 | Boiling Point No. 07 - December 1984 |
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Danger Signals to Human Health
by W.F. Sulilatu - Woodburning Stove Group, The Netherlands
TOXIC ASPECTS OF CARE ON MONOXIDE
Carbon monoxide is a product of incomplete combustion. It is a colourless, essentially odourless and a highly poisonous gas.
Assuming that the average oxygen content in the lungs is about 15%, Fig. 1 presents the relationship between COHb and CO for an equilibrium situation. It also shows the symptoms related to the various COHb contents in the broad.
Fig. 1 CO Hb content of the blood in an equilibrium situation for various CO concentrations in the atmosphere
Concentration calculations
In view of the foregoing it would be interesting to calculate the carbon monoxide pollution caused by using a stove in an enclosed space. The calculations have been made for a stove with a poor combustion performance tested by the WSG and for space volumes of 10 and 40 cubic metres. The e air exchange rates were assumed to be 2 and 4 respectively which in general are considered as natural ventilation rates. However, it can be argued whether the used values can apply to circumstances prevailing in developing countries.
The power output of the stove was 4 kW and the CO and CO concentrations in the combustion gases 8.8% and 0.8%
The results of the calculated CO concentrations are presented in Fig. 2 which shows the increase of the CO concentration in the atmosphere as a function of time. Also depicted is the boundary line of the maximum allowable CO concentration (MAC) as a function of the exposure time. The Figure shows that at a CO concentration of 0.05% in the atmosphere the maximum allowable exposure time is 9 minutes. It also shows the dramatic effects of lowering the air exchange rates and reduction of the space volumes.
Fig. 2: Build up of the carbon monoxide concentration as a function of time calculated for various air exchange rates (R) and space volume (V).
Depending on the activities of the people concerned. the allowable exposure times will be different. A working person for example can only be exposed to a certain CO concentration for one third of the time Of a person at rest (Fig. 3).
Fig. 3: Limitations of the carbon monoxide concentration as a function of the exposure time.
Woodstove designers are well aware of the necessity of reducing the CO emission. Reducing it to zero would be the solution, for the time being however this is still unattainable. So the question now has to be answered as to what is an acceptable CO source emission. Viewed in this light it would be significant to collect information concerning kitchen volumes and air exchange rates in developing countries. For those places in the world where stoves are normally used for overnight heating the importance of this information is quite obvious. Using this data combined with extended data from research in the laboratory a standard source emission can undoubtedly be established.
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