Posted By Stephen J W Clegg. I was fortunate enough to attend a ‘burn’ recently, it was a joint venture arranged by our local Fire Service and the L/A. The exercise was carried out in both sides of a semi-detached property… to cut to the chase, your question was asked by a few people. There are various types of sprinkler head available on the market, all the ones shown to us and used on the day fit flush to the ceiling. The basic design is based on the traditional concept i.e. activated by heat. The flush fitting cap that covers the unit is soldered on in three places, so in theory it might be possible to melt the solder in one of the three places… trouble with this is, the melting point of solder is around 190 degrees centigrade. If a person were to hold a lighter or other source of heat under it for the length of time needed to melt it, by the time he/she moved onto the next point, the melted solder would have ‘re-set’ and the cap would be in it’s original position and fixed. The manufacturers did say though that if a person was so intent on setting off the system deliberately, they would do by what ever means were available… it is worth noting though that throughout the Greater Manchester area, there have been no reported deliberate activations of this type of system. Another benefit of fitting this type of system is that insurance premiums could be reduced. Good luck with this one! Regards Steve.