Of all the dodgy things your workmates might get up to at home - and, let's face it, the options don't bear thinking about - drug-use is possibly the only one which could have a direct impact on your safety.
Experts say people recovering from some quality time with their P-pipe, or hanging out for their next session, could be erratic, jumpy, careless, paranoid or nursing a particularly short fuse.
Add heavy machinery and deadline pressure, and that work colleague becomes a frightening liability.
When you consider the vast majority of workers commute along busy roads to get to and from work, the risks for the whole community are evident.
New Zealand Drug Detection Agency figures show of the 401 Western Bay employees who tested positive for drugs in the past year, 21 per cent - or 84 people - had amphetamine-type substances such as ecstasy or methamphetamine, which is known as P, in their system.