Understanding the nature of gases and vapors is fundamental to maintaining a safe and healthy work environment. These invisible hazards can pose significant risks, making it essential to grasp their properties and behaviors. Today, we’re diving into the critical topic of the nature of gases and vapors and how this knowledge can aid in managing workplace safety.
In this post, we’ll explore the physical and chemical properties of gases and vapors, how they behave under different conditions, and their implications for workplace safety. You’ll have a solid understanding of identifying and managing these substances effectively.
What You’ll Learn
- Properties of Gases and Vapors: Understand the physical and chemical properties of gases and vapors, including their behavior under various conditions.
- Behavior and Movement: Learn how gases and vapors move and disperse in different environments, affecting exposure and safety measures.
- Safety Implications: Discover the practical implications of these properties for managing and mitigating risks associated with gases and vapors in the workplace.
Introduction
Occupational exposure to chemical agents, including gases and vapors, typically occurs through two routes of entry: inhalation and absorption. Gases and vapors can be introduced into the workplace from a process or activity (e.g., chlorinating water in swimming pools and water treatment plants using chlorine gas or sodium hypochlorite). Other times, exposure may happen from an unintended process or as a byproduct of the process.
Vapors arise when a liquid exhibits a significant vapor pressure, allowing the molecules toward the top of the liquid to escape and transfer to the gaseous state.
Airborne chemical contaminants such as gases and vapors have unique characteristics that impact the risk they present from exposure:
- Their physical structure.
- Odor.
- Potential route of entry.
These properties are distinct from other airborne contaminants, such as particulates and dust.
The Physical Structure of Gases and Vapors
The first characteristic relates to the physical structure of gases and vapors and their ability to freely permeate the air. This has drawbacks in restricting the movement of a contaminant from one area to another but can be used to advantage when controlling contaminants through ventilation.
The capture velocity of gases and vapors is usually low, and the contaminant can be swept along with the existing air. Thus, gases are usually measured volumetrically, while vapors can be presented either volumetrically or as a mass per volume.
Odor
The second characteristic of gases and vapors that distinguishes them from other industrial hygiene hazards is their odor. Many gases and vapors have an odor threshold or distinctive odor that can assist in their identification as hazards. Unfortunately, although this odor is useful as a warning signal, it does not always relate to the concentration of the contaminant or the potential risk associated with its toxicity (Lamplugh et al. 2019).
The limitations of odor thresholds include:
- Individuals’ odor perceptions will vary (what one worker can perceive, another may not).
- The inability to confidently define a relationship between the presence or absence of an odor and the extent of risk to workers’ health.
- Interference from other substances.
- After exposure to some contaminants, olfactory fatigue (dulling or deadening of the sense of smell) can develop. This condition is particularly prominent when a worker is initially exposed to a strong odor, but after repeated or continued exposure, the odor is completely undetectable.
Very often, the odor threshold of a contaminant is higher than the occupational exposure standard. Therefore, even if the worker were to detect the odor of the contaminant, exposure may have already caused damage to the body. For instance, n-hexane has an odor threshold of 130 ppm, while the ACGIH recommends an exposure standard of 50 ppm (CDC 2019). Hydrogen sulfide (rotten egg gas) has an odor threshold of 0.0002 ppm, and the NIOSH 10-minute recommended exposure limit is 10 ppm (CDC 2019).
Route of Entry
Unlike dust and particulates, many gases and vapors can enter the body by absorption through the skin. This additional route of entry needs to be considered when evaluating the risk of exposure. Often, merely assessing exposure through the inhalation route will not be adequate. Solvent vapors, in particular, are notorious for defatting the skin and removing the lipid layer of the epidermis. Others can cause a hypersensitivity or allergic reaction to the skin.
Substances such as nitrobenzene, aniline, and some pesticides can pass easily through the skin and be absorbed directly into the body’s tissues. It has been recognized that mixing and spraying pesticides during windy conditions presents a higher risk than when the air is still.
This is due to the spray drift accumulating on the skin and being absorbed into the body. In the agricultural industry, there have been several instances of farmers suffering severe ill health after spraying pesticides from a leaking backpack holding the chemical or from handheld sprayers (Cerruto et al., 2018). As the backpack leaked, the farmers’ clothing absorbed the chemical and then directly into their skin.
Skin absorption of chemical contaminants typically occurs when a substance is splashed onto the skin or the skin is immersed in and directed into the substance. The effect may be acute (e.g., spillage of corrosive substance) or chronic (e.g., the narcotic effect of exposure to organic solvents).
Some occupational exposure standards provide a notation regarding the risk of exposure through the skin. This form of skin absorption can occur in several ways:
- Splashing directly onto the skin or mucous membranes.
- Splashing onto clothing followed by absorption through the skin.
- Absorption directly from the vapor where the atmospheric concentration is high (although this rarely occurs).
In some cases, other substances or mechanisms may also accelerate skin absorption. Solvents, for instance, may increase the uptake rate through the skin by defatting the lipid layer of the epidermis, making the dermis more susceptible. It has also been reported that some barrier creams could contribute to the overall absorption of substances.
Sweat can also contribute to an increased update of chemical contaminants. Wearing impermeable gloves (e.g., PVC, nitrile, butyl rubber) in warm conditions can cause the hands to sweat. This additional heat and water cause occlusion, where the substance is close to the skin and quickly absorbed through its surface. In cases where skin absorption of a substance presents a risk to workers’ health, it is always wise to adopt biological monitoring techniques in addition to air monitoring programs.
Summary
When considering health and safety risks to workers, it is important to understand the three unique characteristics of gases and vapors: their physical structure, odor, and potential route of entry.
Assessing the risk of exposure to chemical contaminants involves correctly identifying the hazard, including its state of matter, measuring the concentration of the contaminant, and comparing it with an appropriate standard. By appreciating the nature of gases and vapors, the right industrial hygiene sampling and analytical method can then be selected.
Helpful Resources
- Occupational Health and Safety Management: A Practical Approach, by Charles Reese
- Fundamentals of Industrial Hygiene, by Barbara Plog
- Gases and Vapors Blog Post, by Megan Tranter
- Occupational Exposure Limits Blog Post, by Megan Tranter
- Routes of Entry Blog Post, by Megan Tranter
Bibliography
CDC. (2019). NIOSH Pocket Guide to Chemical Hazards. CDC Centers for Disease Control and Prevention. Retrieved 2021, from https://www.cdc.gov/niosh/npg/npgd0322.html
CDC. (2019). NIOSH Pocket Guide to Chemical Hazards. CDC Centers for Disease Control and Protection. Retrieved 2021, from https://www.cdc.gov/niosh/npg/npgd0337.html
Cerruto, E., Maneto, G., Santoro, F., & Pascuzzi, S. (2018). Operator Dermal Exposure to Pesticides in Tomato and Strawberry Greenhouses from Hand-Held Sprayers. Sustainability, 10(7), 1-21. https://www.mdpi.com/2071-1050/10/7/2273/htm
Lamplugh, A., Harries, M., Xiang, F., Trinh, J., Hecobian, A., & Montoya, L. (2019). Occupational exposure to volatile organic compounds and health risks in Colorado nail salons. Environmental Pollution, 249(June), 518-526. https://www.sciencedirect.com/science/article/abs/pii/S0269749118346487
