An authorised person must not direct the rail safety worker under section 28 or 29 to provide a specimen of breath or saliva for analysis if—
(a) the worker gives the authorised person a prescribed medical certificate relating to providing that type of specimen; or
(b) the worker was not required to comply with a direction under division 3 to provide a specimen of that type for preliminary testing because the worker gave the authorised person who directed the worker under division 3 a prescribed medical certificate relating to providing that type of specimen.