If your workplace still uses or generates toxic substances, and employees at work are exposed to these toxic substances, you need to conduct monitoring to determine the level of contaminant in the air.
The frequency of monitoring depends on the level of contaminant compared against the Permissible Exposure Limit (PEL) stated in the WSH (General Provision Regulations) First Schedule.
The recommended frequencies are:
Ratio (in %)
of concentration of contaminants compared to PEL |
Frequency of monitoring |
| < 10% of PEL |
No monitoring is required.
A re-assessment should be carried out if there is any change in the process. |
| 10% to 50% of PEL |
At least once a year. |
| > 50% to 100% of PEL |
At least once every 6 months. |
| > 100% of PEL |
At least once every 3 months, until the exposure is reduced to be below the PEL by appropriate control measures. |