Construction Health and Safety Technician (CHST) Practice Test

To calculate the Time Weighted Average (TWA) for the given exposures, you first need to understand that TWA is calculated by taking the total exposure in terms of concentration over a total time period.

In this specific case, the formula for TWA can be represented as:

\[ \text{TWA} = \frac{(C_1 \times t_1) + (C_2 \times t_2) + (C_3 \times t_3) + (C_4 \times t_4)}{T} \]

where:

- \( C \) represents the concentration (in PPM)

- \( t \) represents the time (in hours)

- \( T \) is the total time of exposure

Following this for the given exposure durations and concentrations:

1. For 3 hours at 1.0 PPM: \( 1.0 \times 3 = 3.0 \)

2. For 2 hours at 1.5 PPM: \( 1.5 \times 2 = 3.0 \)

3. For 2 hours at 0.5 PPM: \( 0.5 \times 2 = 1