Accident Advisory: Worker succumbed during excavation works

Ref No.: 121218 (1)
UEN: S97SS0046G

Dear Valued ASPRI Members,

Accident Advisory: Worker succumbed during excavation works

11 December 2018, Ref: 1819061

On 20 October 2018 around 11.15am, two workers were working in an excavated trench. They were assisting with the installation of timber shoring, when one of the trench walls collapsed, trapping both workers with soil up to their waists. Both workers were extricated and sent to the hospital, where one of them subsequently passed away. The other worker was treated for minor injuries at the hospital.


Figure 1: Overview of the accident scene.

Recommendations

All excavation work is potentially hazardous. Contractors and key stakeholders are reminded to comply with all relevant statutory requirements stipulated in the regulations administered by regulatory authorities including that of the Ministry of Manpower and the Building & Construction Authority.

As a minimum requirement, all contractors carrying out trenching or excavation work are advised to follow the requirements prescribed in the Approved Code of Practice SS 562 (SS 562) for trenches, pits and other excavated areas. Failure to do so may result in an accident and incur punitive action if an investigation reveals serious lapses under the Workplace Safety and Health Act.

Persons in control of similar workplaces and work activities such as occupiers, principals and employers are advised to adhere to the following risk control measures in the SS 562 (Note: You are advised to refer to the SS 562 for all requirements pertaining to trenching and excavation works.):

Permit-to-Work
• A Permit-To-Work (PTW) system must be implemented for excavation work exceeding 1.5 metres in depth.
• PTW stakeholders (i.e. Applicant, Safety Assessor, Project Manager) shall familiarise themselves with the relevant regulations, standards, codes of practice and guidelines before excavating the ground.
• The applicant for a PTW should be a Competent Person appointed in writing, with appropriate experience and knowledge of similar excavation work for the application of different types of soil protection system suitable to the specific site conditions.

Selection of an effective Soil Protective System
• If an excavation operation is being carried out and has progressed to more than 1.5 metres in depth, information on the soil type and conditions must be made available to the contractor by the developer to facilitate proper planning to
continue with the safe execution of the excavation.
• Excavations of 1.5 metres or less in depth shall be examined by a Competent Person to determine if shoring system or other means of protective system is required.
• Excavation exceeding 1.5 metres shall be protected by shoring or other means of protective system. It has to be designed by a Professional Engineer (PE) and be constructed in accordance to the PE’s design drawings.
• The Competent Person should prepare the Method Statement (MS) for the excavation (covering all stages of work, from start to backfill, including the construction of soil protective system) to minimise the hazards identified. The MS is to be reviewed and endorsed by the PE if excavation is above 1.5 metres in depth or as determined by the Competent Person.

Site management and supervision
• Work on-site should be supervised by the same Competent Person appointed above. He must have the authority to make decisions necessary to ensure the safety of the workers, the excavated area and its surroundings.
• Ensure all site personnel, including workers, deployed to work in excavation works have prior experience in excavation. In addition, they should be briefed via tool box meetings on the possible hazards and corresponding control measures regarding excavation works.
• No site personnel/equipment should be allowed to go near (less than 1 metre) an excavation side or into the excavation that is not protected by shoring or other protective system without the approval of the Competent Person.
• The sides of the excavation should be sloping or be battered back to a safe angle of repose or be supported by suitable shoring or other suitable means to prevent a collapse.
• The excavation/trench protective support system must be followed strictly to the approved MS and the design approved for the excavation. In general, never work ahead of the side supports, even when erecting shoring. A trench box should be used whenever necessary to protect workers who are working in the un-shored part of the excavation.
• The excavation or trench support must be installed without delay as the excavation progresses, and the strutting completed before the ground relaxes significantly.
• The materials for shoring or other protective system should be as specified and approved by the Competent Person in accordance to the design and
drawings. Generally, the materials should be sound and of integrity.
• The supervisor at site should be aware of the assumptions made in the design of the support and should carefully monitor the actual situation on site. Any changes from the assumed conditions should be reviewed and referred to the Competent Person for consideration, comment and revision.
• Inspect the excavation after any occurrence that could have changed its conditions, e.g. after inclement weather.
• After completing works inside the excavation, the shoring, if any, should be removed properly. Shoring shall not be removed until an assessment has been carried out by the Competent Person to ensure the safety of workers and other persons on site, especially during and after inclement weather. It should be dismantled only by competent workers operating under supervision. The persons should always be on top of the excavation whenever practicable.

Regular inspection
• For the safety of work proceedings, excavations shall be examined prior to entry and at regular intervals to ensure that the excavation and its supporting systems are stable and intact. The risk assessment should determine the intervals of inspections, and the inspections should be conducted and documented by a Competent Person.
• The soil condition and the state of shoring, battering and trench walls should be frequently checked by the Competent Person for signs of the earth fretting, slipping, slumping or ground swelling.
• Where necessary, repair the excavation or strengthen the shoring system (in accordance to the methodology prescribed by the designer) before allowing work below ground to continue.

Safe access/egress
• Ensure that safe means of access to and egress from the excavation is provided to workers who are required to work in the excavation.

Risk Assessment

Possible hazards during excavation works should be identified prior to work commencement, and mitigating measures must be implemented to eliminate or reduce the risk of accidents. Such hazards include:

• Instability of excavation and adjoining structures.
• Accumulation of water.
• Underground obstructions.

A list of possible hazards in excavation work is given in Clause 4 of SS 562.

Conduct a thorough site-specific Risk Assessment (RA) for all work activities to manage any foreseeable risk that may arise during excavation and trenching. The areas that the RA should take into account include, but is not limited to, the following:

• Workers falling into the excavation site.
• Materials falling into the excavation site which may endanger persons within.
• Collapse of excavation site.

Further Information

1. Workplace Safety and Health Act
2. Workplace Safety and Health (Risk Management) Regulations
3. Workplace Safety and Health (General Provisions) Regulations
4. Workplace Safety and Health (Construction) Regulations
5. Workplace Safety and Health (Design for Safety) Regulations
6. Building Control (Amendment) Act 2012 and Regulations 2012: ERSS – Submission Requirements
7. SS 562: 2010 Code of Practice for Safety in Trenches, Pits and other Excavated Areas
8. SS EN 1997-1: 2010 (2018) + A1:2018 Eurocode 7: Geotechnical Design – Part 1: General Rules
9. SS EN 1997-2: 2010 (2015) Eurocode 7: Geotechnical Design – Ground Investigation and Testing
10. WSH Guidelines on Design for Safety
11. WSH Alert Accident Advisory – Worker Dies at Excavation Worksite (29 Oct 2018, Ref: 1819055)