Although realistic ketene emission levels may be lower than those reported under the conditions herein, chronic exposure is an additional potential concern, since toxicological data on chronic exposure to ketene is lacking. Moreover, available data on acute exposure to ketene has been described as dated and incomplete. Ketene's most relevant toxicological property is its very high reactivity, as it readily chemically modifies biological molecules. However, ketene does not survive long enough to be detected intact in vivo. Chemical and physical studies such as reported herein and by others are thus required to elucidate sources of exposure.