Gas ovens pollute homes with high levels of nitrogen dioxide

Nitrogen dioxide (NO2) levels inside people’s homes could be higher than outside in the street – with 25% of homes exceeding World Health Organisation recommended safety levels, and it’s all thanks to gas ovens and unventilated gas heaters, says new research into indoor air quality.

Gary Raw, Director of the Centre for Safety, Health and Environment at the Building Research Establishment (BRE), whose new research into indoor air quality in the modern home is due to be published shortly, has found particularly high levels of NO2 in kitchens. Gas ovens tend to double the level of NO2 in the kitchen, although cooking on top of a gas cooker has nowhere near such a marked effect, he says.

According to Raw, it is not known exactly what is causing the higher levels of NO2 from ovens. It could be that the ovens themselves produce more NO2, or that people using the gas rings on top of the cooker tend to ventilate the room more effectively, such as with an extractor fan. However, in order to be fully effective, extractor fans have to be capable of turning over the total air in the room in a matter of minutes, says John Hoskins, an independent health and safety consultant.

One of the dangers of NO2 pollution in the home is that residents are unaware of the gas’ presence, even in relatively high concentrations, says Hoskins. The gas goes deep into the lungs, and as it is not an irritant its inhalation does not result in coughing, and so does not alert residents of its presence.

Other indoor pollutants include carbon monoxide, which is also increased with the use of a gas oven; and formaldehyde, which is emitted by building and decorating materials such as flooring and insulation and has the highest levels in new homes. Total volatile organic compounds (TVOC) are also higher in new homes, and tend to be highest where decorating materials such as paints are stored within the home, including in an attached garage.

However, other than with NO2, there is little to be concerned about. “Just because we can measure them doesn’t mean we have to worry about them,” said Hoskins.

The most important way in which to control indoor air quality is in reducing emissions at source, says Raw. Improved ventilation systems should not be relied on, because they depend on the operator’s ability, knowledge and inclination to use them.

However, says Dr Joe Watson of the Gas Analysis and Sensing Group (GASG), based at the University of Wales, Swansea, whereas in the US new houses come with effective ventilation systems as standard, in the UK what is provided – such as trickle ventilators and chimneys – is ineffective and easy to be unknowingly blocked up by residents. Air quality in an incorrectly ventilated bedroom first thing in the morning in the UK is often so bad that if it were a work place it would be shut down, claims Watson, calling for new homes to have systems such as passive stack ventilation (PSV) installed.

Nevertheless, the most significant source of NO2 pollution is still vehicle congestion in cities, says Hoskins, with heavy-duty lorries being by far the worst offenders, producing 20 times as much of the gas as cars and vans.

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