A number of incidents have occurred where employees have been seriously injured after being engulfed while working in trenches that have collapsed.
Wet weather and increased ground moisture has created a higher risk of ground slippage and engulfment.
Trenches greater than a metre deep can pose a significant risk to workers, especially those who are bending down to work on pipes or other services. The risk of fatalities will also considerably increase with depth.
Before trenching work starts, ensure:
- work is planned so it can be done safely, including determining appropriate engulfment protection and site security requirements
- a safe work method statement (SWMS) is developed for high risk work that involves mobile plant or if the trench depth is 1.5m or more
- an emergency response plan (ERP) is developed to deal with potential incidents (eg worker rescue, ground slip or flood).
When undertaking trenching work, ensure:
- a competent person, experienced in trenching works, supervises and monitors the work
- workers are instructed on the ERP and SWMS (and it is followed)
- workers never work ahead of the protection or remove it prematurely if protection is being progressively installed
- materials, spoil and plant are kept away from the edge of the trench
- workers not involved with the work and the public can’t access the trench and works area
- where there is a risk of members of the public accessing the works area, secure and stable site fencing is provided to prevent access
- ensure, while the trench remains open, the trench and site security is inspected regularly - and as soon as possible - after any event that could affect the safety of the trench (eg a storm or ground slip).
Engulfment protection methods
Workers must be protected while undertaking any work where they are required to enter a trench and there is a risk of engulfment. When appropriately used, the following methods can provide the required protection:
- batter the walls to a safe angle.
- bench the walls to form one or a series of steps.
- shore up the walls to support the sides.
- work inside trench shields.
Trench shields do not support the ground - they provide protection to workers within the shield, therefore workers must stay within the confines of the shield at all times.
A safe method to enter and exit the trench or shield must also be provided (eg a sufficiently long, secured ladder and landing platform).
An ERP must be developed and employees instructed in emergency procedures to ensure a prompt and safe emergency response should an imminent risk of, or engulfment occurs.