Posted By Ken Taylor I've not seen a definition of this either but have applied it to live-working on electricity.

Posted By Gary Levers Hi Richard, For the purposes of interpretation, I would consider it to be equivalent to ‘significant risk’. If I remember correctly, regulation 6 - measures relating to night time working, refers to "special hazards" or heavy physical strain or mental strain. With regard to night work we had to consider whether the work attracted any "special hazards" associated with night time working. For example, did the task may become more difficult: 1) when performed at night in darkness rather than in daylight; 2) when the full range of daytime services were not available; or 3) due to a change in a worker's work/sleep pattern. I have e-mailed you directly a source of info I used Hope this helps Gary