Fall 2008, Volume 2, Issue 1

By Gary O. Nelson and Steven J. Priante

ASTM F-739 (and the European equivalent EN 374) measures the breakthrough time for continuous contaminant contact.  The permeation test involves clamping a test article between 2 compartments of  a glass chamber (see Fig. 1).  The test contaminant (gas or liquid) is placed into one compartment (in contact with the test article) while a sweep gas (or liquid) flows through the other compartment to an analyzer. The permeation of contaminant through the material is then measured based on the appearance of contaminant in the sweep gas compartment as a function of time. If a test article is found to be protective against a certain contaminant, further tests may be necessary to make sure seams, zippers, and visor materials are providing an adequate seal.  ASTM F-1383 is similar to F-739, but this test measures the permeation rate of contaminants with intermittent, rather than continuous, contact. One other test commonly employed is ASTM F-903.  This test measures the visual or bulk transfer of liquids (penetration)

Fig. 1 ASTM Permeation Test Cell

Permeation breakthrough times of mixtures are quite difficult to predict compared to the permeation of separate pure contaminants, so that taking actual measurement is even more important for mixtures.  For example, a glove may be protective against Solvent A (very toxic), but not against Solvent B (not so toxic).  However, when Solvents A and B are mixed, the same glove may no longer be protective against A, because swelling of the glove by the more innocuous Solvent B increases the permeation of the more toxic Solvent A. 

The bottom line is this:  If there  is any doubt about the safety of protective clothing, it is prudent to conduct these relatively simple and inexpensive permeation or penetration tests.  For more information, please contact Steve Priante, Milller Nelson Analytical, 352-728-3400, Leesburg, FL.

Chemical Exposure Assessment as a First Step in Respirator Selection                             By Gus Manning

Employer Should Assess Chemical Hazards

The OSHA requirements suggest that the employer should determine the identity and concentration of chemical hazards present in

Developing a Change Schedule Using Data

If the employer knows the chemical concentrations to which workers will be exposed, one would select a NIOSH-certified respirator that fits the physical work requirements.  Then, the highest expected exposure levels (along with parameters of the selected respirator) would be entered into the "Advisor Genius" at the OSHA website, or another computerized model, to calculate the expected service life for the selected respirator.

What if the Employer Has No Data?

While OSHA allows respirator change schedules to be based on "reasonable estimates," "guesses" are not allowed.  "Where the employer cannot reasonably estimate the employee exposure, the employer shall consider the atmosphere to be (at the) IDLH."

Since IDLH conditions generally require air-supplied respirators, employers desiring to use air-purifying respirators will need to perform an exposure assessment to determine worker exposure levels.  Exposure Assessment has become a complex field, but its goal is to determine chemical concentrations in workers' breathing zones by estimation or measurement.

Where to Get Data? Estimating vs. Measuring

Some industrial hygienists say that estimating exposure levels using models and professional judgment is more cost-effective and convenient than measuring exposure levels. The two approaches can be compared by considering the following situation.

Example with Acetone and Toluene Exposures

Acetone and toluene are used in a workplace, but the levels of employee exposure are not known.  Desiring a more accurate determination (one that would be below IDLH values and could justify air-purifying respirators) the employer considers exposure assessment by an industrial hygienist using a model versus direct measurement.

Exposure Assessment Using a Model

The employer hires a consultant who performs an exposure assessment by estimation using a popular model.  Records are located which indicate that 11 L of acetone and 5 L of toluene are lost daily by evaporation into a workplace having a volume of 500 M³, that experiences one air change every hour.  The consultant charges the employer $1,200 for one day's consulting and predicts the average levels of 909 ppm of acetone and 228 ppm of toluene.

This estimate is more accurate than the worst case IDLH assumption, and produces a lower exposure estimate facilitating a more liberal respirator change schedule.  Still, it is based on estimates of solvent evaporation, room volumes, and air-turnover, and it assumes that exposure levels throughout the room are uniform.

Applying a typical workplace variation factor, the consultant might need to add 50% to the average values and estimate the "highest likely personal exposure levels" of 1,364 ppm of acetone and 342 ppm of toluene.

In reality, it is likely that workers will be located as close as possible to the incoming ventilation stream, so that the exposure level in breathing zones would be lower than the average for the room. But, the use of models usually obligates one to assume a worst case scenario.

Exposure Assessment by Actual Measurement

Two things can be said about actually measuring chemical concentrations in workers' breathing zones: (1) Personal monitoring using personal monitoring badges is more cost effective and convenient than in the past, and (2) Because all exposure assessment models must assume a "worst case," measurements almost always yield a lower exposure level than estimates from models. 

Thus, if an employer is unhappy with a respirator change schedule derived from models and worst case assumptions, it is likely that actual measurement may yield a lower exposure assessment, facilitating a more liberal change schedule.  An employer with minimal industrial hygiene training can measure full-shift acetone and toluene levels in the personal breathing zones of 10 workers for well under $1,000.

There is a good chance that using actual personal monitoring data to project the service life of an air-purifying respirator may cost less to generate and also yield a longer service life with a more favorable change schedule, than using a estimation model.  Finally, the employer has now taken the "high road" of measuring, rather than estimating.

The ISRP is a non-profit organization whose charter is "to provide an educational and informational service to all individuals involved in respiratory protection."  The Society's members span from academics to engineers, firefighters to physicians, and hygienists to defense personnel.  Since its inception in 1983, the ISRP has been disseminating research and know-how on all aspects of breathing protection.

The Davenport Hotel, Dublin, Ireland, home to the 2008 ISRP Conference

Another important activity of the Society is the publishing of its Journal, now in its 25th year of print, and a much-respected source of information among respiratory protection professionals. Each issue contains news, discussions, and many scientific and technical  papers.  The Society's active website has recently established a complete online

library of every issue of the JISRP ever published--an estimated 4,500 pages specifically related to respiratory protection.  In addition, the Society's American, European, Asian, and Australian sections occasionally arrange local workshops on current topics.

In an unprecedented initiative, the ISRP recently embarked on a world-wide educational program about occupational respiratory protection in developing countries.  In conjunction with WHO and other organizations, the ISRP will soon conduct a pilot train-the-trainer program in Cambodia--the first step towards providing an invaluable resource for safety officers, instructors and other in-situ personnel in all types of industry.

The ISRP welcomes new members from all facets of breathing protection.  Interested parties are invited to visit the Society's main website, www.isrp.com.au, or one of the Section's own websites.

If the recent conference was a 'green' one in laid-back Dublin, the next promises to step up the pace by several notches.  The ISRP conference in 2010 is set to take place in one of the world's most vibrant and dynamic cities, Hong Kong.