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The effect of ventilation on carbon monoxide and particulate levels in a test kitchen


Table of Contents

Boiling Point
Front cover of Boiling Point issue 52
Issue 52 (2006) Health, safety and household energy
ArticleThe effect of ventilation on carbon monoxide and particulate levels in a test kitchen
AuthorDean Still, Nordica MacCarty

[top] [end]Abstract

Concentrations of carbon monoxide (CO) and particulate matter were monitored in a test kitchen when differing levels of ventilation were introduced to the building. These included: all windows and doors closed; door open; a small hole cut in the roof; cross-ventilation to the hole in the roof provided by a small window. Each configuration was tested three times with a constant pollution source. Increasing amounts of ventilation significantly reduced the levels of carbon monoxide and particulate matter.

[top] [end]Introduction

Smoke from the combustion of biomass is found in nearly half of the kitchens in the world. Exposure to smoke has been associated with chronic obstructive lung diseases and acute lower respiratory infections. The WHO has estimated that, every year, about 1.5 million people die prematurely due to breathing smoke from this source. Although breathing carbon monoxide is dangerous, inhaling particulate matter is probably the single most important health-related constituent of wood smoke. (Naeher et al, 2005)

Data from a comprehensive study of 236 houses in Bangladesh suggests that fuel choice has a significant effect on the level of indoor air pollution. Cooking with cleaner burning liquid fuels results in generally lower levels of household emissions. However, the authors also report that:

‘...household-specific factors apparently matter more than fuel choice in determining PM10 concentrations (PM10 is a measure of the concentration of tiny particles in the air smaller than ten microns that can damage the lungs.) In some biomass-burning households, concentrations are scarcely higher than in households that use natural gas. Our results suggest that such variation between households is strongly affected by structural arrangements: cooking locations, construction materials, and ventilation practice ... poor families may not have to wait for clean fuels or clean stoves to enjoy significantly cleaner air. Within our sample household population, some arrangements are already producing relatively clean conditions, even when ‘dirty’ biomass fuels are used. Since these arrangements are already within the means of poor families, the scope for cost-effective improvements may be larger than is commonly believed’. (Dasgupta et al, 2004).

[top] [end]Kitchen ventilation study

In this study 20 briquettes of charcoal were burned in an approximately 15 cubic metre test kitchen building with a measured air exchange rate of approximately 3 air exchanges per hour when closed. Testing was only done on calm days. Charcoal was used instead of wood because it burns consistently without tending, reducing variability in the concentration of pollution introduced to the building. The emissions monitoring equipment consisted of 6 HOBO carbon monoxide monitors and one Airmetrics Minivol pump and filter particulate meter, drawing room air at 5 litres per minute though a filter collecting particles 2.5 microns in size or smaller (PM2.5).

Three tests were performed for each configuration:

1). All windows and doors closed, 2.) One 0.6 m by 1.8 m door open, 3.) One 20 cm by 25cm hole in the roof, 4.) Opening a small 28 cm by 36 cm window along with the 20 cm by 25cm hole in the roof.

The kitchen diagram (Figure 1) shows the size and location of openings as well as the placement of monitoring equipment.

The charcoal was left to burn vigorously for 30 minutes. It was then quickly removed through a small opening, which was then closed. The test continued for another 30 minutes as levels of carbon monoxide and particulate matter declined. Measurement was started at the time the fire was lit, and continued for a total of one hour.
Figure 1: Diagram of test kitchen for ventilation study
Figure 1: Diagram of test kitchen for ventilation study

[top] [end]Results

Figure 2 shows both the peak concentration of carbon monoxide reached after the half-hour of burning, the average level throughout the test, and the average concentration of particulate matter during the four levels of ventilation from the room being completely closed. Increasing amounts of ventilation significantly lowered levels of both types of emissions.
Figure 2: CO and PM2.5 concentrations in the test kitchen; the effects of differing ventilation
Figure 2: CO and PM2.5 concentrations in the test kitchen; the effects of differing ventilation


Figure 3 shows the average CO concentration at the height of 1.4 m above the floor for the duration of each test: Each configuration was tested three times with a constant pollution source.
Figure 3: Average CO concentrations at 1.4m height
Figure 3: Average CO concentrations at 1.4m height
Table 1 summarizes the variability and potential reduction in IAP resulting from the four configurations:
Table 1: CO and average PM reduction caused by ventilation
Table 1: CO and average PM reduction caused by ventilation
Levels of both CO and PM2.5 doors and windows closed were highly elevated, as can be expected. Opening the door was highly effective in this study, reducing pollution levels by 96%. Opening a small hole in the roof also appears to significantly improve air quality. imultaneously opening a small window did little to reduce levels of pollution, possibly because it did not add much flow to the movement of CO and particles through the smoke hole in the roof.

[top] [end]Stratification of CO and PM2.5 in the test kitchen

Three additional tests were run to study stratification in the closed kitchen using 6 HOBO CO data loggers and 6 MiniVol PM monitors at three different heights on opposite sides of the room. The HOBOs and MiniVols were located across from each other at 1 meter, 1.4 meters, and 1.8 meters in height. Some horizontal stratification was observed. It was apparent that both the CO and PM2.5 tended to collect in higher concentrations near the ceiling and to taper off to lower levels near the floor.
Figure 4: Stratification of CO and PM2.5 by height in an unventilated test kitchen
Figure 4: Stratification of CO and PM2.5 by height in an unventilated test kitchen

[top] [end]Conclusion

Inhaling even small amounts of particulates can lead to increased mortality. A national study in the U.S. concluded that there is a 0.5 percent increase in the relative rate of death from all causes for each increase in the PM10 level of 10 micro gram /m3. The estimated increase in the relative rate of death from cardiovascular and respiratory causes was 0.68 percent for each increase in the PM10 level of 10 micro gram /m3 (Samet 2000). The very high levels often found in houses using biomass for heating and cooking are therefore of major concern.

More than 30 stoves have been tested for emissions in the Aprovecho test kitchen. In the unventilated (3 air exchanges per hour) test kitchen when burning five different fuels, levels of PM2.5 were between 50 and 25,000 micro gram/m3.

An effective strategy for decreasing indoor air pollution in houses using charcoal (which may also be valid for other solid fuel burning stoves), seems to be increasing the ventilation. Some of the interventions tested which increased ventilation resulted in a reduction of both carbon monoxide and particulate matter. Opening the door was especially effective. Opening a small hole in the roof seemed to assist the removal of the smoke from the kitchen as it rose up to the ceiling. Other successful methods of ventilation include opening spaces in the eaves and using the stove under a simple smoke hood built within the home.

In the Bangladesh study, ventilation factors also accounted for large differences in PM10 concentrations across households. Unvented smoky fires used inside houses will create dangerous conditions injurious to health. Merely increasing the amount of ventilation will not solve this problem. However, increased ventilation may be a partial remedy that was found in this laboratory study to be effective in reducing levels of CO and PM2.5.

Both carbon monoxide and particulate matter seem to stratify by height in a kitchen, collecting densely at the ceiling and decreasing gradually towards the floor. Levels were lowest near the floor suggesting that exposure could also be reduced by remaining seated or by squatting while cooking.

This study was funded by a grant from the Shell Foundation supporting the development of an accurate, inexpensive method for monitoring indoor air pollution.

[top] [end]References

  1. Naeher L, Smith KR, Brauer M, Chowdhury Z, Simpson C, Koenig J, Lipsett, Zelikoff J, Critical Review of the Health Effects of Woodsmoke, 2005.
  2. Dasgupta S, Huq M, Khaliquzzaman M, Pandey K, Wheeler D. Indoor Air Quality for Poor Families: New Evidence from Bangladesh, World Bank Policy Research Working Paper 3393, September 2004.
  3. Samet J, Dominici F, Curriero F, Coursac I, Zeger S. Fine Particulate Air Pollution and Mortality in 20 U.S. Cities, 1987–1994N Engl J Med. 2000 Dec 14;343(24):1742–9).

[top] [end]Download the original article

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[top] [end]Contents: Boiling Point 52 - Health, safety and household energy

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Theme editorial: Household energy for life - Update on the health and climate impacts of household solid fuels - Spreading innovative biomass stove technologies through China and beyond - Pollution factors affecting health and safety in rural Zimbabwe - Protecting children from indoor air pollution exposure through outdoor cooking in rural South Africa - Direct contact hazards of cookstoves - Burns, cuts, and scalds - Introducing alcohol stoves to refugee communities - GTZ News BP52 - Household energy, indoor air pollution and health at the 14th session - The effect of ventilation on carbon monoxide and particulate levels in a test kitchen - Methanol stoves for indoor air pollution reduction in Delta State Nigeria - Solar cooking and health - Fuel briquettes from wastes - Charcoal making from agricultural residues - What's happening in household energy BP52? – Energy News From Practical Action BP52





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