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Question

What is the difference between qualitative (QLFT) and quantitative (QNFT) fit tests?

Answer
By Safeopedia Staff | Last updated: September 24, 2021

Respirators are designed to protect the user from exposure to various inhalation hazards, including vapors, fumes, toxic gases and particulate matter. However, a respirator can only perform this function if it fits tightly against the wearer's face and creates a protective seal.

A fit test is a procedure that is meant to assess that seal and ensure that a respirator is properly fitted to the user.

There are two types of fit test: qualitative fit tests (QLFT) and quantitative fit tests (QNFT). The main difference between the two is that a QLFT relies on a person’s sense of smell or taste to determine the fit, while a QNFT test measures the actual difference in particles in the test atmosphere versus that inside the wearer’s mask to determine its fitness in a particular environment.

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Qualitative Fit Testing (QLFT)

A qualitative fit test (QLFT) relies on the wearer's sense of taste and smell to detect whether the respirator provides a tight seal. To perform this test, the mask is donned and one of four substances is released:

  • Isoamyl acetate (banana smell)
  • Saccharine (sweet taste)
  • Bitrex (bitter taste)
  • Irritant smoke (involuntary cough reflex)

If the user smells, tastes, or is in any way affected by the substance, it means the seal does not provide adequate protection.

The qualitative fit test is normally used for half-mask respirators.

Quantitative Fit Testing (QNTF)

Unlike a qualitative test, a quantitative test relies on a machine that attaches to the respirator via a tube to detect leakage into the mask.

A QNFT test gives a numerical result called the fit factor. Quantitative fit testing is normally the preferred option for full-face respirators, although it can still be used for half masks.

Differences Between QLFT & QNFT

FACTOR

QLFT

QNFT

Fit determination

Pass/Fail test relying on an individual's senses

Numerically measured leakage, performed by a machine that calculates the fit factor

Reliability

Depends on the participant (inaccurate results if the user's senses are insensitive to smell or taste)

Highly reliable, not compromised by the user's senses

Exercise

Seven exercises: normal breathing, deep breathing, turning head side to side, moving the head up and down, talking, bending over, normal breathing

In addition to these seven exercises, this test requires an additional 15-second “grimace” test

Exposure limit

Permitted in environments where the anticipated hazard level is at less than 10 times the permissible exposure limit (PEL)

Required if a higher protection factor is needed

Complexity

Less complex and less expensive, only requiring the individual to be able to prepare the test solution

More complex and expensive due to the high cost of testing equipment

Test protocols

The acceptable QLFT protocols used are isoamyl acetate, saccharin solution aerosol, Bitrex solution aerosol, and irritant smoke (stannic chloride)

The three acceptable test protocols are general aerosol, ambient aerosol, and controlled negative pressure


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