Firemen's breathing sets

[Anthony Appleyard]

Most firemen's breathing sets seem to be roughly like modern air scuba, but the cylinder valves are at the bottom, and it has a fullface mask with second-stage built in, and no octopus regulator.

I found in internet image of a fireman, in an action pose with parts of his breathing set hidden by his right arm: the cylinder looked standard for firemen's, but from the fullface mask a single wide corrugated tube like on some gasmasks went down and disappeared behind his half-raised right arm. Was it going to a second-stage regulator strapped to his chest?

[hbhobby]

what you saw was most likley an older model that had a low pressure hose to the facemask, and yes it did go to a regulator that reduced the pressure down. the newer ones are very simular to a scuba setup with a high pressure hose up to the facemask. the major difference between a fire SCBA and SCUBA is the SCUBA's ability to change the pressure of delivered air to that of the surrounding water pressure. with a fire SCBA it is a constant positive pressure (meaning that if the seal around the facemask is compramised it will free flow) which keep one from inhailing smoke or other toxic "yuk" in the case of accidental compromise of the seal. The reason the bottles are positioned witht eh valve down it when crawling through "crap" it is less likely to get tangeled up if nice and round and smooth as opposed to a valve sticking up.
someone correct me if I am wrong on this part as I am not a SCBA technician but I do not think they have a first stage/second stage set up I think there is only one "stage" since when fighting fire there is very little change in ambient pressure around the individual.

[diversteve]

More than you probably want to know about them can be found here:
Self-contained breathing apparatus - Wikipedia, the free encyclopedia

[muddiver]

hbhobby is pretty much right on the mark. And no they don't work in the water. It has been tested by some of the local fire departments I worked with in the past.

[Anthony Appleyard]

... the major difference between a fire SCBA and SCUBA is the SCUBA's ability to change the pressure of delivered air to that of the surrounding water pressure. with a fire SCBA it is a constant positive pressure (meaning that if the seal around the facemask is compromised it will free flow) which keep one from inhailing smoke or other toxic "yuk" in the case of accidental compromise of the seal. ... I think there is only one "stage" since when fighting fire there is very little change in ambient pressure around the individual.

If "with a fire SCBA it is a constant positive pressure", how does a fireman's SCBA cope with changes in external pressure caused by?:-
*Weather: here in England I have seen weather chart pressures between 960 and 1050 millibars, and 50 mbar is about half a meter of water depth.
*Altitude: what happens when this sort of fireman's SCBA is used e.g. on the Peru and Bolivia Altiplano where the atmospheric pressure at ground level is not much more than 500 mbar (= 5 meters of water depth difference)?

[hbhobby]

the units are calibrated for their area of use. also the difference in a thousand feet of elevation in air are insignificant to the difference of a few feet in water. the difference from 960 milibars to 1050 milibars is only about 2 psi. therefore a SCBA which is set to have 4 psi(I could be wrong on the actual pressure but I believe I read somewhere 4 psi) would still work fine in fact if it was set for the 1050 milibars setting it would work better. also a major difference is you are losing ambiant pressure (when you go up in altitude) thus allowing for MORE free flow not less air availibility (which is what happens when you go under water with the unit.)

so a firemans SCBA will work under water to a certain depth (not very deep) then the ambiant water pressure will be greater than that of the SCBA and then you will get less and less air (kind of like the 30 foot snorkle thread)

[nips]

there actually is 2 stages. The bottles my department uses are 4500 psi, the first stage reduces it to about 100. The second stage attached to the mask brings it down to 15.

[truck1]

hbhobby is pretty much right on the mark. And no they don't work in the water. It has been tested by some of the local fire departments I worked with in the past.

Scotts will. Seen it done a few times with the newer versions.Even had the Scott tech tell us about a few that came in from that test and they worked fine in shallow water.No more than 10 feet or so.Past that mark(Unoficially of course) the electronics seals will leak.

[truck1]

there actually is 2 stages. The bottles my department uses are 4500 psi, the first stage reduces it to about 100. The second stage attached to the mask brings it down to 15.

The 2216 and the 3000psi packs did the same thing.1st stage was around 100psi, and the regulator was aprox 15psi.PCFD had and still has several on the rescue for airbags and airtools.

The bmr or belt/chest(in the case of the old scotts) are now outlawed by NFPA.All of the new packs from I forget what year, have to be mask mounted regulators.(mmr)

[Anthony Appleyard]

... the major difference between a fire SCBA and SCUBA is the SCUBA's ability to change the pressure of delivered air to that of the surrounding water pressure. with a fire SCBA it is a constant positive pressure ....

In that sort of fire SCBA does the "wet" side of the regulator diaphragm face a sealed pressure chamber rather than open air/water? How easy would it be to open that sealed pressure chamber to the outside?

Likely in firefighting, any sort of wide soft flexible "over the shoulder" breathing tubes would get in the way of rescuing someone carrying him over your shoulder.