READERS' LETTERS

Nissara H passed on to me a forwarded email with the subject line "Do not turn on the air-conditioner as soon as you enter the car!" and suggested I investigate.

The forward email reads: "Please open the windows after you enter your car and do not turn on the air-conditioning immediately. According to research, the car's dashboard, seats and air freshener emit benzene, a cancer-causing toxin [or carcinogen - take note of the plastic smell in your car]. In addition to causing cancer, it poisons your bones, causes anaemia and reduces your white blood cell count. Prolonged exposure will cause leukaemia, increase the risk of cancer and may also cause miscarriages.

The acceptable benzene level indoors is 50 milligrammes per square foot. A car parked indoors with the windows closed will contain 400-800mg of benzene. If parked outdoors at a temperature above 15 degrees Celsius, benzene levels go up to 2,000-4,000mg sq ft, 40 times the acceptable level, and people inside the car will inevitably inhale an excess amount of the toxin. It is recommended that you open the windows and door to give time for the interior to air before you enter. Benzene is a toxin that affects your kidney and liver, and is very difficult for your body to metabolise."

Here's my take:

According to the US Environmental Protection Agency (EPA): Benzene is found in the air from emissions from burning coal and oil, petrol stations, and motor vehicle exhausts. Acute (short-term) inhalation exposure of humans to benzene may cause drowsiness, dizziness, headaches, as well as eye, skin and respiratory tract irritation - and, at high levels, unconsciousness. Chronic (long-term) inhalation exposure has caused various disorders in the blood, including reduced numbers of red blood cells and aplastic anaemia. Reproductive effects have been reported for women exposed through inhalation to high levels, and adverse effects on the developing foetus have been observed in animal tests. Increased incidence of leukaemia (cancer of the tissues that form white blood cells) has been observed in humans occupationally exposed to benzene. The EPA has classified benzene as a Group A human carcinogen.

Benzene is used as a constituent in motor fuels; as a solvent for fats, waxes, resins, oils, inks, paints, plastics and rubber; in the extraction of oils from seeds and nuts; and in photogravure printing. It is also used as a chemical intermediate. Benzene is also used in the manufacture of detergents, explosives, pharmaceuticals and dyes.

However, the EPA lists the following sources of potential exposure to Benzene poisoning:

- Individuals employed in industries that manufacture or use benzene may be exposed to the highest levels of benzene.

- Benzene is found in emissions from burning coal and oil, motor vehicle exhaust and evaporation from petrol stations and in industrial solvents. These sources contribute to elevated levels of benzene in the ambient air.

- Tobacco smoke contains benzene and accounts for nearly half the (US) national exposure to benzene.

The EPA does not indicate that the inside of your car is a key source of benzene vapour, but states that the petrol you fuel your car with contains a certain amount of it that you may involuntarily breathe, since it enters the air as it comes out of the exhaust pipe and during refuelling.

The forwarded email is misleading as it suggests that your car's air-conditioning system is the source of the benzene in your car.

The EPA list does not make any reference to benzene levels, but the US and European occupational exposure limit to benzene is 1ppm (part per million), or only 3.25mg per cubic metre of air. The environmental exposure limit to benzene is even less, at 15ppb (parts per billion) or 50mg per cubic metre of air.

Moreover, the European Union (regulation number 793/93) has required all car manufacturers, from 1994, to ensure that the benzene content in a car's interior materials meets the above standards.

As car makers in Thailand also build cars for the export market (including Europe) it is unlikely that this standard is not adopted, as having dual standards for exported and domestic cars or parts would actually cost money.

Older cars made prior to the transfer of technology to conform to the EU regulations might have emitted harmful levels of benzene. However, such emissions should have ceased being released within a few months of manufacture.

Personally, I always take any forwarded emails with a good dose of scepticism as they likely do not come from reliable sources, and never forward them to my friends until, as the Bangkok Post's Database section recommended a long time ago, I check the story out at snopes.com - an excellent website for verifying whether your forwarded email has a grain of truth.

Besides, I think car occupants are more vulnerable to germs built up inside the air-conditioner. That's why I usually turn off the air-conditioning without switching off the fan for at least a minute before shutting down the engine, to reduce the moisture that mould thrives on.

While we're at it, it would be good to replace the air-conditioner's filter (if your car has one) according to the manufacturer's instructions or clean the system's evaporator once a year with a 300 baht tin of DIY cleaning foam - don't fall for the 3,000 baht rip-off at the garage or car detailer.