Chronic exposure to dangerous organic vapors is a persistent concern in many workplace environments. Knowing when to change protective mask cartridges presents another challenge. Fortunately, ongoing research and testing continue to offer safety managers new options to help protect workers. While multiple methods exist for determining cartridge change schedules, one that can present real-time results is an end-of-service-life indicator (ESLI).
One of the latest options in ESLI technology involves visual indication – a new approach for detecting certain organic vapors. This ESLI from 3M is located inside an organic vapor cartridge. It features an easy-to-view bar that may grow over time as workers are exposed to certain organic vapors and concentrations. In appropriate environments, the progress of the bar can clearly show when it is time for a worker to change the cartridge.
The sensor technology behind the new 3M ESLI provides numerous advantages over previous ESLI technologies and can offer safety managers another choice in respiratory protection equipment to suit the needs of their unique workplaces.
Overview of 3M’s New Visual Indication Technology
The science of visual indication starts with a thin microporous material sandwiched between two reflective metallic layers in the indicator. The bottom layer is permeable to organic vapors. As organic vapors at certain minimum exposure levels are adsorbed into the ESLI, constructive interference of the reflected light produces growth of the visible indicator bar.
As part of an extensive performance evaluation, the new 3M ESLI has been tested against a range of organic vapors that represent solvents commonly used in laboratories and workplaces. Examples of organic vapors tested include the following classes: linear alkanes, simple aromatics, ketones, acetates, alcohols, halogenated alkanes, ethers, and organonitriles.
Results indicated that the new 3M ESLI optical sensor technology is broadly responsive to certain concentrations of these organic vapors. Moreover, it consistently functions in spite of changes in an environment, such as ambient humidity, temperature and exposure to other gases and particles.
Additional research continues to reveal information about the effects of these organics’ molecular properties on the sensor’s response. For example, testing shows that organics with lower vapor pressures tend to create a larger sensor response for a given concentration. Other relevant factors include boiling point, polarizability and refractive index. Correlating sensor response to these organic properties and parameters of the sensor material itself will support thoughtful R&D to improve the ESLI and may create new methods for selective vapor detection.
Advantages of an Optical Sensor
While refinement of the optical sensor technology behind the ESLI continues, it already offers a number of advantages over existing technologies. Commonly used tools for detecting organic vapors include detection tubes, photoionization detectors (PID), flame ionization detectors (FID), metal oxide semiconductors (MOS) and electrochemical sensors. Of these, only PID-, FID- and MOS-based technologies respond broadly to organic vapors and present the best opportunity for comparison.
First, the optical sensor in the new 3M ESLI is self-calibrating; its baseline is determined by its optical thickness. The comparable technologies require regular use of calibration gases to establish a baseline. Second, when viewed by a person, the optical sensor does not require any power source, such as a battery. Finally, the optical sensor has a thin-film form, thus reducing size and weight.(1)
Implementing Visual Indication Technology in the Workplace
A line of organic vapor respirator cartridges with an ESLI is now available from 3M. Grounded in the research briefly described here, these cartridges include passive visual indication to help users change cartridges at the right time when used in appropriate environments.
When selected and used properly, the new 3M ESLI is designed to indicate when to change the cartridge based on individual exposure and breathing patterns, so it also can help optimize cartridge change schedules for each worker. It can be used to complement a company’s current respirator cartridge change schedule, and in some cases replace it. For more information, visit www.3M.com/servicelifeindicator.
(1) As with any technology, however, there are also limitations to the new 3M ESLI technology, including that the sensor displays to the user in red-green colors only. A more complete list of limitations and warnings can be found in the product user instructions.