Diesel Engine Emissions. Diesel smoke test equipment will be considered suitable if the following is provided a) a calibrated diesel smoke meter on DVSA's latest List of Acceptable Equipment b) smoke meter user/operator instructions. 6. Class 3 Only Testing. Where only Class 3 testing is conducted the requirements for Class 4 are varied as follows 6.1 Premises, Test Bay and Equipment Layout. a) Premises (No variations) b) Test Bay Vehicle entrances and exits at least m wide and m high Bay width at least m Bay headroom at least m Headroom over a lift of at least m c) Equipment layout With a clearance of at least mm to the front and rear of a lift or pit to any entrance/exit door or wall.