know pretty much nowt about firefighters and pacemakers but had a case a while back where the magnetic locking system in a secure environment was knocking out an employees pacemaker settings, as was being wanded down on a daily basis. Thus ensued much argy-bargy between the lock manufacturers/H&S/me. The science bit from the manufacturer was that every day household items like hoovers, hairdriers etc emitted more of a magnetic field than their locking system (we did a big excel spreadsheet for comparison) so it couldnt be their problem, however I had objective evidence in the form of 24 hr ECG that something was going on and we could whittle it down to certain times of the day - indicating that it did. Upshot was that because the pacemaker was an "old" type there was the potential for it to be affected, if it was a newer one then it wouldnt have been a problem. A more recent case with a prison officer resulted in an opinion that direct trauma should not affect a pacemaker unless there was penetrating injury.  Not sure if this helps at all - all goes back to individual risk assessment, the type of pacemaker it is (eg on demand etc) and what the underlying pathology is I guess.....good luck!