Thats part of the logic behind the ADF's no drug policy....
If your on drugs or they can prove you have been (and its a big burden of proof but since most drugs leave tell tales for up to 3 months its not impossable)
If your idendified as being contributing thats it your toast, your toast anyway as drugs are an auto discharge thing.
in my experience most failures are repeatable, and if they dont there is generally other evidence that will back up a potential one off failure cause.
Last accident investigation I was involved in (2-3 weeks ago) had me stripping the wiring harness of a truck looking for anything that might have caused an indicator on a trailer not to flash.... (someone else was on the trailer) he found corroded contacts in the plug and I found a burnt contact in a relay that was otherwise working fine.... we couldnt make the system not indicate when used normally and we flooded the plugs, spritzed the relay box froze them, toasted them the works.
driver got off scot free for someone running into him who claimed he didnt see the indicators flash after the MP's determined that due to the nature of the turn the only indicator light he would have been able to see was the one on the back of the trailer.
if hed had a trace of anything in his system tho.... :(
Bit off topic but its a little evidence that some investigators will go to extrodinary lengths to make sure that a one off failure isnt missed. took us 40 manhours to check the indicator circut alone hell knows how many other hours went into it.

