Hi Simon, The exhaust gases will be hot instantly and the exhaust system will heat up pretty quickly, engine temperature will have no bearing whatsoever.

Even very low levels of CO can have health effects....and while the manufacturers say that levels are "nil" "very low" , I have yet to find one that will stay in a closed room with a running LPG lift truck. The effect is: "Carbon monoxide has 210 times greater affinity for haemoglobin than oxygen. A small environmental concentration will thus cause toxic levels of carboxyhaemoglobin. After the carbon monoxide has selectively bound to haemoglobin the oxygen-haemoglobin dissociation curve of the remaining oxyhaemoglobin shifts to the left, reducing oxygen release . The affinity of carbon monoxide for myoglobin is even greater than for haemoglobin. Binding to cardiac myoglobin causes myocardial depression, hypotension and arrhythmias. Cardiac decompensation results in further tissue hypoxia and is ultimately the cause of death." Once CO attaches to haemoglobin, it will no longer carry oxygen. Ever. "Certain people in your household may be affected by carbon monoxide poisoning more quickly than others. Those at particular risk include: babies and young children pregnant women people with heart or breathing problems" http://www.nhs.uk/Condit...ning/Pages/Symptoms.aspx As someone who has been affected by CO poisoning in the past, I would like to point-out that many affected people take considerable time to recover..... Theoretical figures on catalytic converters effectiveness versus possible death or illness. Your choice.