Monitoring for Respiratory Hazards – Challenges and Opportunities in the Workplace
In the USA, of the “Top 10” OSHA Standards that were cited in 2017, Respiratory protection, general industry 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, requiring employers to limit exposure of this very common material, you can be sure more prosecutions are going to be happening. In fact, it was reported in Summer 2018 that a contractor was recently cited for wilful and serious violations of the new rule for which their State’s OSHA Compliance office has proposed a $300,000+ fine. In the UK awareness is growing on the hazards of respirable silica and its long term health issues.
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, since 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 worksite are in a form that allows them to be deposited deep into the lungs. Since exposure to these contaminants are 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, which can cause occupational illnesses.
The Importance (and Challenges) of Monitoring Exposures
The extremely wide range of chemical, physical and even biological agents which 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 & 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
Gases and Vapors - These substances exist 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, which 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 repeatable. 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 bio-chemical processes, becoming an IDLH Threat – Immediately Dangerous to Life or Health - often resulting in death, such as 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 which can be inhaled that are known Neurotoxins, these include many solvents and fumes which 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, so 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 5 or 6 of the most common inorganic gases you may encounter, such as CO, H2S, and perhaps also measure total concentration of VOC’s (Volatile Organic Compounds). There are around a dozen or more gases which real-time monitors do very well with, but that leaves literally hundreds of other compounds which 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 OH&S professional for their ability to detect, datalog and document exposures to many gas and vapor compounds.
Sampling for Gases, Vapors and Mists –
Suppose you were working with a range of chemical materials like Iso-cyanates, 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 to reduce exposure through controls or facilitate the selection of the correct type of Respirator to protect the worker.
There are some compounds which 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 is a 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 need to be measured.
Monitoring for Dusts and Fumes
As with gases, dust concentrations can be measured in two very different ways, one that 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, or 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 dust, the size of the individual particles determines if 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 NISOH) 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. The use of a ‘Cyclone’ – a precisely designed and crafted chamber which uses the effect of centrifugal force to allow larger non-respirable particles to be cast out, leaving only respirable particles behind.
Those respirable particles, 10 microns or smaller are then captured on a filter which 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 only required to wear PPE 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 do 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.