Much of what you smell when you work is burnt oxygen.
Umm. time for a little chemistry. Oxygen doesn’t burn. It causes
other things to burn. In the case of the fuel gasses going through a
torch, your normal combustion products are carbon dioxide (fully
burnt fuel gas) carbon monoxide (partially burnt fuel gas) and water
(the product of buring the hydrogen in these hyrocarbon (hydrogen and
carbon) fuels like propane, acetylene, natural gas, etc. None of
these have any smell whatsoever. Carbon monoxide can be toxic if it
builds up, but it doesn’t smell at all. If you’re smelling things at
all, it’s not burnt oxygen (can’t be, there’s no such thing), and
probably not the burned fuel gas either. It rather, will be UNBURNED
or PARTIALLY BURNED componants, probably trace organic impurities,
from either the fuel gas, or more likely, given off by the items
you’re heating with the flame. Working in a closed room can deplete
oxygen, but more likely, you’ll react sooner to the excess of carbon
dioxide and, if there is any, carbon monoxide given off by the flame
than from any actual depletion of oxygen, since it takes a lot less
CO2 in the air to cause feelings of distress than you feel from lack
of oxygen. You can deplete a goodly percentage of the oxygen before
you’ll start to suffer from it, and the symptoms can be subtle.
Sleepiness,headache, lack of concentration… Same as altitude
sickness. If you have trouble with such symptoms when on aircraft
(pressureized usually to about the 8000 foot level, which means a
reduction in atmospheric pressure of about, if I recall right, 1/4 to
1/3 sea level pressure, along with the same reduction in the amount
of oxygen, then you might indeed be feeling a lack of oxygen. But in
order to deplete that much oxygen from a room, you’d have to convert
it to the combustion products. some water, and some CO2. That much
CO2 in the room will most definately make you feel sick.
As to the smells, organic materials especially, when heated below
the point where they burn, can give off strong smelling componants.
Oils from fingers, on the glass you work, for example. Or various
other componants of what you’re heating (fluxes used in soldering)
can also release airborne componants which smell. And fuel gasses
(propane, acetylene, natural gas) usually have strong smelling
additives which are put there specifically so you can more easily
detect a leak, since the pure gas itself may not have a strong
smell. These additives will still leave some smell if they are not
completely destroyed in the burning flame.
Note that both oxygen and CO2 will dissipate relatively quickly
through the air, so to keep a room reasonably well ventilated in
terms of enough oxygen and getting the CO2 out, you need usually only
be sure the door is open, unless you’re using really large flames.
This may NOT, however, be enough ventilation for the more noxious
products of the process, such as flux fumes or the like.