News
Real-Time End-of-Service-Life Indicators will Increase Reliability of Determining Cartridge Service Life
April 29, 2003
At that time, the Occupational Safety and Health Administration (OSHA) published changes in its regulations on respiratory protection, specified in Standards for General Industry 29 CFR 1910.134. The changes eliminated the subjective sensing-of-contaminants method in non-IDLH (non-immediately dangerous to life or health) environments. The new regulations required use of either one of two objective methods for determining cartridge service life.
- Equipping the respirator with an end-of-service-life indicator (ESLI) certified by the National Institute of Occupational Safety and Health (NIOSH)
- Alternatively, implementing a cartridge change schedule based on objective data to ensure that cartridges would be changed before the end of their service life
In 1998, the technology for ESLIs was very limited and would take considerable time to develop. In the meantime, respirator manufacturers developed software with complex formulas to help employers calculate the estimated service life of air-purifying cartridges for their various work environments.
Scheduled cartridge changes are a great improvement over the more subjective "sensing" method; however, determining change schedules is not an exact science. Contaminants, their concentration levels, temperature, humidity and workers' breathing rates need to be considered. Even the added safety factors depend in part on the accuracy of estimation methods and workplace variables. In addition, administering a cartridge change schedule can be time-consuming and cumbersome.
For these reasons, manufacturers of safety equipment have pursued development of end-of-service-life indicators for gas and vapor cartridges.
Types of ESLIs
Most major manufacturers of air-purifying respirators have already developed and marketed cartridges with ESLIs for mercury vapor. These ESLIs consist of a strip of colorimetric indicator positioned on the exterior of the APR cartridge. The colorimetric indicator is sensitive to mercury vapor and gradually changes color when exposed to it. When the changing color matches the color guide on the cartridge exterior, it is time to change the cartridges.
While they provide the respirator wearer with accurate verification of continuously changing air quality, these ESLIs are measuring gas and vapor contaminant concentrations immediately outside the cartridge, not the degree of contaminant build-up inside the cartridge. Cartridges with external ESLIs are the precursors of cartridges with internal ESLIs, which more accurately indicate the condition of the air that the respirator user is actually breathing.
After several years of research, North Safety Products has developed the industry's first respirators using cartridges with REAL-TIME ESLIs inside clear-shell cartridges. One type of see-through cartridge provides real-time protection against ammonia; another, against hydrogen chloride, hydrogen sulfide, sulfur dioxide and hydrogen fluoride. Cartridges with ESLI's for protection against other types of gas and vapor contaminants are under development.
K&M Inside
The successful development of these cartridges with real-time ESLIs is the result of a team effort with K&M Environmental, a recognized leader in the design and production of devices for monitoring air quality. K&M developed the indicators, which are chemically treated strips that change color in the presence of specific types of contaminants. Positioned inside the clear cartridge shell and visible to the user, the colorimetric strip changes color to accurately reflect the remaining service life of the carbon adsorbent material. A label on the outside of the cartridge provides the color guide for the respirator wearer to use in determining when to discard a spent cartridge.
For example, the ESLI inside the cartridge that protects against ammonia matches a bright yellow section on the outside label. As the ESLI inside gradually changes from yellow to blue, the color change indicates the degree to which the ammonia adsorbent is being used. The ESLI continuously reflects the depletion of the ammonia adsorbent. When half the yellow strip inside the cartridge has changed to blue, and the blue has begun to extend into the area marked by the bright blue border on the label outside, the user knows that it is time to change the cartridge. A picture on the outside label indicates when to discard the cartridge.
NIOSH Certification Testing
Not only are these cartridges the result of years of exhaustive research, they also have undergone extensive testing and certification by the National Institute of Occupational Safety and Health (NIOSH).
One set of tests was conducted to determine the safety margin of the ESLI. The cartridges with ESLIs inside were tested under normal NIOSH test conditions (at 25 degrees C and 50 percent relative humidity) with various prescribed concentrations of gas and vapor passing through them at 64 liters per minute per pair of cartridges. The NIOSH test concentrations, average ESLI service life, and service life of the cartridges for each contaminant are shown with the resulting safety margin on the accompanying chart.
|
Contaminant |
Challenge Concentration |
ESLI Service Life (Hours) |
Cartridge Service Life (Hours) |
Safety Margin |
|
Ammonia |
1000 ppm |
1.33 |
2.33 |
>10% |
|
Sulfur Dioxide |
500 ppm |
1.45 |
1.90 |
>10% |
|
Hydrogen Sulfide |
1000 ppm |
3.10 |
4.45 |
>10% |
|
Hydrogen Chloride |
500 ppm |
4.10 |
5.35 |
>10% |
|
Hydrogen Fluoride |
70 ppm |
33.00 |
52.00 |
>10% |
NIOSH requires a minimum safety margin of 10 percent of the cartridge service life for each cartridge. The safety margin exceeded the NIOSH requirement for each type of cartridge with the real-time end-of-service-life indicator.
Workplace Simulation Testing
Other tests were conducted to reproduce actual working conditions. These tests were run at the normal NIOSH conditions, but stopped at approximately 50 percent of the ESLI color change. All samples were then placed in airtight bags, simulating cartridge storage bags, and stored for several days.
The samples were then put on the test station and clean air was passed through the cartridges. The effluent side of each cartridge was monitored for any off-gassing. No off-gassing of the contaminant was detected in these tests.
The cartridges were then tested to completion and the safety margin was never compromised. All tests resulted in safety margins remaining at greater than the NIOSH minimum.
Shelf-Life Testing
After the cartridges with ESLIs inside were subjected to accelerated aging conditions, testing proved their continued effectiveness. All products were tested after three months of storage at 120 degrees F and 85 percent relative humidity. These harsh storage conditions did not compromise the ESLIs. All samples passed all of the NIOSH tests with results similar to those of the unaged products. Cartridge safety margins were always greater than the NIOSH minimum. Currently, the ESLI products have a two-year shelf life when kept in their original package.
In addition to testing under accelerated aging conditions, sample ESLIs in test packaging were placed in storage under normal conditions and tested after varying periods of months and years with similar results. As time continues to pass and additional samples are tested, the shelf life is expected to increase.
Eliminating Guesswork
The primary benefit of the real-time ESLIs is eliminating the guesswork involved in estimating cartridge change schedules, thereby making users increasingly confident of being adequately protected. Preventing cartridges from being discarded prematurely and reducing or eliminating the requirements for calculating and administering change schedules will also save your company money.
Companies that use respirators with the new real-time ESLIs for protection against ammonia or the acid gasses mentioned above have the opportunity to eliminate cartridge change schedules immediately. As real-time ESLI technology is developed further, cartridges with ESLIs inside will be approved for protection against additional contaminants, corresponding with the elimination of even more cartridge change schedules.
The currently available internal ESLI technology applies to air-purifying respirators. Further development of the technology for protection against selected contaminants with poor warning properties, such as TDI (toluene di-isocyanate), also can extend the benefits of real-time ESLIs to companies now using supplied-air respirators. Reduced or eliminated use of expensive and cumbersome supplied-air respirators will facilitate maneuverability and increase the physical comfort of workers. In addition to reducing the costs of cartridge change schedules, the elimination of some supplied-air respirators will save on the costs of supplied-air systems, including the acquisition and maintenance of associated equipment.
As the scope of these benefits indicates, the availability of real-time ESLIs inside air-purifying respirator cartridges is a notable industry development that will significantly increase the reliability of determining cartridge service life as well as reduce costs.
by
John B. Vincent, Q.S.S.P., Respiratory Product Manager and
Edna deMedeiros, CIH, CQE
North Safety Products
North Safety Products, 2000 Plainfield Pike, Cranston, RI 02921. Tel: 401-943-4400; Fax: 401-943-9360.
