Under The Microscope: A Fatal Doze

 

After alcohol and some pharmaceutical drugs, carbon monoxide poisoning is probably the most common toxic condition to be met with in routine forensic pathology. The widespread introduction of natural gas (which contains no carbon monoxide) as a replacement for 'coal gas' as a heating fuel has removed a major source of the poison. Monoxide still provides lethal dangers in many other ways, however. It is produced whenever fossil fuels are incompletely oxidized to carbon dioxide and, because of its great affinity for haemoglobin, even low concentrations can be cumulative. There are a vast number of publications on carbon monoxide toxicity, both in an environmental and industrial context. Once again, this discussion is confined to the pathologist's involvement in fatalities. A body coming to autopsy with suspected (or sometimes unsuspected) carbon monoxide poisoning, will have suffered that toxic condition by the following means. Since the replacement of coal gas (containing up to 7 per cent monoxide) with natural gas, a major means of suicide has been removed. 'Putting the head in the gas oven' was the most common form of self-destruction in Britain and many other countries until this changeover. Since then, suicides have obtained carbon monoxide to kill themselves from the internal combustion engine.

Diesels produce far less monoxide than petrol engines. Normally, the exhaust pipe vents the gases into the atmosphere, where it may contribute to considerable low-level monoxide contamination in large cities, such that policemen on traffic duty may have up to 10 per cent saturation of their haemoglobin. When the exhaust fumes are confined to a small space, then a dangerous or lethal level can build up in a short space of time. It is calculated that a 1.5 litre petrol engine, idling in a closed single garage, can produce a lethal concentration in the atmosphere within 10 minutes.

Some suicides will merely sit in the garaged car with a window open and allow the gas to overtake them. More commonly, some device is fitted to pipe the gas into the interior of the car and this may be done outside a garage, often in a remote parking spot. The flexible tube from a vacuum cleaner seems a favourite means, though ordinary hose-pipe, pushed inside the tail-pipe and led in through a window, is a common alternative. Apart from suicide, accidental poisoning sometimes occurs in relation to internal combustion engines. A mechanic or car owner may work on a vehicle in a closed garage, especially in cold weather, and be overcome by monoxide before he is able to remove himself from the danger. The insidious nature of the toxic effects may make him unaware of the supervening stupor and coma.

Carbon monoxide can also affect drivers of a moving vehicle, usually because of a defective exhaust system, which allows gas to percolate through the floor or engine bulkhead into the interior. Rarely, a strong following wind blows the external exhaust gas into the open doors of a van or truck. Another motoring cause is a leak in the heat exchanger in those vehicles that use a direct air supply from around the exhaust manifold to provide passenger heating.

In aircraft - usually light planes with the engine immediately adjacent to the cockpit - a leakage of exhaust gas from the motor compartment can lead to disablement of the pilot and death from a crash rather than from fatal toxicity. The same applies to those road-vehicle drivers who are overcome by the gas to an extent that makes them incapable of driving safely.

The differential diagnosis in survivors is between carbon monoxide and alcohol, as the clinical symptoms of both are quite similar at one stage of the toxic process. Deaths have also been reported in 'scuba' divers, whose air cylinders have been contaminated with carbon monoxide during refilling from faulty petrol-driven compressors.

 

Domestic heating appliances can produce carbon monoxide in addition to the usual dioxide from a restriction of their air supply, so that incomplete combustion of the fuel takes place. The fuel can be natural gas, which, though itself free from monoxide, is only partially oxidized from some defect of design, maintenance, or patency of the exhaust flue. Solid-fuel boilers used for central heating may have some restriction of air entry or a partial blockage of the chimney system. Paraffin (kerosene) heaters may burn with inadequate oxygen ingress and any other form of hydrocarbon fuel appliance can malfunction so that part of the products of combustion are monoxide.

Gas appliances, especially water heaters, are one reason why the bathroom is such a dangerous place. Apart from the extra hazards of electricity, a bath for drowning, wet surfaces for slipping, tablets in the cabinet and sharp instruments such as razor blades, the small-sized room and the frequent installation of a gas water heater or 'geyser' makes this room a frequent locus for unnatural death. Blockage of the exit or 'flue' pipe is a common fault, sometimes from bad installation or because it becomes blocked by soot or by birds' nests.

A common cause of monoxide deaths arises from structural fires in houses and other buildings. As described in Chapter 11, the majority of deaths in house conflagrations are caused not by burns, but by inhalation of smoke. These fatalities are largely caused by carbon monoxide poisoning, though other lethal gases such as cyanide, phosgene and acrolein are partly responsible. Many victims of house fires die remote from the flames, and may be overcome in different rooms or even on different floors, the monoxide percolating considerable distances and killing persons either asleep or trapped elsewhere in the building.

 

Acknowledgements:

www.aived.nl    AIVD – @Erik Akerboom ©

www.politie.nl  Politiekorpschef  @Janny Knol©

www.politie.nl WEB Politie - @Henk van Essen©

 

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