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The Truth About Diesel Emissions
Diesel Engine Exhaust Emissions
Diesel engine exhaust emissions have the potential to cause a range of health problems. This is a short guide for employees to the hazards posed by the emissions, and describes the precautions that employers and individuals
can take.
WHAT ARE DIESEL ENGINE EXHAUST EMISSIONS?
Diesel engine exhaust emissions (commonly known as 'diesel fumes') are a mixture of gases, vapours, liquid aerosols and substances made up of particles. They contain the products of combustion including:
• carbon (soot);
• nitrogen;
• water;
• carbon monoxide;
• aldehydes;
• nitrogen dioxide;
• sulphur dioxide;
• polycyclic aromatic hydrocarbons.
The carbon particle or soot content varies from 60% to 80% depending on the fuel used and the type of engine. Most of the contaminants are adsorbed onto the soot. Petrol engines produce more carbon monoxide but much less soot than diesel engines.
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WHAT FACTORS AFFECT THE COMPOSITION OF DIESEL FUMES?
The quantity and composition of diesel fumes in your workplace may vary depending on:
• the quality of diesel fuel used;
• the type of engine, eg standard, turbo or injector;
• the state of engine tuning;
• the fuel pump setting;
• the workload demand on the engine;
• the engine temperature;
• whether the engine has been regularly maintained.
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WHAT DOES THE COLOUR OF THE SMOKE PRODUCED INDICATE?
Smoke is the product of combustion. Vehicles at your workplace may produce three kinds of smoke, two of which indicate engine problems. The three types are:
• blue smoke (mainly oil and unburnt fuel) which indicates a poorly serviced and/or tuned engine;
• black smoke (soot, oil and unburnt fuel) which
• indicates a mechanical fault with the engine;
• white smoke (water droplets and unburnt fuel) which is produced when the engine is started from cold and disappears when the engine warms up.
With older engines, the white smoke produced has a sharp smell which may cause irritation to your upper respiratory system.
You should tell your employer if workplace vehicles are producing blue or black smoke so that prompt action can be taken to correct any problem.
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WHERE ARE DIESEL FUMES LIKELY TO BE FOUND IN THE WORKPLACE?
You may be exposed to diesel fumes if you work where diesel operated heavy vehicles are being used, or where motor vehicles are generating diesel fumes such as when coming into and out of car parks or when passing toll booths.
You may also be exposed to diesel fumes if you are working in tunnels or on construction sites where diesel operated stationary power sources are being used.
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DIESEL FUMES AND YOUR HEALTH
Breathing in diesel fumes can affect your health, and exposure to the fumes can cause irritation of your eyes or respiratory tract. These effects are generally short term and should disappear when you are away from the source of exposure.
However, prolonged exposure to diesel fumes, in particular to any blue or black smoke, could lead to coughing, chestiness and breathlessness.
In the long term, there is some evidence that repeated exposure to diesel fumes over a period of about 20 years may increase the risk of lung cancer. Exposure to petrol engine exhaust emissions does not have the same risk.
Skin contact with cold diesel fuel may cause dermatitis.
If you think that your health is being affected by exposure to diesel fumes, you should tell your employer (eg supervisor) and/or safety representative, and consult your doctor.
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WHAT SHOULD MY EMPLOYER DO TO PROTECT MY HEALTH?
Under the Control of Substances Hazardous to Health Regulations 1994 (COSHH), your employer should make a suitable and sufficient assessment of the risks to your health if you are exposed to diesel fumes. They should then take the necessary steps to prevent or adequately control your exposure in the workplace.
Where exposure cannot be prevented, your employer will need to consider the use of a combination of specific control measures including:
• workplace air extraction fans;
• tailpipe exhaust extraction systems;
• the use of filters attached to tailpipes;
• catalytic converters; and more general control measures such as:
• turning off engines when not required;
• keeping doors and windows open where practicable;
• installing air vents in the walls and ceiling;
• job rotation;
• providing suitable personal protective equipment (suitable gloves should be worn when handling hot and cold diesel fuel).
Your employer should only provide respiratory protective equipment as a last resort when other means of control are not suitable.
The presence of soot on the walls or on other surfaces in your workplace is a useful indicator that diesel fumes are not being adequately controlled.
In addition to the control measures described in the preceding paragraphs, your employer should also ensure that:
• any engineering controls used are properly maintained and checked regularly;
• where necessary, your exposure to diesel fumes is monitored (see HSG publication Control of diesel engine exhaust emissions in the workplace - full details at end of text);
• you are provided with the necessary information on the risks of exposure to diesel fumes;
• you are provided with instruction and training on the safe use of the control measures and any personal protective equipment that you are using.
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WHAT CAN I DO TO PROTECT MY OWN HEALTH?
You can do a number of things to protect your health from exposure to diesel fumes. These include:
• ask your employer for information on the hazards associated with diesel fumes, read it, make sure you understand it and if not, seek clarification;
• avoid exposure where possible;
• make full use of any controls provided;
• know how to use the controls provided and be able to detect any faults;
• report any faults in the controls to your employer, eg poor extraction fans;
• keep doors and windows open to remove any iesel fumes where possible;
• turn off engines when not required;
• know how to correctly wear any respiratory protective equipment or personal protective equipment your employer provides;
• keep it clean and serviced, and store in a clean area provided by your employer.
In addition to these controls, there are a number of personal hygiene measures you can take:
• do not eat or smoke in areas where there is likelyto be exposure;
• wash your hands and face before drinking, eating or leaving work;
• avoid skin contact with cold diesel fuel and hot fuel or oil.
Remember, you have a duty not only to protect your own health and safety but also to ensure that your actions do not put others around you at risk.
The Truth
Forget about all those smoky old buses and trucks, the truth is that the modern diesel car is as clean, and probably cleaner than an equivalent petrol car. Don't believe me? Read on.
The five main emissions for petrol and diesel cars are:
Carbon Dioxide (CO2)
Carbon Monoxide (CO)
Nitrogen Oxides (NOx)
Hydrocarbons
Particulates
Of these five, a diesel car is better than a petrol car with three of them, about the same with one, and worse with one. Only one of these classes of emissions is visible (particulates, or soot), and rather unfortunately for diesel cars, that is the one which is worse for them. The three emissions for which petrol cars are worse are invisible, so you won't realise that they are there; however they still cause harm to health and the environment.
What problems do these emissions cause, and how does diesel stack up:
Carbon Dioxide
Carbon dioxide is the main cause for concern at the moment, and is the subject of international agreements to try to reduce its output. Carbon dioxide is causing global warming; this is a known fact. Carbon dioxide is produced by any burning of fossil fuels, and is caused by production of electricity by most current powerstations; this means that electric cars cause carbon dioxide emissions too. Carbon dioxide does not cause any health issues.
Carbon dioxide emissions are directly proportional to fuel consumption, and as diesel cars use 30 to 40% less fuel, they emit 30 to 40% less carbon dioxide than petrol cars.
Natural gas and LPG cars are actually quite fuel inefficient, if otherwise cleaner burning, and so produce more CO2 than a diesel.
Although CO2 emissions are not directly harmful to us, they are changing our climate. The legacy these emissions will leave will be felt by every generation after us.
Carbon Monoxide
Carbon monoxide is a poison. It has no smell, but can kill you without you realising what is happening. Carbon monoxide is the reason why you should not run you car engine (petrol) in a confined space.
Diesel engines produce virtually no carbon monoxide, a petrol engine produces enough to kill you. The main remedy to carbon monoxide emissions of petrol engines has been the introduction of catalytic converters, however there are problems with cats:
hey don't work until they are hot, maybe 10 or 15 minutes of driving. As most car journeys only last 10 or 15 minutes, the cat is not terribly effective. They increase fuel consumption. They are easily poisoned and stop working.
They are easily mechanically damaged.
Nitrogen Oxides
Nitrogen is the main constituent of the air that we breathe. When it is exposed to high pressures and temperatures it combines with oxygen in the air to form nitrous oxides. The nitrous oxides then combine with low level ozone to form smog.
Because of the way a diesel engine works, with an excess of air inside the engine (rather than "just enough" as in a petrol engine, which is what causes CO emissions), nitrous oxides are more likely to be formed.
However tests of actual cars reveal that whilst emissions of NOx are higher in a new diesel than a new petrol car, that by 50,000 miles or so they are the same, and after that the petrol engine produces more than the diesel. Therefore over the life cycle of the car, petrol and diesel engine emissions of nitrous oxides are similar.
Emissions of nitrous oxides can be effectively reduced in both petrol and diesel cars by use of exhaust gas recirculation (EGR). EGR reduces the combustion temperature to below the point where nitrogen effectively burns.
Hydrocarbons
Hydrocarbons include chemicals such as benzene. Benzene is an extremely carcinogen chemical, and has been declared unsafe by the World Health Organisation in any concentration. Hydrocarbon emissions are contained in petrol engine emissions much more than in diesel engine emissions. Benzene is also present in the fumes which can be smelt when filling up with petrol at a service station, this is not a problem with diesel.
Particulates
Particulates or smoke are really the only problem for diesels (compared with petrol engines). Most of the controversies and newspaper scare stories center around particulates. Various groups have been trying for years to prove a link between diesel smoke and cancer, and so far have failed to actually prove anything.
Friends of the Earth may come up with statements such as "Small particles are believed to lead to 8,100 premature urban deaths every year (1.9% of all deaths in urban areas)" and then apply them to diesel emissions, but this is flawed because:
The studies were carried out in American cities where the penetration of diesel in the market is lower. Any increase in deaths due to particulates, if it exists, may be caused be particulates from some other source; the particulates in question have not been indisputably linked with diesel emissions.
Even in Europe, particulates from diesel cars are a very small percentage of the particulate emissions which we breathe; most are from industry.
Diesel engines emit more PM10 particles, that is particles which have a diameter up to 10 microns, but petrol cars actually emit more PM1 particles than diesel ones. These particles are smaller than 1 micron and are invisible. They are also more likely to penetrate deeply into human lungs (as they are smaller) and look less like a natural dust particle, which human lungs have evolved to cope with.
Even if particulates are a factor in the deaths of 8,100 people every year in the UK, then these are the most seriously unwell people in the country. The fact is that we are talking about 8,100 people who are about to die, with or without particulates around.
The original research which led to the link between deaths and particulates is being questioned. See Merlise Clyde's paper, Model Uncertainty and Health Effect Studies for Particulate Matter, which can be downloaded from THE NATIONAL RESEARCH CENTER FOR STATISTICS AND THE ENVIRONMENT in Washington.
Summary
Diesel cars are better than petrol cars with reference to carbon dioxide, the global warming gas.
Diesel cars are better than petrol cars with reference to carbon monoxide, a poison.
Diesel cars are better than petrol cars with reference to hydrocarbons which cause cancer.
Diesel cars are similar to petrol cars with reference to nitrous oxides, which cause smog.
Diesel cars are worse than petrol cars with reference to particulates, which have unproved health impacts
Health Effects Of Diesel Emissions
Diesel exhaust contains several pollutants that can be harmful to public health alone or in combination with other substances. These include hydrocarbons, nitrogen oxides, fine particulate matter, carbon monoxide, and toxic air contaminants known as hazardous air pollutants.
• Nitrogen oxides (NOx) are by-products of fuel combustion and contribute to the formation of ground-level ozone or "smog." Health effects include coughing, shortness of breath, and decreased lung function.
• Fine particulate matter (PM2.5) is the term used for the mixture of solid particles and liquid droplets in the air. Because of its small size, fine particulate matter can be deposited deep in the lungs, where it can cause health problems. Nitrogen oxides and sulfur dioxides are also major sources of fine particulate matter.
Recent studies have shown an association between particulate matter and premature mortality from respiratory and cardiovascular disease, and increased incidence of respiratory illness, particularly in children and the elderly. For adults with heart or lung conditions, exposure to fine particulate matter can cause more illness and in some cases premature death. More than 90 percent of the particulates found in diesel exhaust are fine particles.
• Hydrocarbons (HC) are formed by incomplete fuel combustion. When combined with NOx in the presence of sunlight, HC's produce ground-level ozone or "smog," which can irritate eyes, damage lungs, and aggravate respiratory problems. Symptoms include coughing, shortness of breath, and decreased lung function. Many hydrocarbons are also considered hazardous air pollutants.
• Carbon monoxide (CO) is formed by incomplete fuel combustion. Carbon monoxide reduces the flow of oxygen in the bloodstream and is of particular concern to people with heart disease.
• Hazardous Air Pollutants (HAPs) Diesel exhaust contains 40 substances that the U.S. Environmental Protection Agency lists as hazardous air pollutants-15 of these are considered probable or known human carcinogens. Of greatest concern are
Environmental Effects
Nitrogen oxides contribute to acid rain and to the acidification of lakes and soils. They can also affect aquatic ecosystems by providing too many nutrients to aquatic plant life, which reduces dissolved oxygen levels and can ultimately harm the ecosystem. In addition, nitrogen oxides and hydrocarbons contribute to the formation of ground-level ozone or "smog," which is highly corrosive and damages crops and forests.
Particulate matter is a major cause of poor visibility and haze in many parts of the United States. Air pollution, largely due to particulate matter, has reduced visibility in some areas from 90 miles to only 14 to 24 miles. Visibility has been affected in urban centers, and in scenic rural areas as well. Fine particulate matter can remain suspended in the air for days and travel long distances
DIESEL EXHAUST PARTICLES AND ITS HEALTH EFFECTS
The popularity of the diesel engine in heavy duty applications in trucking, rail road, marine transport, DG sets and construction industry is due to both its fuel efficiency and long service life relative to the gasoline engine.
Compared with gasoline engine, diesel emissions are lower in carbon monoxide (CO), hydrocarbon (HC) and carbon dioxide (CO 2 ), but higher in oxides of nitrogen (NOx) and particulate matter (PM).
Diesel exhaust is a complex mixture of both particulate and gaseous phase. Diesel exhaust has particulate with mass median diameter of 0.05 to 1.00 micrometer, a size rendering them easily respirable and capable of depositing in the airways and alveoli.
The particles consist of a carbonaceous core with a large surface area to which various hydrocarbons are absorbed, including carcinogenic polycyclic aromatic hydrocarbons (PAHs) and Nitro-PAHs that have elicited the most concern with respect to human health.
The gaseous phase contains various products of combustion and hydrocarbons including some of the PAHs present in the particle phase. Once emitted, components of diesel exhaust undergo atmospheric transformation in ways that may be relevant to human health.
For example, nitro-PAHs, created by the reaction of directly emitted PAHs with hydroxyl radicals in the atmosphere can be more potent mutagens and carcinogens and more bioavailable than their precursors.
A study undertaken by a Swedish Consultancy, Ecotraffic (Peter Ahlvik and Ake Branberg,1999) shows that the cancer potency of diesel vehicles is more than two times than that of petrol vehicles in India (Fig 12).
But if only the most harmful of the exhaust emissions, that is particulate emission is considered, the carcinogenic effect of one new diesel car is equivalent to 24 petrol cars and 84 new CNG cars on the road. The Honorable Supreme Court of India has restricted the use of commercial diesel driven vehicles in Delhi due to its harmful effects.
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