Well I got 13 or so years on the job,my dept. has about 525 men.I would say about half don't carry any knife and the rest carry everything under the sun.Junk pos knock offs are popular,although some do see the light after they fail...
Sak's, and the Leatherman type tools are popular.Slowly but surly guys are turning to good one hand,clip type knives.Most want 50/50 but plain has a smaller but strong following.These tend to be CRKT,Gerber,spyderco and a few benchmades.
Myself,i carry a BM 710 or CRKT M-16FD and either a Meercat,Delica or SAK.
Uses,Well we live in a firehouse so anything you may cut at home we cut at work.This includes food prep.cardboard boxes,rags etc.
On calls I may cut open a smoldering mattress,cut away burned carpet,cut plastic or tar paper to cover vent holes.Then theres the getto padlock,you know when people tie their fence gates closed with rope or electric cord.
I never had a seat belt I could not simply unbuckle and quite frankly I don't like using sharp things in cramped crowded places with many people around some of them excited .
I also stopped long ago using knives to cut off clothes.Bad taste at shootings and stabbings and risky always.I've had more than one person come to and find a stranger(me) leaning over them amd become combative.This along with the fact that you got 2 -6 fireman plus the ambulance personnal working in some small bathroom or hallway,the last thing you need in there is a razor sharp knife.
Then theres the Detroit cop who cut a womans fingers while cutting off her sleeves who's being sued for 100 million They made a big deal out of the fact the knife is non-issue,theres no poilcy for using them etc.I think I'll stick to my dept. issued emt shears and seat belt cutters (if needed)for work around people.