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Unit 4

Unit Lesson

An important part of the industrial hygienist’s job is to recognize hazards in the workplace. Occupational

hazards can be divided into three basic categories: chemical, biological, and physical. We will be studying

chemical and biological hazards during this unit. Recognizing chemical hazards requires the industrial

hygienist to have at least a basic understanding of chemistry and biology, including the sub-science

of microbiology.

Chemical hazards are typically divided into two categories based on their chemical state. The two categories

are vapors/gases and aerosols. In the occupational setting, it is more common that the terms particle or

particulate are used. It is fairly easy to understand the differences between gases/vapors and aerosols. What

may be more difficult is to understand the difference between a gas and a vapor.

The difference between a gas and a vapor depends on the state of the chemical at normal (sometimes called

standard) temperature and pressure (NTP or STP). A gas is in the gaseous state at NTP, while a vapor is in

the liquid state at NTP with some vapors being produced. The concentration of the vapors being produced

depends on the vapor pressure of the chemical. Gases have vapor pressures that are high enough that they

do not exist as a liquid at NTP. The higher the vapor pressure is for a chemical, the more likely a vapor will be

produced. One important thing to remember is that vapor pressure is temperature dependent. As the

temperature increases, the vapor pressure of a chemical will also increase, increasing the volatility of the

compound. This can be very important for an industrial hygienist in recognizing chemical hazards. Thus, if the


Recognition of Chemical and Biological Hazards

Commonly Present in Industrial Settings

MOS 6301, Advanced Industrial Hygiene 2



industrial hygienist knows that a certain chemical with a fairly low vapor pressure is being used in a process in

which it will be heated up, there may be a significant increase in exposure levels that must be dealt with.

Another important chemical property that the industrial hygienist must consider is the vapor density.

Chemicals with vapor densities greater than one (heavier than air) will settle to lower areas when there are no

outside forces like wind or ventilation working on them. Chemicals with vapor densities lower than one tend to

rise up. If a spill or gas release occurs at a facility, the industrial hygienist should consider the vapor density to

account for concentrations of the chemical that may collect in low lying areas near the spill. Not taking this

into account has resulted in exposure to individuals entering low lying areas, such as pits, after a spill cleanup

and suffering harm or death due to the accumulation of vapors and gases.

Aerosols have chemical properties that make their recognition somewhat different than gases and vapors.

There are several general categories of aerosols, dusts, mists, fogs, fibers, smokes, and fumes. The

differences are based on the types of aerosols that are present in the air. Dusts and fumes are solid aerosols

in the air. Mists and fogs are liquid particles in the air. Smokes are mixtures of solid and liquid aerosols in the

air. Fibers are solid aerosols in the air with a specific length-to-width ratio.

Fumes are aerosols that are sometimes misunderstood by both health and safety personnel and the lay

person. The term fume has come to be used synonymously with the terms vapor and gas. It is important for

the industrial hygienist to understand the difference among these terms. A fume is generated when a solid

material is vaporized. The vapor is not stable in the air at the temperatures that are present, so very small

particles are produced. The most commonly encountered fumes in an occupational setting are welding fumes.

Understanding the difference between a fume, a gas, and a vapor is very important when determining control

methods, which we will explore in a later unit.

Another important difference between aerosols and vapors/gases is the concept we talked about involving

vapor pressure and vapor density. Vapor pressure and vapor density are not typically the controlling factors

regarding how aerosols react in the workplace. Particle size is very important in determining how an aerosol

will interact with the human body and how long an aerosol may remain airborne. In general, smaller particles

will be deposited in lower regions of the respiratory system than larger particles. This can have a great effect

on the toxicity of the aerosol. An example of this is nasopharyngeal cancer caused by exposure to some

hardwood dusts. The particles are typically too large to enter the lower regions of the lung and are deposited

in the nasopharyngeal region where the harm occurs. Understanding aerosol size can also be important in

determining control methods.

Passive diffusion can also be important for the deposition of particles if the particles are submicron in size. A

random motion is imparted to the particles by the impact of gas molecules in the lungs. Also, diffusion is an

important deposition mechanism in small airways and alveoli for particles below about 0.5 µm in size. The site

of deposition affects the severity of tissue damage, the degree of absorption, the clearance mechanisms

available, and thus, the ultimate removal of the particles. This is one factor in the toxicity of asbestos fibers,

as smaller fibers are the most active.

Biological diseases are not typically as prevalent as chemical exposures in most industrial settings. However,

in some occupational settings, biological exposures are extremely important. For example, in a hospital

setting, the industrial hygienist needs to be able to identify several biological hazards, including bacteria like

Mycobacterium tuberculosis and fungi like Aspergillus fumigatus. The industrial hygienist will also need to be

able to identify viruses such as the human immunodeficiency virus (HIV), algae, and protozoa. Controlling

biological exposures typically takes some specialty training beyond what the average industrial hygienist

requires. A better understanding of microbiology, bacteriology, and mycology are examples of additional

sciences that might be studied. The Occupational Safety and Health Administration (OSHA) has published the

Bloodborne Pathogen standard specifically to control exposures to biological hazards.

Finally, industrial hygienists must also have a good understanding of routes of exposure for chemical and

biological hazards. The dermal route of exposure presents a unique exposure that is sometimes overlooked.

Understanding which compounds are more likely to cause harm through dermal exposure and understanding

the conditions that may be present that could increase exposure through the dermal route can be very

important. An example would be exposure to hydrogen fluoride (HF). HF will initially cause burns to the skin

like other strong acids. However, HF can be absorbed through the skin. HF has a great affinity for calcium

and will bind with calcium in the blood and bones, sometimes causing a severe condition called

hypocalcemia. In places where dermal contact with HF may occur, the industrial hygienist will oftentimes 


place containers of calcium gluconate gel, which can be applied immediately after dermal exposure to bond

with the HF, preventing further harm to the individual.

Unit IV Journal

To post your Journal, click on the link above and respond to the Journal question within the “write submission” textbox. For detailed information on how to submit your assignment, go to the Submission Instructions page.


Think about your current or former place of employment. What are some chemical and/or biological hazards that you might have come in contact with there? If you had been or were currently an industrial hygienist or safety officer at the organization in question, how would go about ensuring that the health effects of those hazards were properly mitigated? 

Your journal entry must be at least 200 words. No references or citations are necessary.


Unit IVEssay

After reading the Unit IV Lesson and your assigned readings, choose three substances that were discussed. One

substance must be a gas/vapor hazard, one must be an aerosol hazard, and one must be a biological hazard.

Write a minimum of one page for each hazard you choose (a minimum of three pages total), which summarizes the

following information:

Explain whether the substance is a chemical or biological hazard, and explain how you determined that.

Explain the key chemical properties (vapor pressure, vapor density, molecular weight, relative size) as applicable, and

describe how these properties affect the different routes of exposure. Based on the chemical properties, how would you

identify which exposure route is the most important?

Analyze how the substance could enter the body through the dermal route, and discuss why the dermal route would or

would not be important.

Describe the region of the respiratory system where deposition would be expected (only for the aerosol hazard).

You should use your textbook and resources from the CSU Online Library to obtain information for this assignment. You

must use proper APA formatting for all references that you use. The title page and reference page do not count toward

meeting the required page count.

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