Monitoring for Respiratory Hazards—Challenges and Opportunities in the Workplace
Monitoring and sampling for dusts, gases, vapors, and mists should be a part of any personal exposure assessment initiative and is not only accepted practice, it represents best practice when done correctly.
- By Steve Ochs
- Nov 01, 2018
Of the "Top 10" OSHA standards that were cited in 2017, respiratory protection, general industry (29 CFR 1910.134) ranked fourth—after fall protection, hazard communication, and scaffolding. In general industry standards, only hazard communication citation was more prevalent.
Now, with the new construction standard for silica (29 CFR 1926.1153) requiring employers to limit exposure to this very common material, you can be sure more citations are going to be happening. In fact, it was reported in summer 2018 that a contractor was recently cited for willful and serious violations of the new rule for which their state' OSHA compliance office has proposed a fine of more than $300,000.
Why So Much Emphasis on Respiratory Exposures?
Occupational exposure to deadly chemical and physical agents typically occurs through one of the three common routes: inhalation, ingestion, and absorption. Of these pathways into the human body, inhalation is the fastest because the respiratory system is directly linked to the circulatory system. Thus, while the process of breathing provides us with the oxygen we need to survive, many of the contaminants that are in the air we may breathe at a work site are in a form that allows them to be deposited deep into the lungs. Because exposure to these contaminants is not always able to be removed through engineering controls and administrative controls become restrictive to production, PPE in the form of multiple kinds and types of respirators is a commonplace solution.
Among the most cited standards, respiratory protection can easily be described as perhaps the most complicated and one that presents uniquely diverse challenges to the occupational safety and health professional. When it comes to understanding the risks, quantifying exposure levels and implementing the controls needed to ensure a safe workplace for all employees under their areas of responsibility, there are literally thousands of physical and chemical agents that can cause occupational illnesses.
The Importance (and Challenges) of Monitoring Exposures
The extremely wide range of chemical, physical and even biological agents that can cause serious harm to workers spans across all industries and occupations, from those working in manufacturing and service industries to workers in agriculture, oil and gas production, chemical and pharmaceutical manufacturing, to first responders.
As such, the more you know about how to detect and monitor for the presence of these bad actors, the better prepared you and your workers will be to prevent illness, injury, or death. For the proper selection of PPE, it becomes extremely important to monitor for and/or sample the exposure levels of these airborne contaminants wherever possible, using various NIOSH-approved methods.
For an injurious or deadly material to be inhaled, it must be an airborne contaminant of certain characteristics—and a human must be in the process of breathing in the contaminated atmosphere without appropriate PPE to filter out or otherwise neutralize the hazardous agent.
What to Monitor: Types of Airborne Materials Encountered in the Workplace
Let's take a look at the types of airborne hazards the typical occupational health and safety professional can and will encounter throughout their working career. Airborne materials are often classified into these major categories:
- Gases and vapors: These substances exist in a formless state that commingles with air to create a harmful breathing environment. Examples of toxic gases are hydrogen sulfide, carbon monoxide, and chlorine. Vapors diffuse into a substance in a gaseous state but may be a solid or liquid at room temperature. Examples of vapors are methylene chloride, toluene, and mineral spirits.
- Mists: Typically, these are suspended droplets of liquid caused by condensation from gas to the liquid or by disturbing a liquid into a dispersed condition through atomizing. Examples of mists are paint mists and oil mists.
- Fumes: These are solid particles generated by condensation of vaporized material, usually after volatilization from molten metals. Examples of fume-generating processes include welding, brazing, and smelting. Examples of materials existing in fume form are lead, zinc, manganese, and hexavalent chromium.
- Dust: Particulate matter of various sizes that can be generated from processes such as grinding, blasting, or mixing. Examples of common harmful dust materials are coal, silica, and wood.
- Fibers: Fibers are solid particles with an aspect ratio (length to width, or diameter) of 3:1. Examples of harmful fibers include but are not limited to asbestos and fiberglass.
With such a diversity of physical characteristics, the categories shown here present multiple challenges for exposure assessment. There is no single sampling technique or direct reading instrument that can be used to measure levels of these airborne respirable hazards accurately and repeatedly. Fortunately, a wide range of solutions exists and must be carefully considered when you are asked to present findings of exposure for any one or more of these hazards.
Chemical hazards in the form of gases and mists are quickly taken into the body through the respiratory system. Once there, these compounds can be transferred directly to the circulatory system and distributed throughout the body to disrupt vital cellular biochemical processes, becoming an IDLH threat—immediately dangerous to life or health—often resulting in death as a result of carbon monoxide or H2S "poisoning."
Other chemical agents may attack other tissues of the body with less immediate but still devastating results. For example, there are many common substances that can be inhaled that are known neurotoxins; these include many solvents and fumes that cause nerve cell death, with consequences ranging from impaired brain function (lead poisoning) to ototoxin-induced hearing loss from exposure to organic solvents, such as toluene, which kill the sensory nerve cells of the inner ear.
Monitoring for Gases and Vapors
The development of direct-reading gas monitors for measuring serious IDLH conditions, such as toxic or explosive levels of carbon monoxide, hydrogen sulfide, and even chlorine, has made exposure assessment relatively straightforward; for instance, you can rent or purchase a personal or area gas monitor that when properly calibrated can accurately measure and track concentration levels of gas exposure throughout the work shift.
Unfortunately, most real-time gas monitors can only measure five or six of the most common inorganic gases you may encounter, such as CO, H2S, and perhaps also measure total concentration of VOCs (Volatile Organic Compounds). There are around a dozen or more gases that real-time monitors do very well with, but that leaves literally hundreds of other compounds that must be sampled and analyzed by other means. That said, real-time gas monitors are an invaluable, if somewhat limited, tool in use by virtually every occupational health and safety professional for their ability to detect, datalog, and document exposures to many gases and vapor compounds.
Sampling for Gases, Vapors, and Mists
Suppose you were working with a range of chemical materials such as isocyanates, methylene chloride, or other organic compounds whose levels could not be easily quantified by a gas monitor. What then? The use of a personal air sampling pump is required.
By attaching a "sorbent tube" (a precisely sized glass column that is filled with activated charcoal to which the various long-chain polymers and other difficult-to-measure chemicals will adhere) to the pump inlet, you can draw workplace air with all its contaminating agents through the sorbent media at a set flow rate and for a prescribed time (which are documented in the NIOSH Manual) in order to physically capture a representative sample of the air the workers may be exposed to.
After the sample is taken, it is analyzed using a gas chromatograph, high-pressure liquid chromatography, or atomic adsorption analyzer to determine each compound and its precise concentration level. This can be compared to the allowable TWA (time-weighted average) of exposure for each compound, and then appropriate action can be taken to reduce exposure through controls or facilitate the selection of the correct type of respirator to protect the worker.
There are some compounds that cannot be best sampled by using a sorbent tube, and in its place a device called an "impinger" is used to collect the sample. This uses liquid media through which the sample gas is passed, and the type of adsorbent liquid is specific to the gas or family of gases that needs to be measured.
Monitoring for Dusts and Fumes
As with gases, dust concentrations can be measured in two very different ways. One gives you a real-time indication of the levels that are present and can record results in a second-by-second logging function for download, which is extremely useful for understanding the patterns of personal exposure to dust throughout the day. The second option is by capturing a physical sample using a personal sampling pump for later analysis through varying means and methods.
Capturing What Counts—Size Matters
Not all airborne materials are considered a respirable agent. When it comes to dusts, the size of the individual particle determines whether they are dangerous enough to be respirated deeply into the lungs, thus creating either an immediate threat to the worker's cardiovascular condition by passing from the lungs directly into the bloodstream, as in the case of ultrafine metal particles (as demonstrated by NIOSH) or a long-term high probability of developing a devastating and debilitating illness, such as mesothelioma (asbestos-related cancer) or silicosis.
The three categories of dust are respirable, thoracic, and inhalable. Each type of dust exists in the air we breathe; the only difference between them is the diameter of the dust particle. Respirable dust particles are under 10 microns, thoracic dust particles are under 25 microns, and inhalable dust particles are under 100 microns in diameter.
The sampling method varies, depending upon the type of dust to be evaluated. One such method is the use of a "Cyclone"—a precisely designed and crafted chamber that uses the effect of centrifugal force to allow larger nonrespirable particles to be cast out, leaving only respirable particles behind.
Those respirable particles, 10 microns or smaller, are then captured on a filter that is housed in a "cassette" or cylindrical holder so that the material collected can be weighed and analyzed for its chemical makeup. A variety of methods are used for determining the chemical and material properties of the dust sample, including examination under an electron microscope for "speciating" or classifying different types of asbestos fibers, which have different carcinogenic properties.
Real-time Dust Measurement Versus Sampling
A real-time dust monitor typically uses an optical "forward light scattering" technique to determine the relative concentration of total dust passing through its sensor beam. The real advantage of a real-time monitor over a sampling pump for estimating personal exposures is that it gives a highly resolved picture of how the dust concentrations intensify or decrease with activities performed by the worker. For example, opening a barrel of granulated raw material and mixing it with another could produce very high levels of dust exposure for a short period of time. A sample pump, on the other hand, would be running continuously throughout the shift to be able to measure the TWA value of exposure. If that TWA were above the allowable PEL for the material in use, it could be because the levels were so high during the mixing operation that the resulting TWA indicates a respirator should be worn throughout the work shift. In this example, however, a case could be made by using a real-time dust monitor in addition to the sample pump that the respirator need be worn only during the mixing operation. This may well ensure better worker compliance when knowing they are required to wear PPE only during truly hazardous work tasks, if other controls cannot be put in place to reduce the exposure.
Monitoring and sampling for dusts, gases, vapors, and mists should be a part of any personal exposure assessment initiative and is not only accepted practice, it represents best practice when done correctly. Air sampling using a personal sampling pump can give highly accurate results but does not give time-resolved analysis of when and how the exposures occur, and this is true for all the airborne material classifications we have described here.
It is sometimes difficult to know in advance the more optimal monitoring method—and often the combination of the two approaches gives a better overall result. If in doubt, always consult an industrial hygienist, and don’t forget to use the equipment manufacturer as a knowledge base and active resource for choosing the right sampling and monitoring methods.
One thing is certain: Disregarding OSHA compliance requirements for limiting exposures for all regulated respirable hazards would be foolish and very hazardous to the well-being and health of your business, as well as that of your workers.
This article originally appeared in the November 2018 issue of Occupational Health & Safety.