It'd be reasonable to expect John to have some experience facing situations of this nature. Even if not identical, a similar situation is enough to avoid the irrational responses. As to Sherlock, well.. with his intentionally different personality, assuming he is better at managing that kind of situation than most is reasonable.
An explosive so delicate it would detonate from sliding across the flooring in there would be at a risk for detonation from the wearer's movements. That's not really practical for that sort of vest. There are very stable explosives that could be chosen (such as C4 - though since they're in the UK they might get PE4 instead). While there's a possibility a pulled wire could cause an issue, that's relatively unlikely with the flooring in there. However, water can interfere with circuits and cause the trigger to fire, which would then set off an otherwise more stable explosive. It's not that the explosive would respond to being wet, but the wiring. Being immersed in water is rather different from having water (sweat, rain, whatever) fall on the wiring, so a different response from the device is reasonable.
Last edited by equiraptor (February 14, 2013 1:10 am)