After drinking, alcohol is removed from the blood at a constant rate - Scottish Highers Human Biology - Question 15 - 2015

To determine how long it would take for a person with a blood alcohol concentration of 240 mg/100cm³ to be legally able to drive, we first need to understand the rate of alcohol removal as presented in the table.

Given that:

• The removal time for 200 mg/100cm³ is 12.5 hours
• The rate of removal suggests that it decreases linearly, we can extrapolate this rate for higher concentrations.

Since the maximum legal limit is 80 mg/100cm³, we need to calculate how long it would take to reduce this concentration from 240 mg/100cm³ to 80 mg/100cm³:

• The difference in concentration is 240 - 80 = 160 mg/100cm³.

Using the removal times from the table, we can assess that:

• 200 mg/100cm³ removes in 12.5 hours, and for 160 mg/100cm³ it takes about 10 hours.
• This calculates a rough removal rate. Taking the linearity of removal into account allows us to extrapolate that removing the remaining alcohol from 240 mg/100cm³ will take approximately:

1. From 240 mg/100cm³ to 200 mg/100cm³: assuming 12.5 hours to go from 200 down to 160 may take a similar fashion
   • Approx. 2.5 hours (from 240 to 200 = 2.5 hours)
2. Adding the 12.5 hours it takes to 200:
   • 2.5 hours + 12.5 hours + approx. time for further reduction down to near 80, it implies ending around 20 hours for safety measures considering body's complete clearance.

Thus, the estimated time is about 20 hours until a person with 240 mg/100cm³ could legally drive.