The Difference between Qualitative and Quantitative Fit Testing
The Use of Tight-Fitting Respirators in the Contemporary World.
Tight-fitting respirators have been used for occupational health and safety for the past 100 years. In 1920, The Gibbs breathing apparatus, originally designed for mine work was the first approved respirator for industrial work. (100 Years of Respiratory Protection History, 2019). Since then, different types of respirators are commonly used in worksites, mines, healthcare, building and construction etc to protect workers from airborne contaminants that pose a respiratory hazard.
If the tight-fitting respirator is not donned properly, it will not provide adequate protection for the individual against biological contaminants, dust, mist, fumes etc. and will put the worker at risk of contracting respiratory illnesses. A mask fit test ensures there are no leakages in the mask and confirms the fit of any respirator on the user’s face before it is used in the workplace. There are a number of accepted and validated fit test methodologies however the two most common are Qualitative Fit Test (QLFT) and Quantitative Fit Test (QNFT). These two methods meet the AS/NZS1715:2009 Selection, use and maintenance of respiratory protective equipment. Let us delve a bit deeper into what qualitative and quantitative fit tests are the key differences between them.
Fit Testing Procedures – Qualitative and Quantitative Fit Testing
Qualitative Fit Test – In this method, an airborne substance which as a distinct taste or smell is introduced into the testing environment. If the person detects the substance while donning the tight-fitting respirator, the test is deemed a fail and a new test should be completed after adjusting the respirator or choosing a different brand or size. If the user does not detect the smell or taste, then the test is a pass. There are four substances approved by OSHA for fit testing use:
Isoamyl acetate (banana smell)
Bitrex (bitter taste)
Saccharin (sweet taste)
Irritant smoke (coughing)
A qualitative fit test is usually used for half mask respirators (those that cover the mouth and nose) such as the N95s or elastomeric respirators. The biggest limitation of this method is it’s subjectivity in that it relies entirely on the user to detect the odour to determine if the fit test is a pass or fail. Some workers have difficulty with their ability to taste or smell and this can potentially lead to a false pass..
Quantitative Fit Test – A quantitative fit test is more objective than a qualitative fit test as it involves a specialist instrument such as the OHD QuantiFit 2 or the TSI PortaCount Respirator Fit Tester to measure the amount of leakage occurring at the face seal. The three quantitative fit test methods used by OSHA are:
Generated aerosol
Ambient aerosol
Controlled negative pressure (CNP)
Quantitative fit test can be used for any tight-fitting respirator. In CNP, fit testing instrument such as the QuantiFit 2 detects the leakage of air through the seal when the wearer breathes in. This RESP-FIT Approved method of fit testing can be performed indoors and outdoors and doesn’t require the introduction of artificial ambient aerosols as the challenge agent as it uses air!
In CNC (Condensation Nuclei Counter), the technology used by the TSI PortaCount, an ambient aerosol is used as a challenge agent to test a respirator while worn. While conducting an aerosol test, the instrument measures the concentration of the particles in the air and compares it to the concentration of the particles in the facepiece, with the ratio of the two results called the “fit factor”.
Traditional ambient air particle counting methods (CNC method) only work where there are particulates present. However, most commonly there aren’t enough present, so it needs to be artificially introduced using salt tablets, candles etc. The main disadvantage of this type of technology is it has a limited range of particle sizes in which it can measure, and the ambient sampling range does not equate to the human respirable range. Ambient aerosol counting also requires specific environmental conditions which restricts where the test can take place.
The CNP technology used by the OHD QuantiFit 2 is the new protocol for fit testing, allowing mask wearers and fit testers to conduct a fit test anywhere; indoors or outdoors as it doesn’t require a controlled environment. It can be performed in under 2 minutes and there are no ongoing consumable costs as air is used as the challenge agent. The QuantiFit 2 is also found to detect leaks in Respirators passed by CNC Technology.
