Older cars tend to produce the highest levels of exhaust carbon monoxide. With the introduction of unleaded petrol in the 80s, there have been controls on the monoxide levels in exhaust gases to meet environmental standards. Since 1997 new cars can emit no more that 10% of the levels of carbon monoxide acceptable in 1976. Mandatory catalytic convertors oxidize most of the produced carbon monoxide to form carbon dioxide.
Despite these significant changes in the emission levels of carbon monoxide, motor vehicle exhaust gas suicides continue to occur at a surprisingly high rate. Indeed, in the period from 1976 to 1995 the rate of exhaust gas suicides in some countries increased faster than the rate of motor vehicle registrations (Routley & Ozanne-Smith, 1998). Possible explanations include the fact that idling motors do not necessarily comply with international standards. Additionally, catalytic convertors do not function when cold. Rather, they require several minutes to warm from a cold start. Of significance though is the increasing number of failed suicide attempts from breathing exhaust gas reported in this period.
This is not to say that the motor car cannot be used as a source of carbon monoxide to effect a reliable death, but there are problems associated with the method. One concern is the mechanical connection of the exhaust to the hose carrying gas to the car. Many modern vehicles have elliptical exhaust outlets. Coupling the exhaust to a round hose, often using plastic tape, can cause problems because of the heat of exhaust gas. If the tape or tube melts or is destroyed by the heat, failure is likely. Fig 6.4 shows a carefully engineered system using metal connections and clamps and heat resistant tubing.