First, let's get the obvious out of the way. You should change your filter if it ever goes past its stated expiration date. It is also recommended that you you replace cartridges within six months of opening them, even if you haven't used them.
Some of them, however, will need to be replaced sooner.
There is a common theory that says you should change your filter when you can taste the chemical or particulate, or if it becomes harder to breathe through the respirator. Warning methods such as these, however, should not be used to determine the service life of a respirator cartridge or filter.
Change schedules should be based on exposure estimates, manufacturer recommendations, mathematical models and tables, or thorough testing.
(Learn about The Basic Types of Respirators – And How to Select the Right One for Your Workplace.)
Several factors can influence the practical life of a respirator cartridge or filter, including:
- Exertion – A worker strenuously exerting themselves will increase their breathing rate and draw significantly more contaminant through the respirator cartridge.
- Physical fitness – Physical fitness and lifestyle can affect the amount of air a person requires. There is a mine rescue training exercise that involves shutting off the air to your breathing apparatus and re-breathing the air in a collapsible bag until the air is gone. Depending on the person, this can last anywhere between 8 to 14 minutes.
- Humidity – High humidity will take up space in the absorbent that could be used by organic vapors, thus shortening the life of the filter or cartridge.
- Number of contaminants – Most mathematical models and
laboratory tests rely on a single contaminant. However, multiple contaminants in the atmosphere can significantly lower the life of a filter or cartridge.
- Temperature – Higher temperatures can negatively affect the service life of cartridges.
- Cartridge variability – There can be some variability in the amount of material in a cartridge.
- Site conditions – Variability of site conditions can affect service life.
- Storage and care – How a person stores and cares for their respirators can affect service life.
Mathematical Models
There are several mathematical models that can predict the breakthrough time and useful life of a cartridge. These include:
- Wood math model table
- Yoon-Nelson mathematical model
- Gerry O. Wood mathematical model
MultiVapor™ Version 2.2.5
NIOSH offers a free MultiVapor™ Version 2.2.5 app for estimating the service life and breakthrough times for air purifying respirators.
Manufacturer Software
Some cartridge manufacturers provide free software to help you choose the right respirator and determine its estimated service life.
Test Equipment:
Test equipment is available to assess service life. Look for procedures and equipment for performing testing.
Summary
Whichever method you use to estimate service life of respirator cartridges and filters should be conservative to allow for variability which can affect service life. How often you replace them should be determined by a change schedule based on exposures, manufacturer recommendations, proven mathematical models, manufacturer or NIOSH applications, or testing.