. • Remind workers that they must follow the ERP and not rush in to rescue co-workers as by doing so, they might endanger their own lives.• Train supervisors, workers and other personnel on the actions to be taken during an emergency.

Further Information

1. Workplace Safety and Health Act 2006, please click here.
2. Workplace Safety and Health (General Provisions) Regulations 2006, please click here.
3. Workplace Safety and Health (Risk Management) Regulations 2006.
4. Workplace Safety and Health (Confined Spaces) Regulations 2009, please click here.
5. Risk Assessment Guidelines.
6. Approved Code of Practice for Entry into and Safe Working in Confined Spaces [CP 84 : 2000]
7. Technical Advisory for Confined Spaces, please click here.

* Please note that the information provided is intended to enhance workplace safety and health so that a similar recurrence may be prevented, and is not exhaustive. The information provided should not to be construed as implying any liability to any party nor should it be taken to encapsulate all the responsibilities and obligations of the reader of WSH Alert under the law.