PHYSICAL AND CHEMICAL PROPERTIES We try to keep CO2 levels in our U.S. Navy submarines no higher than 8,000 parts per million, about 20 time current atmospheric levels. Few adverse effects are observed at even higher levels. – Senate testimony of Dr. William Happer, here CO is a colorless, odorless gas (Budavari et al. 1989). Selected physical and chemical properties are summarized in Table 4-1 . OCCURRENCE CO primarily is produced by partial oxidation of carbon-containing materials (Pierantozzi 1995). In the outdoor environment, major sources of CO are motor vehicles and fires (EPA 2000). In the indoor environment, sources include tobacco smoking, combustion engines, and combustion appliances, such as furnaces and gas stoves. On submarines, the primary sources of CO are tobacco smoking, diesel generators, and high-temperature paints (Crawl 2003). Data collected on nine nuclear-powered ballistic missile submarines indicate an average CO concent...