When oil may be present, which particulate filter must be used?

The correct choice is the P-series particulate filter. P-series filters are specifically designed to protect against particles and oil aerosols, making them suitable for environments where oil mist is a concern. They have a minimum efficiency rating of 95% for capturing particulate matter, which includes dust, mists, and smoke.

These filters are especially important in industries or situations where oil-based lubricants or coolants are in use, as N-series filters, for instance, are not rated for oil aerosols and can fail to provide the necessary protection when oil is present. R-series filters are designed for substances that may be replaced after a certain duration, and S-series filters are not standard classifications within the NIOSH filter hierarchy. Therefore, when oil may be present in the workplace, P-series filters are indeed the appropriate choice to ensure adequate respiratory protection.