Peter Wardle is right in that there is no 'safe' recommended depth for excavations. It just has to be safe.
The IFA does not issue guidelines for safe depth of working. I believe that their Code of Conduct insists that IFA members have due regard to Health and Safety legislation.
As for entrenching tools. A few years back we tried to use these on site. It was pointed out to us by our Health and Safety advisor at the time (also one do the authors of the SCAUM H&S manual) that there was a tendency to use these tools at face level and if there was a rebound from a hard surface the pointed 'back end' of the tool was likely to cause serious damage to someones face. A secondary factor was that as these tools tend to be picked up secondhand you have no idea of its previous history and as we found, the shafts tend to break at inappropriate moments.
I would ask Nick to seriously consider whether the use of these tools is worthwhile.
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