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Skip to content Skip to navigation. Health and Safety Executive. Home News. Text size: A - switch to normal size A - switch to large size A - switch to larger size. Bookmark Print Register Login. Could anyone please advise me on the current Health and Safety position legal, best practice or otherwise regarding 'shallow' excavations? This makes reference to the idea of 'self supporting' ground whatever that is! However my understanding of the new 'Working at Height' regulation is that these apply to excavations - working below ground is classed as 'work at height' - and any level difference is potentially a height.
Consequently the often used industry measure of 4 feet or 1. I worked as a temporary works designer for several years and never came across any soil analysis methods that are able to demonstrate the stability of unsupported vertically sided excavations in anything other than unfissured, monolithic rock. Maybe design techniques have moved on but without this as the starting point the only other way of managing such constructions is via risk assessment.
However with no technical basis such assessment would have to assume the sides of the excavation will, at the very least, partially collapse at some point. Not a very satisfactory assumption for any one set to work in the trench or indeed standing near the top and whilst some might say a shallow depth, say mm, won't be an issue this could easily cause someone to twist an ankle or knee if they were pitched forward into it without warning.
As a consequence therefore my own conclusion is that the only way of being 'guaranteeably' right as a Designer or Principal Contractor from a CDM perspective is to ensure pretty much any excavation 'shallow' or otherwise is either provided with some support trench sheets, props, drag boxes etc or the sides are sloped to a stable angle.
Such approach seems to be very extreme and impractical and is at odds with a significant number of current site practices I've come across. Your thoughts would be welcome. A Civil Engineer will be able to determine the acceptable safe angle of repose for various soils through basic calculation and soil mechanics. You cannot possibly provide support for all excavations eg.
As every excavation will expose different ground conditions, different depths of dig, different lengths of exposure and different weather conditions, each must be assessed seperately by an Engineer or competent person , who will assess the structural properties of the soil and look at things such as adjacent loading eg - is there any spoil or plant or equipment near the excavation that add loading to the sides.
This person will then decide what support if any is required. Hello, My interpretation of the Working Height Regs relative excavations is to the prevention of persons falling in to them, as a hole to a person on the surface is a 'height' and of course the prevention of a fall further in to the excavation should a person be working at a height below ground level but not at the actual bottom of the excavation. I don't think the above regs are anything to do with the collapse of an excavation.
I beleive that this requirement is covered by CDM 07 Reg I am sure there is loads of advise on the HSE web site with regard to the 'battering', 'stepping' etc. Am I right or wrong guys? I agree with Jim, You can over complicate, treat them a seperate issues, protecting excavations will negate any 'working at height' problems associated with them.
And address any work at height as you would normally. I don't suppose it would matter to the bloke falling from the 3rd level of scaffolding whether or not he stopped at ground level or continued a little further into a shallow excavation! Hi Guys Just to throw another excavation problem in.
With regards to spoil etc, I tend to agree with the chap who says you can over complicate. Each job should be risk assessed, taking into account the type of spoil, site environment, plant etc. As a Company, we state that excavations under 1. For excavations over this, at least 1 metre from the edge. God help me - I cant stand much more of this rubbish from the discussion forum - jumping in and out????
Reg, I have been following this thread to see if I can learn anything, not being 'in the trade' so to speak, what would you suggest is the answer? Thanking you in anticipation Regards Mitch. Chris, I agree that it is easy to over complicate these things - which is where your risk assessment comes in. However, it takes a competent person to understand and assess each excavation. For example, the spoil from a typical mm wide trench at a depth of 1.
So the assessment should be if the type of ground can support the weight of a small car immediately adjacent to the trench. A lot of interesting arguments but surely need to look at risk of injury, not just risk of collapse.
As the first poster rightly identified no soil is fully stable with vertical sides and any depth of vertical trench in soil is guaranteed to collapse sooner or later till it comes to its angle of repose.
This angle of repose is not reached immediately except in classic granular materials - cohesive soil will take longer to collapse.
But to rely on the time - movement characteristics you would need a very high level of competence to recognise the ground conditions accurately. There are three ways you could be harmed by a collapsing trench - by being buried - by falling in with the soil - or by the collapsing trench causing buildings materials or plant to fall over.
So in using an unsupported trench would need to ensure 1. But even then need to consider how and by whom would the operative be extracted? Remember to consider if they need to bend down into the trench eg to make pipe connections, when they could still be completely buried by a shallow trench.
The 1. But it is certainly not a safe limit in all circumstances. Finally remember current industry practice is not necessarily best practice! Well found! The hse guide is excellent in most respects but it is slightly out of date on working at height - it implies the old 2 m rule which is no longer acceptable. I had this publication, and was just watching the discussion to see how it developed. The controlling height for a full working platform with all guards etc.
And there was me thinking that 'suitable control measures' were required if a fall from height had the potential to cause an injury regardless of if was below 2 metres or not.
Thanks for enlightening me. I think I have missed something I thought 12 refers to inspection. My understanding is that there is still a responsibility as pointed out by Paul?
This would need to be assessed dependant upon the scenario, type of excavation in relation to other activitites taking place whether that involves platforms, ladders, blockwork etc this may or may not involve WAH which is seperate from the requirements of excavations. I would appreciate any clarification that anyone can give on this.
However, falls from any height need to be guarded against as per reg 6 3 - - - suitable and sufficient measures to prevent - - - - any person falling a distance liable to cause personal injury. Construction information sheet No 10 Rev 4 Tower Scaffolds - - - - -the requirements for inspection is different for small towers under 2m, and for towers of 2 m and above, a working platform less than 2m in height, the tower must be inspected after assembly in any position after any event that may have affected its stability at suitable intervals depending on use a working platform 2m or more in height, it must be inspected after assembly in any position after any event that may have affected its stability at intervals no exceeding seven days But hey!
A thick welder!! I used to be a welder, but I'm alright now. I once fell onto a concrete floor from a scaffold of about 2 metres high, not a nice experience believe me.. I'd forget about the 2m limit if i were you. Regards, NPG.
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A guide to safe practice in the design and use of temporary support for trenches not deeper than 6 metres, intended for the use of designers both of permanent and of temporary works, temporary works co-ordinators and supervisors, estimators and planning engineers. It covers the identification of basic information about the ground and proposed works that is essential for the design of proper supports; the choice of appropriate support systems and methods of groundwater control; simple methods for the design of struts and walings; the procedures for installing and withdrawing supports, and check lists for design, planning and day-to-day supervision of the works. Throughout there is an emphasis on safe design and methods of work, and particular dangers are highlighted. Appendixes are provided on legal requirements, properties of timber, an extract from the Construction Regulations , a specimen certificate of exemption for excavation plant used for lifting, and a safety checklist for supervisors. Toggle navigation Menu. Availability: Find a library where document is available.
Latest version of document. Guide to safe practice in the design and use of temporary support for trenches not deeper than 6 metres. Intended for the use of designers both of permanent and temporary works, temporary works co-ordinators and supervisors estimators and planning engineers. Covers identification of basic information about the ground and proposed works that is essential for the design of proper supports; the choice of appropriate support systems and methods of groundwater control; simple methods for the design of struts and walings; procedures for installing and withdrawing supports, and check lists for design, planning and day-to-day supervision of the works.
REP R 97 Trenching practice. 2nd edition (2001 revision)
TRENCHING PRACTICE - 2ND EDITION