Wherever possible, always opt for respirator systems that offer a HEPA filtration system. These systems remove about 97% of bacteria, pathogens, and toxic fumes from the air being inhaled. To know if your Powered Air Purifying Respirator (PAPR) filter is working properly, simply use the unit in your normal work environment. If at any time you taste or smell any unusual contaminant or irritant, it means the filter needs replacing.