Although I hate to be pessimistic about a good idea, I must
offer some cautionary feedback on B. R. Saubolle’s article
“How to Make and Use a Sawdust Stove” (MOTHER EARTH NEWS NO. 30). In
particular, I want to amplify a warning by the author that
the homemade stove “does give off some fumes” and that the room
where it’s in use “must be well ventilated”. Very true . .
. but the statement isn’t definite enough or strong enough.
Combustion in such a device might easily be incomplete,
and — instead of giving off only carbon dioxide and
water vapor, the gases normally associated with
burning — the smoldering fuel might also produce carbon
monoxide and hydrocarbon vapors.
The problem is that the combustion process isn’t as simple
as it might seem, particularly where wood wastes or other
complex hydrocarbon mixtures are concerned. For complete
burning, each molecule of such a substance must be broken
up (eventually into its elements . . . carbon, hydrogen,
sometimes oxygen, and others) and gasified (solids and
liquids don’t burn, but the gases formed from them at
elevated temperatures do). If gasification occurs before
the total breakdown of the particles, less complex
hydrocarbon molecules may be given off as vapors. Or, if
the original units do break up completely but don’t contact
sufficient oxygen to be fully oxidized, carbon (soot)
and/or carbon monoxide may be produced.
Both soot and hydrocarbon compounds are usually detectable
immediately, either by sight (black smoke) or smell
(solvent-like odors). Carbon monoxide, however, is odorless
and invisible.
The dangers of these incomplete combustion products vary with homemade stoves.
Soot is primarily a source of grime, but could cause
respiratory problems over long periods. (Once inhaled, the
minute carbon particles are deposited deep within the lungs
and will not be expelled by breathing.)
Hydrocarbon vapors will cause various problems depending on
what specific compounds are present. If any organic acids
or aldehydes are produced skin, eye, and respiratory
irritation would be likely.
The real killer, though, is carbon monoxide. This substance
has an affinity for the oxygen-carrying hemoglobin in the
blood which is some 210 times that of oxygen itself . . .
and its absorption through respiration therefore prevents
proper oxygen intake. Over long periods of continuous
exposure, more and more hemoglobin is “tied up” until the
bloodstream can no longer carry sufficient oxygen to
sustain life.
There’s really no way to determine the degree of incomplete
combustion — and corresponding danger — in a stove
such as the one described in the article. The device must
certainly be used with adequate ventilation, as the author
stated, but this might make it ineffective as a heat
source. At any rate, it would seem inadvisable to use the
non-vented heater in a sickroom or other area in which the
occupants are sleeping or incapacitated (I’m thinking
especially of babies and elderly persons). If combustion
were poor, one average night’s rest could turn into an
eternity.
The larger models of the stove appear safer, since a flue
would likely be used to vent any fumes. Nevertheless,
anyone who uses either this or the smaller heater for long
periods should immediately seek fresh air — preferably
outdoors — if headache or dizziness develops.
In case you’re wondering, I’m by no means an expert on
combustion. As a chemical engineer now working for a
government agency on air pollution control, however, I’m
often concerned with incineration and with the use of wood
waste as fuel . . . and I must emphasize one point:
Although various efforts have been made to control air
pollution from the burning of wood by controlling the
combustion process, such operations have proven very
tricky. With many types of combustion devices it’s possible
to reduce the amount of smoke produced, but not the amount
of carbon monoxide. Deaths from poisoning by this deadly
gas have resulted in the past from the use of charcoal as
an indoor fuel . . . and the principle of the sawdust stove
is very similar. I offer these comments in the hope of
preventing MOTHER’s readers from injuring themselves.
Although I have my doubts about the sawdust stove in the
form described, I thank B. R. Saubolle for sharing his
knowledge.
