According to the Rail Industry Standard RIS-8070-TOM [9]

Positive result for drugs and alcohol testing 3.4.1A ‘positive result’ shall be confirmed when a test on an individual performing safety-critical tasks shows:

  • a) The presence of drugs with no legitimate medical need for their use or the quantity of their use;
  • b) More than 29 milligrams of alcohol in 100 millilitres of blood;
  • c) More than 13 micrograms of alcohol in 100 millilitres of breath; or
  • d) More than 39 milligrams of alcohol in 100 millilitres of urine.

Individual transport operators may choose to adopt more restrictive levels

Note, Scotland [10] has the ability to set its own limits for railway safety critical staff. However, they are currently aligned to the Transport and Works Act 1992 [4]:

  • Blood alcohol: 80 milligrams in 100 millilitres
  • Breath: 35 micrograms in 100 millilitres
  • Urine: 107 milligrams in 100 millilitres

Safety critical in this sense includes:

  • Drivers
  • Guards
  • Conductors
  • Signalmen
  • Maintenance
  • Supervisors
  • Look-outs
  • Anyone who can control of affect the movement of a vehicle