Study exposes hidden dangers of indoor fireplaces on air quality in South African homes

A recent study published in the journal Energy Research & Social Science examines the level of exposure to particulate matter (PM) in two types of indoor fireplaces and their association with outdoor temperatures.

Study: Lifting the unseen smokescreen on indoor air quality due to amenity indoor fireplaces in South African homes. Image Credit: thala bhula / Shutterstock.com

The health effects of household air pollution

The World Health Organization (WHO) defines prolonged exposure to PM 2.5 micrometers (µm) in size or less (PM_2.5) at levels over 15 µg/m³ for more than three days each year as being detrimental to health and development.

Within Africa, the domestic burning of wood, coal, and gas for cooking or heating is the main contributor to ambient PM. In fact, up to 34% and 20% of ambient PM_2.5 air pollution can be attributed to domestic fuel burning in Africa and worldwide, respectively.

Household air pollution (HAP) is a major cause of illness worldwide, as exposure increases the risk of diabetes, cancer, acute respiratory infections, strokes, cardiovascular disease, low birth weight, and death due to cardiovascular and respiratory diseases.

In 2019 alone, HAP exposure is estimated to have contributed to over 2.3 million deaths, which comprised 4% of all deaths. In South Africa, 5,590 deaths were directly attributed to HAP from cooking fuel use.

Fuel sources in South Africa

HAP from fuel burning varies with the fuel type. The “energy ladder” theory indicates that households transition from traditional to cleaner fuels as they can afford it. In contrast, the “energy stacking” hypothesis suggests that cost is only one factor, as availability and social acceptability also contribute to the selection of fuel sources.

The energy stacking theory reflects the reality of fuel use patterns in South Africa, where even affluent households use both electricity and traditional fuels.

Indoor fireplaces are often installed to provide a sense of comfort and security during winter months, especially in homes with inadequate insulation. Enclosed fireplaces, an alternative to open fireplaces, burn fuel slowly and are widely believed to emit less pollution.

About the study

Researchers in the current study mapped indoor air quality in terms of PM_2.5 in six wealthy homes where indoor burning of fuel is not a necessity but a choice.

PM_2.5 levels were measured 130 times daily between May and September, reflecting the coldest months in the southern hemisphere. These measurements were obtained with at least one laser-scattering PM sensing device placed inside the home.

PM_2.5 measurements were correlated with weather conditions at the time to determine the impact of ambient conditions on indoor environmental settings. Four homes had open fireplaces, while two had enclosed fireplaces, which enabled a direct comparison of the health effects of both fireplaces.

What did the study show?

For all houses, PM_2.5 levels exceeded 10 µg/m³ in at least one quartile. Furthermore, 24-hour average PM_2.5 concentrations also frequently exceeded WHO 24-hour guidelines of 15 µg/m³.

PM_2.5 peaks were defined as when PM_2.5 levels exceeded 60 µg/m³. The average duration of each peak was between 52 and 210 minutes, with the time needed to return to threshold levels ranging from 42 to 190 minutes.  

Importantly, many of these measurements were obtained throughout the day, even when the fireplace was not actively being used. When fireplace use levels were considered, exposure to PM_2.5 was particularly high, as 75% of sample measurements in all houses exceeded 100 µg/m³, with median values between 82-103 µg/m³.

PM_2.5 levels also correlated with ambient weather conditions in a negative linear manner. Thus, colder outdoor temperatures may lead to fireplaces being used more frequently or more intensively.

Average peaks with PM_2.5 levels above 60 µg/m³ were not significantly raised with open fireplaces compared to enclosed fireplaces. However, this observation was based on only two of the six households and cannot be considered conclusive.

Conclusions

Average measurements when the fireplace was in use indicate that PM_2.5 levels exceeded dangerous thresholds. The risk of exposure was higher during cold weather; however, no significant difference was observed between open and closed fireplaces.

The potential behavioral benefit of sharing this information with households was observed with one family, as indoor fireplace use was immediately stopped, which subsequently led to a significant decline in PM_2.5 levels.

Future studies are needed to confirm the observed trends in broader regions and more diverse populations. They should examine the type and amount of wood used, as well as the period of fireplace use. Educational and awareness interventions, such as providing households with the option to see their indoor air quality (IAQ) data, must also be explored.