Blood alcohol limit: the CMA is right on
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* James G. Wigmore

I agree with the CMA's recommendation to lower the legal blood-alcohol concentration (BAC) for driving from 0.08% to 0.05% and with Henry Haddad's response.1 It should be noted what currently occurs in forensic practice regarding the 0.08% limit. 

Police do not routinely charge a drinking driver for an offense of over 0.08% unless one of the results of the evidential breath-alcohol instrument is 0.1%.2 In field use, the evidential breath-alcohol instruments used by the police have been found to read approximately 12% lower than the actual BAC.3 In addition, the Criminal Code allows for a 2-hour presumption, whereby it is presumed that no alcohol has been eliminated from the body during that period of time, even though the average rate of alcohol elimination found in drinking drivers is approximately 0.02% per hour.4 

Taking these factors together, it is possible that a drinking driver who had a BAC of 0.152% at the time of an accident may not be charged with over 0.08% when an evidential breath alcohol test is conducted 2 hours later. For this and other reasons indicated by Haddad,1 the CMA's recommendation of a lower BAC limit is well justified.

**James G. Wigmore** Forensic Toxicologist Centre of Forensic Sciences Toronto, Ont.

## References

1.  1. Haddad H. Blood-alcohol levels: show me the evidence [letter]. CMAJ 2002; 166(9):1132-4.
    
    

2.  2. Hodgson, BT. Alcohol. In: Chayko GM, Gulliver ED, Macdougall DV, editors. *Forensic Evidence in Canada*. Aurora (ON): Canada Law Book; 1991. p. 55-76.
    
    

3.  3. Harding PM, Laessig RH, Field PH. Field performance of the Intoxilyzer 5000: a comparison of blood- and breath-alcohol results in Wisconsin drivers. J Forensic Sci 1990;35(5):1022-8.
    
    [PubMed](http://www.cmaj.ca/lookup/external-ref?access_num=2230681&link_type=MED&atom=%2Fcmaj%2F167%2F7%2F740.1.atom) 

4.  4. Jones AW. Disappearance rate of ethanol from the blood of human subjects. J Forensic Sci 1993; 38(1): 104-18.
    
    [PubMed](http://www.cmaj.ca/lookup/external-ref?access_num=8426147&link_type=MED&atom=%2Fcmaj%2F167%2F7%2F740.1.atom) 
    
    [Web of Science](http://www.cmaj.ca/lookup/external-ref?access_num=A1993KH54100018&link_type=ISI)