Henry’s Law & Blood Breath Ratio

Henry’s Law states that the quantity of gas that dissolves in a liquid at standard temperature and pressure is directly proportional to the partial pressure of that gas in the gas phase. This makes it possible to quantify the relationship between the breath alcohol content and the blood alcohol content as the apparent blood / breath ratio. This ratio describes the relationship between the alcohol content of breath and the alcohol content of blood at a given point in time. It defines the quantity of breath that would contain the same amount of alcohol as a given quantity of blood.

Research demonstrates that 2,100 milliliters of deep lung air contain about the same amount of alcohol as one milliliter of arterial blood. Therefore, breath alcohol testers calculate the amount of ethanol per 210 liters of air.

Drinking and Driving Creates the Need for Alcohol Testing

As the automobile quickly became the transportation mode of choice in the early part of the 20th century, a problem quickly emerged. More and more people who were intoxicated were getting behind the wheel and driving. As alcohol-related accidents and fatalities became more numerous, law enforcement needed new tools to identify drunken drivers and get them off the roads and streets.

Breath Alcohol Testing is Developed

In the 1940s, breath alcohol testing devices were developed by a handful of manufacturers and began to be used by law enforcement. Though the earliest models were rudimentary, breath alcohol testing devices proved effective and provided immediate results where blood tests were impractical. In the years to follow, new breath alcohol testing methodologies were developed, including gas chromatography, infrared spectrometry and electrochemical fuel cell technology. Today, infrared spectrometry (IR) is the method of choice for evidential breath alcohol testing. Fuel cell-based testers have been used mainly for preliminary, at-the-scene law enforcement alcohol testing.

Breath Alcohol Testing Use Expands

In recent years, alcohol abuse in the workplace has emphasized the need for detection and intervention before costly and even deadly accidents can occur. Government regulators have mandated alcohol testing in nuclear power plants for several years, and the Omnibus Transportation Employee Testing Act of 1991 administered by the U.S. Department of Transportation now requires alcohol testing for approximately 7.5 million “safety sensitive” employees in the trucking, airline, rail, transit, pipeline, and maritime industries. Alcohol testing of these employees is done randomly, for reasonable suspicion, post accident, and in follow-up situations following any positive tests. Because of their reliability, instant results and ease of use, all confirming tests for DOT-affected employees must be done with a breath alcohol testing device.

Breath Alcohol Testing also being done by Non-Regulated Companies

Ever mindful of increasing liability, insurance premiums and workers’ compensation costs, an increasing number of non-regulated companies have begun implementing breath alcohol testing programs as part of their fight against substance abuse. Alcohol abuse costs companies billions of dollars each year. Consider that alcohol abuse causes:

  • 40% of industrial fatalities
  • 30-35% lower employee productivity
  • 20% of total company health care costs

When used as part of a comprehensive substance abuse program, using non-invasive breath testing instruments to perform alcohol testing on employees makes good economic sense.

Henry’s Law & Blood Breath Ratio

Henry’s Law states that the quantity of gas that dissolves in a liquid at standard temperature and pressure is directly proportional to the partial pressure of that gas in the gas phase. This makes it possible to quantify the relationship between the breath alcohol content and the blood alcohol content as the apparent blood / breath ratio. This ratio describes the relationship between the alcohol content of breath and the alcohol content of blood at a given point in time. It defines the quantity of breath that would contain the same amount of alcohol as a given quantity of blood.

Research demonstrates that 2,100 milliliters of deep lung air contain about the same amount of alcohol as one milliliter of arterial blood. Therefore, breath alcohol testers calculate the amount of ethanol per 210 liters of air.


Additional Resources: Alcohol Testing