Page 32 - Occupational Health & Safety, November 2018

RESPIRATORY PROTECTION
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 neu- tralize 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 oc- cupational health and safety professional can and will encounter throughout their working career. Airborne materials are often clas- sified into these major categories:
■ Gases and vapors: These substances exist in a formless state that commingles with air to create a harmful breathing environ- ment. Examples of toxic gases are hydrogen sulfide, carbon mon- oxide, 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 met- als. Examples of fume-generating processes include welding, braz- ing, 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 generat- ed 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 haz- ards accurately and repeatedly. Fortunately, a wide range of solu- tions 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 sys- tem 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 neu- rotoxins; these include many solvents and fumes that cause nerve cell death, with consequences ranging from impaired brain func- tion (lead poisoning) to ototoxin-induced hearing loss from ex- posure 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 se- rious IDLH conditions, such as toxic or explosive levels of carbon
monoxide, hydrogen sulfide, and even chlorine, has made expo- sure 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 encoun- ter, such as CO, H2S, and perhaps also measure total concentra- tion 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 ad- here) 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 chromato- graph, high-pressure liquid chromatography, or atomic adsorption analyzer to determine each compound and its precise concentra- tion level. This can be compared to the allowable TWA (time- weighted average) of exposure for each compound, and then ap- propriate 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 us- ing 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 log- ging function for download, which is extremely useful for under- standing 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
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