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Bitrex Respirator Fit Testing

Quick Tips #142
Testing Agents

When fit-testing respirators, a variety of testing agents are acceptable to the Occupational Safety and Health Administration (OSHA) fit-testing policies. The most common types are isoamyl acetate, commonly referred to as banana oil because of its fruit-like aroma, saccharin, a sweet-tasting agent and stannic chloride, otherwise known as irritant smoke. A new fit testing agent that has been introduced is Denatonium Benzoate, also known as Bitrex®. Bitrex leaves a very bitter taste in the mouth if masks do not fit properly.

All of these agents can be used for qualitative fit testing for negative-pressure respirators. The qualitative method is acceptable to OSHA standards (29 CFR 1910.134) and can be performed with minimal training and expense. See Quick Tips #324 Qualitative Fit Testing for more information.

Problems with Irritant Smoke

Irritant smoke, or stannic chloride, chemical formula: SnCI4; CAS #7646-78-8, gives off hydrogen chloride and tin fumes, which can be toxic. When used during fit testing, the stannic chloride reacts with humidity producing a white smoke with a pungent odor. This smoke contains two compounds: hydrogen chloride (HCL) and tin (Sn). Hydrogen chloride is highly corrosive to human tissue. Inhalation of a relatively low concentration will cause irritation to the upper respiratory tract and eyes. This is why it’s such an effective chemical to use for respiratory fit testing. When exposed to higher concentrations for a short duration, inhalation of the hydrogen chloride may cause coughing fits, chest pains, sneezing and choking. Both OSHA and the National Institute of Occupational Safety and Health (NIOSH) have established Time Weighted Averages (TWA) of 5 parts per million (ppm) for hydrogen chloride. NIOSH has also published an Immediately Dangerous to Life and Health (IDLH) level of 50 ppm for hydrogen chloride.

The second product produced by the reaction of stannic chloride and humidity is tin. Normally tin is considered a relatively safe substance. In fact, one of the most important uses of tin is in the food and beverage canning industries. However, when tin reacts with strong acids, such as hydrogen chloride, it becomes acidic. This compound causes irritation to the upper respiratory tract. Prolonged exposure to tin fumes is known to produce benign pneumoconiosis.

Problems with Saccharin and Banana Oil

Though not harmful, saccharin has a sweet taste that may not cause a strong reaction in some fit test subjects. Since the taste is a pleasant one, some subjects may not notice or acknowledge it. Others may not taste it at all.

A similar problem occurs when banana oil is used; it has a pleasant, fruit-like aroma. The drawback of banana oil is that it can only be used with organic vapor cartridges, whereas the other testing agents are for use with filters.

Bitrex Offers a New Solution

Bitrex, chemical formula: C28H34N2O3; CAS #3734-33-6, was designed for human exposure. It was originally trademarked to denature alcohol and has an intense bitter taste. It’s been added to some household chemicals and automotive products to prevent accidental poisoning. OSHA and NIOSH do not yet have TWA information for Bitrex.

In 1996, Bitrex was accepted by OSHA for respirator fit-testing for an interim period due to the concerns with irritant smoke and saccharin agents. This acceptance was based upon a study performed by H. E. Mullins, S. C. Danisch and A. R. Johnston entitled Development of New Qualitative Test for Fit Testing Respirators published by the AIHA Journal (November 1995, Vol. 56).

The procedures for the qualitative testing are easy. There are two tests to perform: a sensitivity test and a fit test.

The sensitivity test is done first to verify that the person being fit tested can detect the taste of the Bitrex solution at a diluted concentration. Following is a brief description of those procedures:

  1. Have the person put on the test hood without a respirator.
  2. Position the hood forward so that there is a six-inch gap between the person's face and the window.
  3. Instruct the person to breathe through his/her mouth.
  4. Using a nebulizer containing the sensitivity solution, inject the aerosol into the hood. Inject ten squeezes of the bulb, fully collapsing and allowing the bulb to expand fully on each squeeze.
  5. Ask the person if he/she can taste the sensitivity solution.
  6. If the person does not taste the sensitivity solution, inject an additional ten squeezes of the aerosol into the hood. Repeat again if needed. Do not exceed a total of thirty squeezes during the test. If thirty squeezes are inadequate, end the test and use a different type of fit test method.
  7. Remove the hood and give the subject a few minutes to clear the taste from his/her mouth.

Once the individual passes the sensitivity test, the fit test can be conducted. Follow these basic steps:

  1. Have the person put on the test hood with a respirator.
  2. Position the hood forward so that there is a six-inch gap between the person’s face and the window.
  3. Using the nebulizer filled with the test solution, inject the aerosol into the hood using the same number of squeezes required during the sensitivity test (See step 6 above.).
  4. Instruct the person to tell you if they can taste the Bitrex at any time during the test.
  5. To maintain an adequate concentration during the test, inject one-half of the number of squeezes used in step 3 every thirty seconds.
  6. After the initial aerosol is injected, instruct the person to perform the following exercises for 60 seconds each.
    • Normal breathing
    • Deep breathing
    • Turning head from side-to-side
    • Nodding the head up and down
    • Talking, recite the alphabet or read a passage out loud, e.g., rainbow passage
    • Normal breathing
  7. If the entire test is completed without the person detecting Bitrex, the test is successful.
  8. If the person does detect the taste, terminate the test. Wait fifteen minutes and perform the test over starting with the sensitivity test.

The person administering the qualitative fit test does not have to be certified by an organization or OSHA in order to conduct fit-testing. However, he/she should be qualified by the employer so he/she can administer the test, prepare the solutions, calibrate equipment and perform the test properly. The employer needs to certify at the conclusion of the test that the employee has successfully completed the fit test. The following items need to be on the certification form: employee name; respirator type (model and size); test date; and tester’s and subject’s signatures.


Bitrex is a safer and more reliable fit-testing agent than saccharin and irritant smoke. A fit test subject may easily avoid acknowledging a poor fit because saccharin has a sweet taste or he/she may not be able to taste it. Irritant smoke will cause the fit test subject to cough, making a poor fit evident, but the hydrochloric acid mist from the stannic chloride is also toxic. On the other hand, because of the bitter taste it leaves in the mouth, Bitrex causes an unavoidable response in the test subject, yet it is non-toxic. It is also an acceptable method for fit testing the new N, R, and P filters which meet 42 CFR Part 84 criteria for particulate filtration.


Allegro Qualitative Fit Test Kit. Part No. 2041. Allegro Ind. Inc., 1996.

Bitrex: Material Safety Data Sheet, Allegro Ind. Inc., 1996.

Department of Labor, Memorandum for Regional Administrators, Respiratory Fit Testing and Fit Checking Procedures, Washington, D.C., 1996.

Sittig, Marshall, Handbook of Toxic and Hazardous Chemicals and Carcinogens, New Jersey: Noyes Publications, 1991.

Budavari, Susan, The Merck Index, New Jersey: Mereck & Co., Inc., 1989.

Ash, Michael and Irene, Gardner's Chemical Synonyms and Trade Names, Vermont: Gower Publishing Ltd., 1994.

(Rev. 1/2013)

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Please Note:
The information contained in this publication is intended for general information purposes only and is based on information available as of the initial date of publication. No representation is made that the information or references are complete or remain current. This publication is not a substitute for review of the current applicable government regulations and standards specific to your location and business activity, and should not be construed as legal advice or opinion. Readers with specific questions should refer to the applicable standards or consult with an attorney.

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