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4th June, 2013

Excavations And The 1.2m Rule

An article caught my attention over the weekend and reminded me of a conversation I had recently had on site with a builder.

The article was a local news report about a man stuck in a 3 foot trench. Even with the help of paramedics they could not get the man or his injured foot out of the trench and had to call for additional help from firefighters.

3 feet is less than 1m.

This is a reminder that excavations of any depth can be hazardous should they collapse, and that excavations of any depth are at risk of collapse if they are unsupported.

During a recent conversation on site I was told by a builder that they would not be installing trench supports as the excavation in question would be less than 1.2m deep.

Given that the builder was not a competent ground worker and would be subcontracting out this work, I advised him that a competent person would need to assess the ground conditions and the trench to determine what support would be required before access could be made.

1.2m is no longer the threshold for the need to support an excavation. The need to support an excavation very much depends on ground conditions and other risk factors.

The 1.2m rule for trenches used to be in older health and safety regulations and is often still quoted today.

The basis of the rule is that, if a trench is under 1.2m deep, then people can enter the trench without the sides of the excavation being supported or battered back.

However, this 1.2 rule is not in any of the current regulations.

Looking at the article regarding the 3 foot trench it is easy to see why.

For some activities and materials [or] ground conditions, danger might arise from excavations less than 1.2m deep and in other exceptional circumstances excavations exceeding such a depth may not present potential danger. Specific works should be assessed by someone who is competent to assess the risk and determine what controls are needed.

HSE, New guidelines on deadly excavations, NCE (2011)

Often, workers within trenches may be kneeling down to carry out work, laying blocks, installing pipes or cables.

If the sides cave in at 1.2m, workers on their knees could easily be buried. Even with other operatives on site, it could take an hour to carefully dig a buried person out.

Current health and safety regulations tend to not generalise. What is safe and perfectly acceptable on one site, may be dangerous on another.

Excavations at 1m may be safe to enter without support on one site, but on another, it may be at high risk of collapse. The ground conditions, the weather conditions, and the surrounding work activities need to be taken into consideration.

Remember, every construction site is different, and every excavation is different. Never enter an excavation without checking it is safe.

Control excavation activities on your sites with our excavation permit to work, giving you a checklist of controls and a record of the steps taken.

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