hi sally, the question should not be a safe depth but the risk associated with the excavation. If we look at a greenfield site and a brownfield chemical site, the latter would obviously have more hazards present. I use to work around impacted contaminated ground and entering a trench in contaminated ground condition would need more than just gas detection, however the answer to your question on a known contaminated ground site - use a gas detector (for the gases/vapour you will be exposed to - so you need to be aware of possible chemicals and previous use) at all times regardless of depth. On a non-contaminated site (how can you prove this is the first question you need to ask), you may decide that after assessing the risks there would be no need for a gas detector for such a shallow depth (i.e no ground water, no utilities, greenfield site etc.) Although I would always use the hierarchy of controls and avoid entering into the trench in the first instance regardless it is green or brownfield. hope this helps Regards Derran

From the quoted size of your hole, it's not obvious to me how someone in it could bend down and get their head below ground. If all breathing is in the open air, can you foresee any hazard at all? To add to the point, 4ft/1.2m is a typical standard depth below which, in a longer trench, confined space precautions should be considered in a brownfield or operating site with potential flammable releases or ground contamination. So if your max. depth is 1.2m, even if the hole was wider, then a significant hazard is pretty unlikely - and published guidance like OSHA could be used to justify that?

Thanks guys, appreciate all the comments and advice.