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In the second of our regular columns, the experts from NEBOSH answer our readers’ occupational health, safety and environmental questions.
We are about to start doing some excavation work and I wanted to know how to stay safe on-site. Do you have any tips that will help us?
Excavation is a hazardous part of construction work. It presents a series of risks to workers that must be addressed to keep everyone safe. We’ll look at just some of the principles of excavation safety.
The risk of collapse
Common dangers include collapses, falling loads, striking underground pipes, hazardous atmospheres and mobile equipment. However, cave-ins or collapses pose the greatest risk to workers and are the most likely type of incident to occur.
One cubic metre of soil weighs about 1.5 tonnes, so you can imagine the implications if someone was trapped, even under a small collapse.
One thing to remember is that you cannot rely on an excavated trench (of any significant depth) supporting itself. It will collapse unless it is supported in some way. So, before any digging takes place, you must decide what temporary trench support you need to use. For example, drag boxes / trench boxes, timber supports, trench sheets, battering the trench side back, depending on the nature of the soil and size/depth of the trench. Make sure these are readily available on site before any work is started. You also need to take precautions to ensure the smooth running of the project and implement plans (including rescue) in case an incident was to occur. This includes identifying appropriate site access, regular inspections, locating underground pipes/wires and overhead cables.
Day-to-day excavation activities also pose a significant risk. Falling or dislodged material is something you need to watch out for. The movement of equipment or vehicles near the edge of the excavation site could easily cause material to slip, so store them away from the edges and move them carefully, if necessary. Use edge protection, including toe boards, projecting trench sheets or box sides, all of which help guard against falling materials.
Depending on the site conditions, it is possible that the trench may fill with hazardous vapours. If you are working in a trench deeper than about 1.2 metres and in an area where hazardous atmospheres are likely, atmospheric testing, ventilation, and respiratory protection, should be provided. Workers who ‘rush’ in to rescue co-workers, often become the victims. Many workers who die from such atmospheres are would-be rescuers themselves, so make sure your staff have the right skills in place to handle situations like these. This type of site should, however, be identified early on, when planners perform pre-construction site surveys, so you know to be alert and prepare your employees accordingly.
Inspections
No work should take place until a competent person has inspected the site at the start of each shift. This might sound obvious, but you would be surprised how often it gets overlooked or dismissed as a formality. It’s important not to cut corners – the well-being of staff is more important than anything else.
All excavations should also be inspected after an ‘event’ that might affect its strength or stability. This would include the use of big machinery, or after a falling rock or large movement of earth. It’s important that a detailed record of inspections is kept, with any faults being corrected immediately.
Worker training
People make one of the biggest contributions to day-to-day safety. It’s important that all workers know how to stay safe and, in the event of an incident, know what to do.
The information here is a snapshot of tips to help you and your team stay safe. Of course, there is a wide range of training and qualifications available to give people the skills they need to create a safe working environment. Our NEBOSH International Certificate in Construction Health and Safety covers a broad range of construction hazards – including excavation – and how to control them. What’s more, the practical element of the qualification gives students the opportunity to carry out a safety inspection and prepare a report – something that’s essential in creating a safe working environment.
For further information about NEBOSH and its qualifications, visit www.nebosh.org.uk
