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

The correct answer is P-series filters, which are specifically designed to be effective in environments where oil aerosols may be present. The designation of P in these filters stands for "oil proof," which indicates that they can filter out solid and liquid particulates, including those that are oily in nature.

P-series filters are constructed to capture a range of airborne particulates, ensuring safety in workplaces where exposure to oil mist or fumes is a concern. In situations where there might be exposure to both solid particles and oil-based aerosols, the P-series is the most reliable choice.

The other filter options do not provide the same level of protection against oil-based particulates. For instance, N-series filters are not resistant to oil, making them unsuitable for environments where oil may be present. R-series filters can be used for some oily conditions but have restrictions and limitations compared to P-series. C-series filters are typically used for gases and vapors rather than airborne particulates and do not filter solid particles effectively. Thus, P-series filters stand out as the most appropriate choice in scenarios involving oil.