My interpretation is similar to yours CJK. A fire will always have the potential to place people in serious and imminent danger from the direct effects of fire smoke and toxic by products of combustion. Article 15 requires the responsible person to ensure that having eliminated or reduced the risk of fire occurring, he has procedures in place to ensure that relevant persons are able to leave the area involved, by their own efforts (or with assistance provided by the responsible person) in order to avoid the danger.
But some areas offer an even greater risk from fire due to the processes or substances present there, and may present risk of explosion. The procedures necessary to ensure the safety of relevant persons arising in these high risk areas will need to be more effective and robust, for example to allow more rapid escape or earlier warning of danger.
Procedures will therefore be appropriate to the level of risk.
This requirement is of course an echo of the similar requirement in the management regs and the coshh regs and has to be specifically re-iterated in the RRO as a result of article 47.