Excavations And The 1.2m Rule

If you only take one thing away from this blog post, let it be this - excavations can be unsafe at any depth, and there is no 1.2m excavation rule that removes the need for trench support. Read on to find out why people believe this rule, why it's a myth, and what you need to do instead.

When I first wrote this post back in 2013, a news article had caught my attention. It reminded me of a conversation I had with a builder on a project at the time.

During a conversation on site, the builder said they would not install trench supports as the excavation in question would be less than 1.2m deep.

The builder was planning to subcontract the excavation work. He wasn't a competent ground worker, and at the time of the conversation, he didn't fully know the ground conditions. But he believed that he didn't need trench supports because the excavation was less than 1.2m deep.

I advised him that a competent person would need to assess the ground conditions and the trench to determine what support would be required to make the excavation safe.

So what was the news article? The article was a local news report about a man stuck in a 3-foot trench.

That's not a deep trench - 3 feet is less than 1m. And he wasn't fully buried, just his foot and lower leg. But even with the help of paramedics, they could not get the man, or his injured foot, out of the trench. They had to call for additional help from firefighters to get him out.

In this case, it was a foot that was buried. But imagine if the worker had been kneeling down or crouching in that trench when it collapsed. He would of almost certainly died. Either from the weight of the earth crushing his rib cage or from suffocating due to the time it took to dig him out.

Again, this trench was less than 1m deep.

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.

What is the 1.2m excavation rule?

There is no 1.2m excavation rule!

It's not exactly a health and safety myth - because it did exist as a rule, decades ago.

HSE told NCE that the 1.2m rule appears in “prescriptive” regulations from 1966 but not in newer regulations published in 1996 and 2007, which are − like most modern health and safety legislation − “goal setting, not prescriptive”.

The basis of the original 1.2m excavation rule was 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.

The problem is that this rule is still quoted on sites today. It's been passed down from generation to generation because it was once true.

And people think this rule helps them! "It's under 1.2m so we don't need to worry about paperwork, risk assessments, and support - we can go ahead and get on with our job!" But instead of helping, this incorrect assumption could seriously hurt, or kill them.

This decades-old and long-removed rule is not something that should be considered when deciding if an excavation should be supported. The 1.2m rule is not in any of the current regulations, and looking at the article regarding the 3-foot trench, it is easy to see why.

Why was the 1.2m excavation rule removed?

The problem with the 1.2m excavation rule, is that it was a one size fits all approach. It didn't take into account different ground conditions, weather conditions, activities, and materials.

Excavations under 1.2m are not more stable.

Imagine digging a 1m hole in the sand. Would you expect the sides to cave in? Maybe if the sand is wet and compact, but as it dries out, or someone walks past, the chances of collapse are high.

An excavation that's 1m deep can collapse as easily as one that's 1.5m. It's not as though 1.2m is a magic height above which the ground becomes unstable.

Excavations under 1.2m are not safer.

A cubic metre of soil can weigh a tonne.

If you are standing up and the trench collapses, maybe you would survive. But often, workers within trenches may be kneeling down to carry out work, laying blocks, and installing pipes or cables.

If the sides cave in at 1.2m, workers on their knees could easily be buried. And with a tonne (or more) of earth on top of them, the chances of surviving are slim.

There is almost no ground that can be relied upon to stand unsupported in all circumstances and the risk is self-evident when you consider that it is quite common for one cubic metre of soil to collapse into an unsupported excavation, and this can weigh as much as one tonne.

At what depth is an unsupported excavation safe?

1.2m is no longer the threshold for the need to support an excavation, so what is the new threshold? Well, there isn't one.

There is no maximum depth for an unsupported excavation.

Current health and safety regulations tend to not generalise. They don't give a specific depth for needing trench support. Because each site is different. Different hazards, different conditions, different ground. What is safe and perfectly acceptable on one site, may be dangerous on another.

Need to carry out an excavation inspection? Use the Excavation Safety Inspection template to check your access, stability, conditions, vehicles, personnel and documentation.

Maybe on your site, the excavation might not present a danger. But you can only know this when it is assessed by someone competent to determine what controls are needed.

No excavation should be assumed safe, no matter how shallow. The need to support an excavation very much depends on ground conditions and other risk factors.

Prevent collapse – shore, step or batter back. Don’t assume ground will stand unsupported.

Shallow excavations are not safe excavations. Often, workers within trenches may be kneeling down to carry out work, laying blocks, and installing pipes or cables. If the sides of the excavation are higher than a person lying down, they could easily be buried.

And it could take hours to dig them out. It's difficult to dig quickly when the ground around you is collapsing, and you are trying to avoid hitting a buried person with your spade!

Trench collapses regularly make the headlines, and there are numerous court cases for collapsed excavations leading to injuries and deaths every year.

According to the Building Safety Group (BSG), the number of unsafe excavations grew 7% in 2017, with 408 excavation work breaches.

In 2018 a worker was trapped for over 6 hours in a collapsed trench. In 2021 contractors were fined for a trench collapse that crushed an employee.

And while excavation work mostly happens in construction work, the TV show Top Gear was accused of unsafe excavation practices.

When should an excavation be supported?

Just because there is no maximum depth for an unsupported excavation, doesn't mean every excavation must be supported. It means you might need support at any depth.

And excavation support can include:

• Battering the sides
• Timber supports
• Trench boxes
• Trench sheets
• Props
• Hydraulic bracing and struts

You need someone competent to assess if an excavation is safe, and what (if any) support it needs.

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 considered.

What is safe one day might not be safe the following week. If the ground dries out, it may be more likely to crumble. In heavy rainfall and wet weather, water may put additional pressure on the sides of an excavation.

Legally, you must prevent danger to workers in or near excavations and prevent any excavation, of any depth, from collapsing.

The Construction (Design and Management) Regulations apply to excavations and have some specific requirements in Part 4 - Regulation 22.

This includes the need to support and inspect excavations.

22.—(1) All practicable steps must be taken to prevent danger to any person, including, where necessary, the provision of supports or battering, to ensure that—

1. no excavation or part of an excavation collapses;
2. no material forming the walls or roof of, or adjacent to, any excavation is dislodged or falls; and
3. no person is buried or trapped in an excavation by material which is dislodged or falls.

In addition to requiring excavation supports, the CDM regulations also make it a legal requirement for excavations to be inspected before and during use.

The CDM Regulations don't specify a height at which support is required. As we have discovered, even shallow excavations can be dangerous, and even deadly.

---

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

Download the free excavations toolbox talk to spread the message to your team. You can 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.