ZQA297/30
There are 2 Criminal Offences now...One has to do with impairment, the other does not.
Legislation came in earlier this year, which is the RAILWAYS and TRANSPORT SAFETY ACT 2003
There are 2 offences related to drinking contained in it.
Section 92. Being unfit for duty. This is what it implies, being unfit is not capable of doing your job due to alcohol (or Drugs).
The new act is related to drink driving offences in the Road Traffic Acts. In that, (in section 92)the initial suspicision that normaly leads to arrest is a Constables opinon. To some extent thats subjective, but he would be looking for impairment. Basicly when I was a baby Policeman I was told if he falls out of the car nick him for being unfit. Otherwise.....
The other section is Section 93. This has nothing to do with impairment, just that you try to do your job with a Blood Alcohol Concentration above a prescribed limit. That limit is set in the act as 20 milligrammes of alcohol in 100 millilitres. That represents 1/4 of the drinking and driving prescribed limit.
There does not have to be evidence of impairment, and you can be breath tested (the same as you can be in drink driving cases) by a constable if he suspects you are on duty with a BAC above the limit, or if you are involved in an accident or involved in an incident.
The suspicision can come from many things, the way someone acts, a smell (and not just of alcohol, mints is a give away) or having just seen the person down a pint. The intial suspcision could also come from someone else, ie, bus driver smelling what he thinks is alcohol and calls Police. They turn up, smell alcohol which then gives the Constable reason to suspect that he may be commiting the offence thus giving reason to breath test. It is as a result of that breath test that you would be arrested, not as the result of what the driver of a bus thinks.
On having Breath/Blood or urine tested at a Police station the person would then either be charged and appear at court, or if the BAC are below the limit released. As with Stocks and shares, BAC goes up as well as down. Have 3 pints and BAC will continue to rise for some time afterwards....Then go down.
There is no way of reliably telling how fast the alcohol gets out of your system. And this section is NOT related to impairment.