The bulletin states:
Never work beneath a vehicle that is only supported on jacks. Use axle stands that are in good condition and inspected every year. Use stands on firm, level ground and securely located under a strong point on the vehicle. Securely chock wheels remaining on the ground. Do not exceed the rated capacity of the stand.
Never work beneath a cab or tipping trailer unless it is propped. Always prop cabs, trailers etc that could drop under their own weight. The prop should be locked in position before gaining access. If there is no prop fitted, or if one is fitted but you are unsure it will be effective, provide your own.
Never crawl beneath a vehicle fitted with air suspension unless it is properly supported. Prevent movement of air suspension, either by using suitably rated props or stands to prevent the chassis lowering or by deflating the system. Don’t tamper with the ride height for the purpose of recovery or repair.
Further information is available in the HSE publication Working safely under motor vehicles being repaired (INDG434) which is available via https://is.gd/nikitu
You can also find out more in the HSE’s safety alert (issued May 2020) about air suspension systems on vehicles available via https://is.gd/munoxu.