Derived Air Concentration (DAC) is defined as the concentration of radioactive material in air that would result in one ALI if breathed for how many hours?

• A. 2000 hours
• B. 24 hours
• C. 8 hours
• D. 4000 hours

Answer: (A)

Derived Air Concentration uses the idea that the annual inhalation limit (ALI) is a yearly constraint. To translate ALI into an air concentration, we assume a standard working year of about 2000 hours (roughly 40 hours per week for 50 weeks). This makes the DAC the concentration in air that would deliver one ALI if breathed for that typical working year. The other options don’t fit because they represent daily or shift-length times, or double the typical work year, which aren’t used for defining DAC.