This is definitely one of those of "how deep does the rabbit hole go?!" in terms of the background for the area in question. It all started with an innocent question from a client about an old poster in their UPS battery room about "Electric Accumulator Regulations 1925". Initially it was found this has been fully revoked by the Control of Lead at Work Regulations 1998 then 2002, however these only appear to cover the use of lead in the construction of the battery cells. Which leads us to Electricity at Work and MSDS/COSHH controls for the acid in the batteries. However, as the batteries have the potential to generate hydrogen gas which could form an explosive atmosphere if batteries were breached this is where DSEAR comes into things. Could any of my colleagues suggest the best next step with this that I can provide to the client, though my basic understanding of DSEAR is that an assessment needs to be carried out and an action plan put into place. Signs are already in place with appropriate warning symbols (explosive and no naked lights) as well as word version of the warning symbols. The room is fire rated but I am unsure about the FR level. Would these controls be seen as sufficient as long as there is an assessment/plan in place as well to meet DSEAR?

It's a separate UPS battery room with the UPS control modules in a completely different part of the building. I've requested a specification sheet from the company replacing the batteries but I'm guessing from weight/size and previous batteries in the room they are lead/acid as the gel based batteries I've used previously are lighter for the same size.

Thanks Safety Smurf, just got the data sheets and while they are an acid based battery they are completely sealed and design apparently ensures recombination of generated hydrogen and oxygen is maximised. However they do have pressure relief valves (i.e. unless build up of gas is sudden and in large quantities unlikely to breach the individual cell). As the manufacturer states that they do not need a separate battery room (can be installed in cabinets or normal UPS module stands) then it seems that they are unlikely to cause potential DSEAR issues. Though as you say numbers may be a factor. I'll check the construction of the room/ventilation to be sure.