Accident Advisory: Mishaps at excavation worksite

Ref No.: 301018 (1)
UEN: S97SS0046G

Dear Valued ASPRI Members,

Accident Advisory: Mishaps at excavation worksite

On 12 September 2018 around 11.50am, a worker was standing at the edge of a trench  assisting an excavator operator to monitor the depth of the excavation. Subsequently, the worker fell into the trench when the soil he was standing on collapsed. As a result, he was buried under the soil. The worker was extricated and conveyed to the hospital where he passed away.

Recommendations
Persons in control of similar workplaces and work activities such as occupiers, principals and employers are advised to consider the following risk control measures to prevent similar recurrence:

Statutory Requirements for Excavation Work
• A Permit-To-Work (PTW) must be implemented for excavation work in a tunnel or
hole in the ground exceeding 1.5 metres in depth. A sample PTW application form
can be found in Annex A of SS 562: 2010 Code of Practice for Safety in Trenches,
Pits and Other Excavated Areas.
• An excavation deeper than 1.5 metres must be fitted with adequate shoring
by underpinning, sheet piling, bracing or other means of shoring to prevent
collapse. Such shoring must be designed before commencing
any excavation work. Examples of shoring systems for excavations and trenches
can be found in Annex D of SS 562.
• Generally, an excavation that is less than 1.5 metres deep, may not require any
shoring support if the ground is self-supporting. However, shoring support must
be supported in the following scenarios:
– When there are external loads applied, or
– When the stability of the excavated sides is likely to be affected by weak ground or high underwater, especially in inclement weather.

Such hazards must be identified in the risk assessment before work commencement.

  • PTW holders should familiarise themselves with the relevant regulations,
    standards, codes of practice and guidelines before opening up a trench. The
    contractor carrying out the works is required to comply with the conditions of
    the permit to ensure safety of the workers and public during excavation works.
    • The occupier should carry out the necessary site inspection and provide supervision
    to ensure compliance to the conditions specified in the PTW.

Temporary Edge Protection

  • Install guard-rails to prevent workers from falling into the excavation if it exceeds
    2 metres in depth.

Safe Access/Egress

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

Emergency Response Plan

  • Establish an emergency response plan to dictate the course of action to take in
    the event of risk of injury or death. Such emergencies include flooding, gas
    leakage, discovery of ordnance, fire and explosion.

General Safety Tips for Excavation Works

  • Keep heavy equipment, excavated soil and other materials at least 1 metre from the edge of the trench/excavation.
  • Identify other sources that might affect trench stability.
  • Identify where underground utilities are located before digging.
  • Test for atmospheric hazards such as low oxygen, hazardous fumes and toxic gases.
  • Never work under a suspended load.
  • Inspect trenches following a rainstorm or other water intrusion.
  • Inspect trenches after any occurrence that could have changed the conditions in the trench.
  • Ensure that workers are equipped with and wearing high visibility clothing when exposed to vehicular traffic.

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 accident. Such hazards include:

• Improper shoring (which can lead to collapse of excavation).
• Instability of excavation and adjoining structures.
• Accumulation of water.
• Contact with utilities.
• Inclement weather.
• Contaminated ground.
• Underground obstructions.

A comprehensive list of all foreseeable 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 RA should look into the following areas, but not limited to:

• Fall of workers into the excavation.
• Fall of materials into the excavation which may engulf persons within.
• Movement and position of heavy equipment.
• Placement of excavated materials.

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 (Work at Heights) Regulations
6. SS 562: 2010 Code of Practice for Safety in Trenches, Pits and other Excavated areas
7. SS EN 1997-1: 2010 (2018) + A1:2018 Eurocode 7: Geotechnical Design – Part 1: General Rules
8. SS EN 1997-2: 2010 (2015) Eurocode 7: Geotechnical Design – Ground Investigation and Testing
9. Building Control (Amendment) Act 2012 and Regulations 2012: ERSS – Submission Requirements
10. WSH Guidelines Anchorage, Lifelines and Temporary Edge Protection Systems
11. US Occupational Safety and Health Administration’s Trenching and Excavation Safety OSHA 2226-10R 2015
12. WorkSafe New Zealand’s Good Practice Guidelines for Excavation Safety

* Information on the accident is based on preliminary investigations by the Ministry of Manpower as at 20 October 2018. This may be subject to change as investigations are still on-going. Please also note that the recommendations provided here are not exhaustive and they are meant to enhance workplace safety and health so that a recurrence may be prevented. The information and recommendations provided are not to be construed as implying any liability to any party nor should it be taken to encapsulate all the responsibilities and obligations under the law.