Question

A worker spends 2 hours a day at a task in which she is exposed to 80 ppm methanol in the air. She spends another 1 hour per day exposed to 20 ppm methanol in the air. During the rest of her 8-hour workday she is not exposed to methanol. What is the TWA concentration of methanol that she is exposed to?

Answer 1

The Time-Weighted Average (TWA) concentration of methanol for the worker's workday is calculated as 22.5 ppm, which is determined by the exposure levels and duration throughout the day.

Step-by-step explanation:

The student has asked about calculating the Time-Weighted Average (TWA) concentration of methanol exposure over an 8-hour workday based on varying exposure times and concentrations. The TWA is a measure of the average exposure to a contaminant over the course of a typical workday, taking into account the duration and concentration of each exposure period.

To calculate the TWA concentration, the following formula is used:

TWA = (C1 × T1 + C2 × T2 + ... + Cn × Tn) / (total working hours)

Where C is the concentration during a specific time period T. For the given scenario, the formula becomes:

TWA = ((80 ppm × 2 hours) + (20 ppm × 1 hour)) / 8 hours

This results in:

TWA = (160 ppm-hours + 20 ppm-hours) / 8 hours

TWA = 180 ppm-hours / 8 hours = 22.5 ppm

Therefore, the TWA concentration of methanol that the worker is exposed to during her 8-hour workday is 22.5 ppm.