Which statement best describes the relationship between ALI and DAC?

• A. DAC is the maximum permissible air concentration to avoid exceeding ALI for 2000 hours
• B. DAC is the concentration in air that would produce an intake equal to 1 ALI after 2000 hours of light work
• C. ALI is derived by dividing DAC by intake volume
• D. ALI equals DAC multiplied by hours worked

Answer: (B)

The key idea is that ALI is the limit on intake, while DAC translates that limit into an air concentration. DAC is defined so that inhaling air with that concentration for a standard working period delivers an intake equal to the ALI. In practice, this uses a standard breathing rate for light work and a common annual work time (about 2000 hours). So the DAC represents the air concentration that would produce an intake equal to one ALI after 2000 hours of light work. The other statements mix in either a regulatory “maximum” phrasing, omit the breathing-rate factor, or misuse the arithmetic, which is why they don’t describe the relationship as accurately.