Hello boys and girls, its been a long time since I posted due to a techie problem with the site, but i have been marking your homework.....
Test Gas
I have discussed this in the past at Director level with most of the detector manufacturers and the original problem of the residue was solved by the later test gas. My understanding of the present situation is a potential problem with the properties of the propelant gas in the can. In large quantities this can have a detrimental effect on the waterproof membrane ( varnish) painted on the detector pcb during manufacture to enhance the environmental protection of the board and components.
wow what a gob full that was. In short: dont keep spraying the tester in the head if it wont go off or eventually you won't be able to stop it going off on it's own!!
Dave