Surely it would no longer be a decontamination unit. The purpose of it being to prevent fibres contaminating the air?

It is perfectly permissible to have the DCU separate from the asbestos enclosure, i.e. adopt a transiting situation but you have to give justification for this and ensure the correct control measures are used. Transit coveralls and footwear. Clear marking of the planned transit route. No unauthorised access to the route by non- asbestos personnel. Strict levels of monitoring along the route to ensure cleanliness. The four stage clearance process will include the transit route, etc. etc. In my own personal experience direct connection of the DCU to the working enclosure is very rare due to, for example, building layout & design, space restrictions, vehicular access, etc. There are modular portable DCUs on the market that do make it easier to make direct connection but the drawbacks are they are small (usually one shower, meaning 4 workers max.), they are less robust, more finnicky to clean. If direct connection can be made then great, just don't forget to include an intervening space between the airlock and the DCU itself. The HSE do not have a problem with transit routes as long as you justify the reason for them.

For information refer to HSG 247 Asbestos: The Licensed Contractors' Guide. Chapter eight deals with "Decontamination". Includes illustrations of DCU's both directly and indirectly attached to asbestos enclosures. While not entirely accurate (particularly with regard to the warning signs) this does give the definitive position. Rodger Ker