When should the filter on a respirator be replaced?

The correct answer is based on the operational principle of respirators and filter effectiveness. Filters on respirators are designed to capture airborne contaminants, but their efficiency diminishes over time and with use. When breathing through a filter becomes noticeably more difficult, it signals that the filter is becoming clogged or saturated with particles, which means it can no longer provide adequate protection. Additionally, if the filter appears dirty, it suggests that it's been used extensively and may not be functioning optimally.

Replacing the filter when it becomes difficult to breathe or shows visible dirt ensures that the user maintains a high level of protection from harmful substances. Factors like the frequency of use, environmental conditions, and the specific type of contaminants encountered will also influence how often filters need to be replaced, making the condition of the filter a key indicator for replacement rather than adhering to a strict schedule.