Pollutants from gas cookers

For thousands of years wood was the only fuel used by us. However, when we discovered that fossil fuels _ coal, oil and natural gas _ could generate more heat than wood, we said goodbye to a halcyon period when the air was relatively pure.

 Today, cooking stoves, water heaters, outdoor grills, as well as clothes washers and dryers in many homes use natural gas. But seldom do we realise that combustion of natural gas produces health-damaging pollutants like carbon monoxide (CO) and nitrogen dioxide (NO2), including soot that penetrates deep into our lungs. 
All gas-fired cookers and ovens produce CO, but that does not mean they have to be dangerous. However, studies show that about half of all stoves raise concentrations of CO in the kitchen beyond the established safe level of nine parts per million (ppm). 
Gas flames in a stove are normally blue, but sometimes they burn yellow or red. If you see yellow or red flame, it is a sign of incomplete combustion, wasting gas and generating dangerous levels of CO and NO2. A blue flame, on the other hand, indicates complete combustion, meaning gas is not wasted. It also minimises the production of CO and NO2. 
In an unvented kitchen with closed windows, levels of pollutants produced by gas stoves can increase from a few ppm to over 40 ppm, when four burners are in use for half an hour or so. Carbon monoxide levels also increase appreciably in neighbouring rooms.  Nitrogen dioxide levels often follow the same pattern. Dubbed as the ‘silent killer’, CO is a colourless, tasteless and odourless gas. Poisoning due to CO is difficult to detect because the symptoms are identical to that of flu.
Of course, concentrations of indoor air pollutants fall after combustion sources are turned off, but it may take several hours before normal levels are reached in conventional, poorly sealed homes. In well-sealed energy efficient homes with inadequate ventilation, it can take much longer. If several lengthy meals are cooked during a day, as in most Bangladeshi homes, exposure to these pollutants can be quite high.
Human health is affected in many different ways from exposure to pollutants originating from stoves. Among the primary ones are cardiac, vascular and neurological impairments. Infants, children, elderly people and pregnant women are most vulnerable to the effects of indoor pollution. Millions of people die prematurely every year from illness attributable to indoor air pollution.
How does CO cause poisoning? When CO is inhaled, the bloodstream carrying oxygen throughout the body absorbs the gas. When this CO is carried to components of the body expecting oxygen, the chemistry is wrong.     The health effects of CO depend on the concentration and length of exposure, as well as a person’s health condition. Most people will not experience any symptoms from prolonged exposure to CO levels of approximately 1 to 70 ppm, but some heart patients might experience an increase in chest pain. As CO levels increase and remain above 70 ppm, symptoms become more noticeable and can include headache, fatigue and nausea. At sustained CO concentrations above 150 to 200 ppm, disorientation, unconsciousness, and death are possible. The other effects of CO are headaches, reduced mental alertness, heart attack, cardiovascular diseases and impaired fetal development. 
Those inhaling NO2 are susceptible to respiratory infections, irritation of the lung and respiratory symptoms such as cough, chest pain and difficulty in breathing. Other effects include eye and throat irritation, coughing, respiratory tract problems, asthma, lung damage.
How can we minimise pollution from combustion sources? The strategy depends on the source of pollution. To prevent pollution from leaky sources, the best way is to plug up the leaks or replace the appliance. For unvented combustion sources, like stoves, exhaust fans should be used when houses are closed up. On warm days, the windows should be cracked open. If ventilation is impossible, one might want to replace the gas stove with an electric stove, bearing in mind that electric ranges are more inefficient and costly than natural gas or propane. Kerosene stoves should be avoided altogether.
Sustainable strategies, such as passive solar space and water heating, can help reduce indoor combustion by water heaters and reduce ambient air pollution as well. In tightly sealed, energy-efficient homes, air-exchange systems can be installed for use when the house is closed off. These systems periodically replace room air with outside air. Some systems merely bring in new air and vent old air. Others contain heat exchangers that transfer heat to the incoming air, reducing the amount of heat lost to the outside. Certain plants also help reduce indoor air pollution. For example, one spider plant per room is sufficient to prevent the buildup of nitrogen oxide.
Remember, whenever you produce yellow or red flame, you are producing CO. 

The writer is Professor of Physics at Fordham University, New York.

Pollutants from gas cookers

For thousands of years wood was the only fuel used by us. However, when we discovered that fossil fuels _ coal, oil and natural gas _ could generate more heat than wood, we said goodbye to a halcyon period when the air was relatively pure. Today, cooking stoves, water heaters, outdoor grills, as well as clothes washers and dryers in many homes use natural gas. But seldom do we realise that combustion of natural gas produces health-damaging pollutants like carbon monoxide (CO) and nitrogen dioxide (NO2), including soot that penetrates deep into our lungs. All gas-fired cookers and ovens produce CO, but that does not mean they have to be dangerous. However, studies show that about half of all stoves raise concentrations of CO in the kitchen beyond the established safe level of nine parts per million (ppm). Gas flames in a stove are normally blue, but sometimes they burn yellow or red. If you see yellow or red flame, it is a sign of incomplete combustion, wasting gas and generating dangerous levels of CO and NO2. A blue flame, on the other hand, indicates complete combustion, meaning gas is not wasted. It also minimises the production of CO and NO2. In an unvented kitchen with closed windows, levels of pollutants produced by gas stoves can increase from a few ppm to over 40 ppm, when four burners are in use for half an hour or so. Carbon monoxide levels also increase appreciably in neighbouring rooms. Nitrogen dioxide levels often follow the same pattern. Dubbed as the silent killer, CO is a colourless, tasteless and odourless gas. Poisoning due to CO is difficult to detect because the symptoms are identical to that of flu. Of course, concentrations of indoor air pollutants fall after combustion sources are turned off, but it may take several hours before normal levels are reached in conventional, poorly sealed homes. In well-sealed energy efficient homes with inadequate ventilation, it can take much longer. If several lengthy meals are cooked during a day, as in most Bangladeshi homes, exposure to these pollutants can be quite high. Human health is affected in many different ways from exposure to pollutants originating from stoves. Among the primary ones are cardiac, vascular and neurological impairments. Infants, children, elderly people and pregnant women are most vulnerable to the effects of indoor pollution. Millions of people die prematurely every year from illness attributable to indoor air pollution. How does CO cause poisoning? When CO is inhaled, the bloodstream carrying oxygen throughout the body absorbs the gas. When this CO is carried to components of the body expecting oxygen, the chemistry is wrong. The health effects of CO depend on the concentration and length of exposure, as well as a persons health condition. Most people will not experience any symptoms from prolonged exposure to CO levels of approximately 1 to 70 ppm, but some heart patients might experience an increase in chest pain. As CO levels increase and remain above 70 ppm, symptoms become more noticeable and can include headache, fatigue and nausea. At sustained CO concentrations above 150 to 200 ppm, disorientation, unconsciousness, and death are possible. The other effects of CO are headaches, reduced mental alertness, heart attack, cardiovascular diseases and impaired fetal development. Those inhaling NO2 are susceptible to respiratory infections, irritation of the lung and respiratory symptoms such as cough, chest pain and difficulty in breathing. Other effects include eye and throat irritation, coughing, respiratory tract problems, asthma, lung damage. How can we minimise pollution from combustion sources? The strategy depends on the source of pollution. To prevent pollution from leaky sources, the best way is to plug up the leaks or replace the appliance. For unvented combustion sources, like stoves, exhaust fans should be used when houses are closed up. On warm days, the windows should be cracked open. If ventilation is impossible, one might want to replace the gas stove with an electric stove, bearing in mind that electric ranges are more inefficient and costly than natural gas or propane. Kerosene stoves should be avoided altogether. Sustainable strategies, such as passive solar space and water heating, can help reduce indoor combustion by water heaters and reduce ambient air pollution as well. In tightly sealed, energy-efficient homes, air-exchange systems can be installed for use when the house is closed off. These systems periodically replace room air with outside air. Some systems merely bring in new air and vent old air. Others contain heat exchangers that transfer heat to the incoming air, reducing the amount of heat lost to the outside. Certain plants also help reduce indoor air pollution. For example, one spider plant per room is sufficient to prevent the buildup of nitrogen oxide. Remember, whenever you produce yellow or red flame, you are producing CO. The writer is Professor of Physics atFordham University, New York.