Placeholder Image

字幕表 動画を再生する

  • Hello. Welcome to "Occupational Hygiene Principles". My name is Pete Raynor.

  • I’m an Associate Professor at the University of Minnesota School of Public Health.

  • The learning objectives for this module are that, by the end, learners should be able to classify the types of hazards that workers face,

  • define exposure and related terms, list the routes by which workers can be exposed to hazardous agents,

  • and describe the occupational hygiene framework of anticipating, recognizing, evaluating, and controlling workplace hazards.

  • As we begin to discuss the occupational hygiene framework, I should make the point that "occupational hygiene" is a term used

  • interchangeably with "industrial hygiene". "Occupational hygiene" is used more frequently in Europe and other parts of the world

  • whereas "industrial hygiene" is used more commonly in the United States.

  • I'm primarily going to use "occupational hygiene" in this module because I think it describes the profession more accurately.

  • The American Board of Industrial Hygiene defines industrial hygiene as "the science of protecting and enhancing the health and safety

  • of people at work and in their communities”. This definition makes sense from the standpoint of protecting people at work.

  • However, it also includes another critical aspect of occupational hygiene:

  • the protection of people in the community who may be affected by what others do at work.

  • Goelzer defines occupational hygiene as "the science of the anticipation, recognition, evaluation,and control

  • of hazards arising in or from the workplace and which could impair the health and well-being of workers,

  • also taking into account the possible impact on the surrounding communities and the general environment."

  • This second definition of occupational or industrial hygiene is more comprehensive.

  • I also like that it includes the occupational hygiene framework of anticipating, recognizing, evaluating, and controlling hazards.

  • We need to be able to understand when potential hazards may be present, notice them when they are there,

  • know how to determine if they are a problem, and then do something about them if they are a problem.

  • With whom do occupational or industrial hygienists interact?

  • They interact with people on the job. Most important are the workers.

  • However, this also includes the owners, managers, and supervisors of different workplaces without whose support we can get

  • little accomplished, regulators like those that work for the Occupational Safety and Health Administration or OSHA

  • at either the federal or state level, and members of the public who may be affected by what goes on at the worksite.

  • Occupational hygienists interact with their colleagues in other health and safety fields including occupational physicians,

  • occupational health nurses, safety and environmental specialists, occupational epidemiologists,

  • and occupational hygiene technicians who may carry out some of the measurements and sampling that are designated by hygienists.

  • Finally, occupational hygienists also interact with engineers and facilities and maintenance personnel.

  • Engineers may be tasked with carrying out changes in workplaces to make them more healthy or safe,

  • and facilities and maintenance personnel can affect workplace health and safety by the regular maintenance they conduct,

  • the cleaning that they do, and other changes that they may make to work environments.

  • Let’s talk next about anticipating and recognizing hazards.

  • The way I'm going to do that, at least initially, is to talk about my high school job

  • I worked at a grocery store in Irondequoit, New York, a suburb of Rochester.

  • I worked there from late in my junior year of high school through the summer after my sophomore year in college.

  • When I went to work at the grocery store, my first job there was to collect carts outside.

  • Today, many cart pushers have automated, battery-powered pushers to move trains of carts.

  • Back when I did the job, I worked much like the person in this image: we assembled long trains of carts and pushed them across the parking lot.

  • So, there was a lot of a heavy pushing, and there was also a chance to get your fingers pinched between the carts.

  • It was hard, tiring work. We would sometimes make very long trains of carts on purpose to see how long we could make the train and still

  • push it back to the front of the lot. Sometimes, the long trains got a little out of control and hard to stop because they had so much momentum.

  • We had to be concerned about vehicles in the parking lot. Often, the parking lot was congested, particularly at busy times around

  • holidays or on weekends. Although I was never injured by an incident with a car, there were many close calls and I had to watch myself

  • around cars that were moving too fast or were having difficulty backing out of a parking space.

  • During different times of the year, we were exposed to either heat or to cold. Because Rochester, New York is on Lake Ontario,

  • we had a lot of lake effect snow and frequently it would be slippery in the parking lot during the winter in addition to it being cold.

  • In the summertime, it could be very hot and we would feel it after four hours of pushing carts around.

  • We would sometimes be faced with shoplifters when we worked outside the store.

  • On one particular occasion, I was collecting carts on a sunny afternoon.

  • I was out there by myself, it wasn’t very busy, and I was off in my own little world as I was picking up carts.

  • So, I wasn’t really paying too much attention to what was going on other than in my own immediate vicinity.

  • Suddenly, I saw this guy running toward me, and as he got closer, he yelled to me, "Don't do it, man! Don't do it!" I'm thinking to myself,

  • "Don't do what?" The guy ran past, and I was still trying to understand what he meant, when my supervisor runs up to me and says,

  • "Pete, why didn’t you stop him?" I thought to myself, "Stop what?" I had no idea what was going on. It turned out that he was a shoplifter.

  • So, there was a risk that, had I realized what was going on and tried to intervene, I could've been subjected to some violence.

  • My supervisor was a little disgusted with me for not divining that I should have stopped the guy.

  • This particular supervisor didn’t like me very much, and it was sometimes stressful to deal with him.

  • Eventually, I was given the opportunity to move inside, at least most of the time, and be a checkout clerk, which involved scanning a lot of

  • items, putting them into bags, and lifting the bags up and over a shelf to put them into the customersshopping carts.

  • I would also have to enter numbers into the keypad on the register. Shifts on the registers could last as long as eight hours with

  • a lunch and two short breaks. Standing in one place and repeating these same actions over and over was tiring.

  • One of the other things I would sometimes do when I worked inside was to go to the

  • back room of the store and bring sacks of paper bags – 500 per sackup to the front end.

  • We didn’t have plastic bags back then, so these were thick paper bags.

  • I would take a large cart to the back room, go into the truck trailer where the sacks were stored,

  • climb a pile of sacks, toss about 15 sacks from the pile onto the bed of the trailer,

  • pick the sacks up and pile them onto the cart, and push the heavy cart through the store to the front.

  • Once there, I would have to unload sacks by each register, open the sacks with a box cutter, and stack the bags in the storage area

  • below the register where the clerks could pull them out and use them for customers. It was a pretty tough job.

  • When I worked inside at the front end, there was always a chance that we would have to deal with those shoplifters.

  • One time, a couple of us chased after some shoplifters who were trying to steal beer late at night.

  • We got out into the parking lot and found that we were a little outnumbered because the shoplifters were part of a larger group.

  • Fortunately, the shoplifters and their friends decided to leave the beer on the ground and drive away rather than forcing a confrontation.

  • Another time, several of us were working up front, and a car pulled up outside the front window of the store right near us.

  • A bunch of guys piled out of the vehicle after popping the hood, and we could see that there was a fire in the engine compartment.

  • We were, naturally, concerned about this, as you might expect. After a frantic few seconds discussing what we should do,

  • I ran out of the store with our fire extinguisher and put out the fire, trying to keep as far away as I could.

  • We were surprised about 10 minutes later when the guys piled back into the car and drove away.

  • I'm not sure how far they got; it was a topic of discussion for my co-workers and me for the rest of the evening.

  • Among some of the other duties I had was occasional maintenance work, especially on weekends.

  • There was one time on the Monday of Labor Day weekend that I had to clean both the men's and women's bathrooms for the store.

  • It was clear that they had not been cleaned since the previous Friday, and it was a pretty eye-opening experience

  • to have to clean those restrooms after that amount of time. In short, it was not a fun job.

  • There was lots of nasty stuff in the bathrooms, and a variety of cleaning products needed to be used.

  • Another one of my occasional tasks was to take materials to the back room to be disposed of.

  • Large groups of fluorescent bulbs are changed out at the same time in stores to make the task easier logistically.

  • This was the early 1980s: the fluorescent light bulbs were not recycled at that time.

  • When I was asked to dispose of the bulbs that had been changed out, I would take barrels full of them back to the trash compactor in the

  • back room, pile them into the trash compactor, close the door to the compactor room, press the button to turn the compactor on,

  • and we would then hear the bulbs shatter in the compactor. As a teenager, this was a pretty cool thing to hear all the crashing and smashing

  • and eventually, after the compactor had stopped, we would open the door,

  • and we could see an almost magical haze of shiny glass particles floating in the compactor room. It was awesome to look at, man!

  • Probably the most fun I had on the job was on one full-day shift on the Saturday after Thanksgiving when my co-worker Todd and I

  • had the opportunity to hang holiday decorations for the entire day. We climbed ladders and reached out to hang things across the ceiling,

  • We climbed ladders outdoors and hung garlands and decorations across the front of the store. There was a lot of climbing up and down and

  • reaching this way and that, but it was a really fun day because it was an unusual task to get paid to do. We enjoyed it quite a bit.

  • By this point, you may be wondering, “Why is this guy droning on about his high school job?”

  • Well, let’s think about my job and about the potential hazards that I faced on the job.

  • There were hazards that could have caused unintentional injuries: fires like from the car, vehicles in the parking lot,

  • slips in the parking lot when I pushed carts, falls from ladders when I hung holiday decorations, sharp objects like box cutters,

  • and pinch points like when the carts come together and you pinch your fingers as you try to line them up.

  • In addition to the unintentional injuries, there was a risk of intentional injuries. Violence was a risk particularly when I faced shoplifters.

  • Repetitive motion injuries were quite possible. I faced the risk of an injury to my back from pushing carts,

  • lifting sacks of bags in the back room, and lifting full bags into customers' carts at checkout.

  • Wrist injuries were possible from continually scanning items at the checkouts for long periods of time.

  • Temperature extremes when I worked outdoors, both when it was hot and cold, could have led to heat or cold strain.

  • I was exposed to germs at work. Because I was dealing with members of the public,

  • I could've been exposed to their germs as they sneezed or coughed near me and when I handled their money.

  • There were also the times when I cleaned the public restrooms when there was a potential for exposure to germs.

  • Chemical exposures from cleaning chemicals and the mercury in the fluorescent bulbs could have been a health concern, too.

  • Even stress could have been a concern. I knew that my supervisor didn't like me very much.

  • If I had cared more about the job than I did, I may have felt stress that could have impacted me negatively.

  • There was a whole range of different hazards that I was potentially exposed to in my workplace.

  • Although you may have been able to anticipate that grocery workers face workplace hazards, most of you, unless you've worked

  • a very similar job, would not have been able to recognize all of these different hazards.

  • This is an important point because when you are trying to anticipate and recognize hazards,

  • you really need to get to know the job before you can be effective at analyzing the hazards.

  • Ultimately, workers are the experts on their own jobs. If you are trying to understand where there

  • is a potential for hazardous exposures to whatever sort of agent you're concerned about, you need to talk to the workers.

  • If we generalize and categorize some of the hazards that exist in different workplaces,

  • we can anticipate and recognize chemical hazards that include airborne particles such as nanoparticles.

  • Workplaces may contain different gases and vapors, and especially solvent vapors as many, many solvents are used in industrial settings.

  • Heavy metals may be present, including molten metals, metals used in electronics production, and metals released to the air during machining.

  • A large variety of skin irritants may be present as well, with dermatitis being one of the most common workplace diseases.

  • There are physical hazards, hazards that affect the senses or the whole body.

  • These include noise, ionizing and non-ionizing radiation, and hot and cold temperature extremes.

  • We can anticipate and recognize biological hazards, including infectious disease agents,

  • which can be of particular concern in the healthcare industry, and mold.

  • Agriculture workers may face mold in outdoor environments or in barns,

  • and construction workers may be exposed to mold during renovations.

  • Offices that have experienced water damage may see mold growth in walls, ceilings, and carpeting.

  • There are injury hazards. Unintentional traumatic injuries can occur.

  • These include vehicle crashes, which are one of the most common causes of fatalities on the job.

  • Violence, either among co-workers or involving both workers and people from outside the workplace, is an important occupational hazard.

  • In addition, poor ergonomic conditions, including repetitive motion, awkward posture, and heavy lifting, may lead to musculoskeletal disorders.

  • Occupational hygienists may be able to anticipate, but find it hard to recognize,

  • social and behavioral hazards like stress, sleep deprivation, and substance abuse.

  • These hazards can make it difficult for a worker to perform her or his job safely

  • and in a healthy manner, in addition to being risk factors on their own.

  • and in a healthy manner, in addition to being risk factors on their own.

  • Let's move on and talk about evaluating hazards. Why would we want to evaluate hazards? I list six purposes here.

  • Let's move on and talk about evaluating hazards. Why would we want to evaluate hazards? I list six purposes here.

  • First, we might evaluate hazards for compliance purposes. The goal is to compares workers' exposures to an exposure limit or a standard.

  • For example, we can compare sound levels in a metal stamping operation to the

  • Occupational Safety and Health Administration's permissible exposure limit for noise.

  • We might try to measure levels of a hazardous agent throughout a work environment with a goal of identifying the source or sources of the agent.

  • An example would be to create a concentration map, almost like a topographical map,

  • of a machining facility to identify the sources for emissions of oil mist.

  • In emergency situations, we might seek to detect hazards that are immediately dangerous to life and health.

  • An example is the need to monitor hydrogen sulfide levels when workers enter a manure pit to perform maintenance or cleaning.

  • Control measures might need to be evaluated. The goal in this case would be to ensure that interventions designed to reduce hazardous

  • exposures are working as planned. An example of this is a series of measurements performed to ensure that airborne particles containing mouse

  • urine proteins are kept within ventilated enclosures during the change out of research animal cages in university settings.

  • We might also evaluate hazards as part of research.

  • The goal will depend on the hypothesis that is being investigated, which is sometimes part of a larger occupational epidemiology study.

  • An example of this that I worked on was when we measured silica dust concentrations as part of an epidemiological study

  • to determine the effect of the dust on the lung health of taconite ore miners on the Iron Range in northern Minnesota.

  • Finally, we might evaluate hazards for risk assessment purposes.

  • In a sense, all of these other purposes are forms of informal risk assessments. Here, however, I'm talking about a formal risk assessment

  • where the goal is to calculate exposure and/or dose for a worker exposed to an agent of concern, so that we might compare

  • that exposure or dose to the potential health effects from the dose in order to characterize the risk of an adverse health outcome.

  • An example is to measure radon concentrations in building subbasements to estimate cumulative doses that workers receive.

  • We will talk more about risk assessment and risk characterization in the next module.

  • How do we go about evaluating hazards? One way is by measuring them. We may measure a hazard to detect it, just to see if it is there or not

  • or we may want to know its concentration in a medium like food, water, or, especially in occupational settings, air.

  • In addition to measuring agents in the environment, we can measure things called biomarkers within exposed people.

  • In our context, biomarkers are substances measured in some part of the body that indicate the presence of an agent in the body.

  • A biomarker may include a chemical of concern or its metabolite, or some other biologic indicator of exposure.

  • This "biomonitoring" can be performed on samples of urine or blood or you can measure substances in tissues or hair samples.

  • We can attempt to evaluate hazards using modeling. We are not able measure everything everywhere at all times.

  • One way to get around these limitations is to use mathematical models to estimate exposures. The models can be used to predict

  • concentrations or other relevant measures of exposure as a function, ideally, of both time and location.

  • Ultimately, we will compare these measurements or modeling predictions to some sort of occupational exposure limit.

  • These occupational exposure limits are developed through the risk assessment process,

  • which, as I mentioned previously, will be discussed in a future module.

  • In short, we relate health risk information from toxicological and epidemiological studies to exposure or dose data,

  • decide what is an acceptable risk, and set an exposure limit accordingly.

  • When making measurements after performing the risk assessment,

  • we can compare our findings to the exposure limit to determine whether the workplace may be unduly harmful to people.

  • We can start to discuss controlling hazards by taking a look at some relevant definitions.

  • The vocabulary used may vary depending on one's perspective.

  • We can think about "managing" hazards. Merriam-Webster defines "manage" as "to work upon, or try to alter for a purpose".

  • The term "limit" is defined as "to curtail or reduce in quantity or extent".

  • To "intervene" is "to come in or between by way of hindrance or modification".

  • Finally, to "control" is "to reduce the incidence or severity of, especially to innocuous levels".

  • In many cases, these four words are used interchangeably when talking about ways to reduce exposures.

  • The default word is often "control", but "control" doesn't appeal to some experts because it implies that you are always able to make the

  • changes that you would like to in order to reduce exposures to hazards. The term also lends itself better to technological approaches to

  • reducing hazard levels, whereas words like "manage", "limit", and "intervene" seem to leave open a broader array of approaches.

  • In the way that I use the term "control", I intend to leave open a wide variety

  • of means for reducing exposures, not only technological options.

  • We are going to use the word "control" going forward in this module, but keep in mind that the other words convey equally valuable concepts.

  • We refer to a "hierarchy of control" when discussing approaches to reducing hazard levels.

  • The hierarchy goes from most preferred at the top to least preferred at the bottom. At the top is elimination of the hazardous agent.

  • Can you just completely get the hazard or the process that generates it out of the workplace so that it's not an issue anymore?

  • That option is rarely viable because it would involve removing a process or a product that is essential at that place of work.

  • Next on the hierarchy are engineering controls, which are physical, chemical, or biological changes made to a process or a product

  • that reduce exposures to the hazard. Third on the hierarchy are work practice and administrative controls, which are changes in

  • how, when, or by whom tasks are performed in order to reduce exposures.

  • At the bottom is personal protective equipment, or PPE, devices and garments worn by workers to protect themselves from injury or illness.

  • Let's talk a little more about why these approaches are placed in the hierarchy in the order that they are.

  • Elimination is at the top because it is completely effective for all workers,

  • and because the responsibility for change is not placed on the exposed person.

  • Engineering controls are second on the hierarchy because, even though they don't completely eliminate the hazard,

  • measures are put in place that should reduce exposures for everyone,

  • and the responsibility is not placed on individual workers to reduce their own exposures.

  • Engineering control includes a variety of concepts such as substituting one type of material for another in a process or a

  • product, using automation so workers do not need to be as close to a hazard, isolating the person from the process generating the hazard

  • or isolating the process from the person, drawing contaminated air from a process away from workers using ventilation,

  • and installing control equipment such as an air filtration unit to separate a hazardous agent from the medium in which it is embedded.

  • Work practice and administrative controls are lower on the hierarchy

  • because both management and exposed workers are responsible for making changes.

  • Therefore, we are starting to rely on people to always perform their work in a certain way or at a certain time, which may be difficult to achieve.

  • Finally, personal protective equipment is the least preferred approach when other options

  • are feasible because individual workers must use the PPE correctly each and every time they

  • perform the task that creates the hazardous exposure in order to be sure that they are not exposed to the hazard.

  • Ventilation is an important concept that we should spend a little extra time talking about. In particular, I will focus on local exhaust ventilation

  • systems, which are intended to draw contaminated air away from close to the point of generation before workers can be exposed.

  • There are many different types of local exhaust ventilation.

  • These types include exterior hoods. Both images in the upper left show a flanged opening connected to a flexible duct.

  • A fan or blower downstream draws contaminated air into the opening during the

  • cleaning of a chamber in which nanoparticles have been produced.

  • Because the opening, in essence, needs to reach out and bring in the contaminated air, it is an exterior hood.

  • Another type of exterior is shown in the other image. This is a slotted hood where air is drawn through slot openings,

  • taking away particles and vapors that are produced in front of the slots.

  • This is an exterior hood because the hazardous pollutants are outside the hood and must be drawn into it.

  • Another category of local exhaust ventilation is partial enclosures.

  • An example of a partial enclosure is the laboratory hood on the lower left, in which any process generating pollutants is enclosed

  • on at least five sides and the pollutants are drawn away with the air flowing into the hood.

  • This air enters the hood through the sixth side where workers can access the process.

  • On the right is a drawing of a bagging process. There is a clamp over the opening to the bag from which, ideally, little dust will escape.

  • To ensure that any dust that does escape does not present an inhalation exposure risk to workers,

  • there is a partial enclosure around the bag filling area that is ventilated and will draw away any dust that escapes through the clamp.

  • Partial enclosures combine the concepts of isolation and ventilation, but they are not complete enclosures.

  • A ventilated glove box can be thought as virtually a complete enclosure. Workers can put containers of potentially toxic materials

  • inside the glove box, use the gloves to open the containers, manipulate the materials with any

  • releases into the air being drawn away by the ventilation, close the containers again, and then remove the containers safely from the glove box.

  • Let's consider work practice and administrative controls next. Work practice controls alter how workers perform a task.

  • Ways in which someone can do work differently might include scooping powders rather than pouring them from containers in order to reduce

  • airborne dust exposures, regular maintenance of equipment, regular cleaning of work surfaces, using wet cleaning instead of dry methods so

  • that not as much dust is produced, washing hands properly to prevent exposures to agents on hands when workers eat or go home,

  • continuing education and training on how to work safely and in a healthy manner, and emergency drills so that workers know

  • how to exit their workplace while making sure to shut down critical processes that pose risks to responders on the way out.

  • Administrative controls are measures that change when and by whom work processes are conducted.

  • Examples include restricting access to areas with potential hazards so that fewer people will be exposed,

  • the use of hot, warm, and cold zones during the response to a hazardous materials spill where only a few people with high levels of

  • personal protective equipment are allowed into the hot zone, security procedures to ensure that

  • only people who are supposed to be at a work site are present, limiting work time to reduce mistakes due to sleep deprivation,

  • and scheduling potentially hazardous work operations during shifts when fewer workers are present.

  • On its web site, OSHA states the following about personal protective equipment:

  • "When exposure to hazards cannot be engineered completely out of normal operations or maintenance work,

  • and when safe work practices and other forms of administrative controls cannot provide sufficient additional protection, a supplementary method

  • of control is the use of protective clothing or equipment. This is collectively called personal protective equipment or PPE."

  • The kinds of PPE that people wear to protect various parts of the body range from hard hats and safety glasses to hearing protection,

  • respirators, gloves, safety shoes, and protective clothing. There are many different types of PPE within each of these classifications.

  • The different kinds of protection need to work together and they can be very effective, but they require workers to use them properly.

  • A worker wearing personal protective equipment must be attentive every single time she puts it on and takes it off.

  • Otherwise, the PPE may not protect effectively against harmful exposures.

  • It’s challenging to be consistent with the use of PPE so that the protection can also be consistent.

  • Let’s introduce some general concepts regarding exposure and dose.

  • Exposure can be defined generically as "the intensity of the agent in question, time-averaged in some way relevant

  • to the adverse health outcome, at an appropriate interface between the environment and the population or individual at risk".

  • I have underlined and highlighted three sets of words, starting with "intensity".

  • Part of exposure is the amount of some potentially-hazardous agent. I’ve also highlighted "time-averaged", as there is also

  • a time component to exposure. Because exposure takes into account both quantity and duration, a higher exposure can occur if

  • either a greater amount of an agent is present or if a worker is in the presence of the agent for a longer time. They are both important.

  • I have also highlighted "appropriate interface" because exposure must be measured at the interface of the person with the surrounding

  • environment. The best interface for an airborne exposure might be if you could put some sort of sampler directly in front of a worker’s nostrils.

  • However, that's not very practical. Instead, we often try to locate a sampler in what we call the breathing zone of a worker

  • by hanging the sampler on a worker’s collar so that it is close to where the worker breathes, without interfering with the breathing.

  • A generic definition of dose is "the cumulative amount of a property derived from an exposure

  • that drives a biological response within the exposed organism".

  • I have highlighted the words "cumulative amount" because a dose accrues over time as a worker is repeatedly exposed.

  • I’ve also highlighted the words "within the exposed organism". This is important.

  • While an exposure to an agent is outside the person at the interface of the person with the environment, dose is what gets inside.

  • This is the main difference between exposure and dose.

  • This diagram is from a paper by Sexton and co- authors. It shows the environmental health paradigm.

  • We think about agents being emitted into the atmosphere of a workplace environment. There is a source that emits the agent into the air or

  • another medium, and there are pathways by which the emitted agent moves through the workplace before it reaches a person.

  • The agent is present at some sort of concentration, referred to as an exposure concentration, in the vicinity of the worker.

  • If the exposure is through the air, we can measure the exposure concentration

  • by sampling the air at an interface of the worker with the environment.

  • The agent can be inhaled or ingested or move through the skin to form a potential dose inside the body.

  • Some of the agent that gets inside the body may not be available for uptake, or some may be immediately removed

  • such as when you exhale a portion of a pollutant that you have just inhaled.

  • So, while this portion of the agent may be part of a potential dose, it is not being applied to the body. The portion that is applied to the body

  • for example, the fraction of incoming particles that deposit in the lungsis referred to as the applied dose.

  • Some of the applied dose may not be absorbed into the body; it may be excreted instead.

  • That portion which is absorbed is referred to as the internal dose.

  • From the internal dose, we move more into the realm of toxicology where materials may be delivered to certain organs or organ systems,

  • they may or may not have a biological effect after delivery, and those effects may or may not be adverse.

  • During the rest of the module, we will focus on how to calculate exposure concentrations, potential doses, and internal doses.

  • From Sexton and coauthors, a more formal definition of "exposure" is "contact of a biologic, chemical, or physical agent

  • with the outer part of the human body, such as the skin, mouth, or nostrils". This is similar to the definition that we looked at previously.

  • "Exposure concentration" is "the concentration of an environmental agent in the carrier medium at the point of contact with the body".

  • It’s an intensity or a quantity, as weve seen before, at the interface of the environment with the body.

  • "Potential dose" is "the amount of the agent that is actually ingested, inhaled, or applied to the skin."

  • And the "internal dose" is "the amount of the agent absorbed,

  • and therefore available to undergo metabolism, transport, storage, or elimination".

  • When we talk about exposure intensity, there are various metrics that we can consider.

  • The best metrics are ones relevant to the health outcome associated with exposure to the agent being investigated.

  • We can consider metrics like mass concentration, for example the milligrams of some substance per cubic meter of air.

  • Mass concentration is a common metric for measuring exposure concentrations of gases, vapors, and airborne particles.

  • For number concentrations, the number of microorganisms per unit volume or unit mass of air, water, or food is a common example.

  • Another example is the measurement of airborne fibers, when air samples are analyzed for the number of fibers per volume of air.

  • Intensity is measured for sound pressure levels using decibels. This is the basic unit for measuring exposures to noise.

  • Different units of concentration are used for different media. In water, we use units such as parts per million, parts per billion, or parts per

  • trillion. These units refer to the mass of the potentially-hazardous agent per mass of water. Taking into account the density of water,

  • it can be shown that one part per million of a substance in water is equal to one milligram of the substance per liter of water.

  • Similarly, one part per billion is equal to a microgram per liter, and one part per trillion is equal to one nanogram per liter.

  • For air, it’s different. For gases and vapors, we use units of parts per million or parts per billion,

  • but in air these units are considered to be on a mole-per-mole basis. While these units sound the same as the ones for water, they are not.

  • An entirely different conversion is required to convert from a measurement of mass per volume of air to parts per million or parts per billion in air

  • This conversion is based on the density of air rather than the density of water.

  • For airborne particles, mass per volume is preferred with units such a milligrams per cubic meter or micrograms per cubic meter.

  • For dose, we can calculate both dose and dose rate. Dose is typically specified in mass units for chemical doses:

  • the mass of a chemical taken in by a body during a specified time interval.

  • Dose rate is usually specified in units of mass per time for chemical doses.

  • Milligrams per day would be an example for dose rate whereas dose would just be milligrams.

  • Dose and dose rate can be normalized to an individual’s body weight, for example, milligrams per kilogram

  • of body weight for a mass-normalized dose or milligrams per kilogram per day for a mass- normalized dose rate.

  • There are a variety of routes of exposure. The three most common ones that we consider are inhalation (breathing in),

  • ingestion (swallowing water or food), and dermal exposures. However, there can also be exposures through the eye,

  • referred to as ocular exposures, auditory exposures through the ear, and whole body exposures to hazards like vibration or radiation.

  • Let’s discuss exposure and dose quantitatively.

  • We can define cumulative exposure over a certain time interval mathematically using this formula.

  • Cumulative exposure, E, is equal to the concentration as a function of time multiplied by the differential of time, dt,

  • integrated over an interval of time from t1 to t2. An integral is a calculation of an area under a curve.

  • If we think about a curve of concentration as a function of time and then calculate the area under that curve between two times of interest,

  • that is the same as performing an integration and would give you a cumulative exposure.

  • Average exposure concentration, c-bar, can be determined by taking the formula for cumulative exposure,

  • concentration times dt integrated from t1 to t2, and then dividing it by dt integrated from t1 to t2.

  • That is equal to the cumulative exposure, E, divided by delta t, the duration of the exposure, t2 minus t1.

  • Rearranging terms shows that the cumulative exposure is equal to the average concentration times the duration of exposure.

  • This is a good point, while we're thinking about exposure being equal to concentration multiplied by a duration of time,

  • to think about acute versus chronic exposures. Exposure is influenced by both quantity and duration.

  • Acute exposures to hazards typically have large quantities and short durations,

  • whereas chronic exposures typically have small quantities and long durations.

  • There are many types of exposures that are acute and many types that are chronic.

  • Sometimes, the same agent could be both an acute and a chronic hazard.

  • For instance, smoke from a structure fire can be an acute exposure that can produce very damaging health effects like smoke inhalation

  • over a short period of time. However, smoke from wood stoves, backyard fires, and other sources

  • to which people are exposed may not create an immediate health effect, but with chronic exposure over a period of many years,

  • those exposed may experience adverse health outcomes including respiratory diseases and even cancer.

  • Because both acute and chronic exposures can be important, when and how long we measure exposure matters a lot.

  • This is a plot of concentration on the vertical axis versus time on the horizontal axis. If the time interval were concerned about

  • lasts from time t0 on the horizontal axis to time t0 plus capital T, we might consider that to be most of a workday.

  • The plot of concentration versus time changes a great deal as a function of time over this workday.

  • The area under the curve, the gray area, is the cumulative exposure, the integral of concentration multiplied by time.

  • The horizontal line drawn across the gray area that is labeled c-average

  • is the average exposure concentration over the time interval from t0 to t0 plus capital T.

  • The area of the rectangle created by C-average has the same area as the gray area under the original curve.

  • That's all an average is: it’s the value that creates a box that possesses the same area as the area under the original curve.

  • The gray area is an example of the type of measurement we would make to assess a chronic exposure.

  • For these exposures, we often take measurements that last an entire workday.

  • However, if we're more interested in an acute exposure, the peak exposure that might cause an acute health hazard,

  • we might need to make a very short term measurement that would pick up this peak concentration

  • and compare that short-term exposure concentration to the risk from that exposure.

  • So, the duration of exposure may be very important depending on the type of health outcome we're interested in.

  • Moving on, potential dose is equal to the integral from time t1 to t2 of concentration multiplied by

  • a term we will refer to as the instantaneous contact rate multiplied by the differential of time.

  • The contact rate for inhalation exposures is the inhalation rate or breathing rate that may be in units of liters per minute, for example.

  • For food or water, contact rate might be the mass or volume of food or water consumed per day. It is how much of the medium

  • air, water, or foodthat the exposed person takes in per unit of time. In occupational hygiene, we frequently set potential dose

  • equal to the average concentration times an average breathing rate times the duration of time exposed.

  • Potential dose rate is dose divided by the integral of time.

  • This is equal to the average concentration times the average breathing rate times the exposure duration divided by the total time elapsed.

  • The elapsed time may or may not be equal to the time exposed. We will look at an example of this in a little while.

  • We will not spend much time with applied dose and dose rate.

  • We can calculate them from potential dose and potential dose rate by applying a unitless availability factor

  • that accounts for some of the potentially- hazardous agent brought into the body not being made available.

  • Examples include some portion of an agent that may not be able to access the skin for a dermal exposure

  • or particles that are inhaled but then immediately exhaled before they can come in contact with the lining of the lungs.

  • We frequently assume that the availability factor, alpha, is equal to one, which means that the applied dose and dose rate

  • are equal to the potential dose and dose rate.

  • This is certainly not always true, but we will consider it to be true for the rest of this module.

  • The internal dose rate, then, is the availability factor times the integral from t1 to t2 of the concentration,

  • multiplied by the contact rate, times a term well refer to as the absorption factor, multiplied by the differential of time.

  • The absorption factor is the fraction of the agent that is brought into the body that is actually absorbed into the body.

  • Some of the agent may be eliminated before it can be absorbed, or it may pass through the body without being absorbed.

  • Frequently, we say that the internal dose is equal to the potential dose times an average absorption factor.

  • Similarly, we set the internal dose rate equal to the potential dose rate times the absorption factor.

  • This assumes, again, that the availability factor is equal to one.

  • Any of these doses or dose rates can be normalized by body mass.

  • We take the potential dose or dose rate, or the internal dose and dose rate,

  • and divide by the body mass to get mass- normalized doses and dose rates.

  • Let’s look at a couple of examples of these calculations.

  • In this first example, we will say that there is a Pesticide X that is released into a room at a kennel to kill fleas on a regular basis and is,

  • therefore, in the air all the time. We want to know the inhalation exposure to Pesticide X for a worker in that room.

  • Well assume that the worker weighs 50 kg and that Pesticide X is absorbed through the lungs at an average rate of 75%.

  • We've made a measurement that indicates that the air in the room contains a constant

  • Pesticide X concentration of 0.1 milligram per cubic meter.

  • The worker will spend 8 hours per day in the room and she breathes at a rate 18 cubic meters of air per day while she is working.

  • The two questions are, "What is the exposure concentration?"

  • and "What are the potential and internal and mass-normalized potential and internal dose rates to Pesticide X for this worker?"

  • So, what is the exposure concentration? Well, were given the exposure concentration in the problem statement!

  • The average concentration is equal to 0.1 milligram per cubic meter. We can multiply that by 1,000 micrograms per milligram

  • and say that the exposure concentration is also 100 micrograms per cubic meter.

  • For the second part, what are the potential and internal and mass-normalized potential

  • and internal dose rates of the pesticide for the worker?

  • Potential dose rate is equal to the average concentration times the breathing rate times the duration of exposure divided by the elapsed time

  • We know that the average concentration is 100 micrograms per cubic meter. We're given a breathing rate of 18 cubic meters per day.

  • The duration of exposure during each workday is 8 hours. The elapsed time, in this case, is one day.

  • We need to multiply one day in the denominator by 24 hours per day to be able to cancel units.

  • If we perform the calculation, we get a potential dose rate of 600 micrograms per day, on each workday.

  • The internal dose rate is equal to the potential dose rate times the absorption factor, which is 75% or 0.75.

  • So, we take 600 micrograms per day, multiply it by 0.75, and we get 450 micrograms per day.

  • The mass-normalized potential dose rate is equal to the potential dose rate divided by the body mass.

  • That is 600 micrograms per day divided by 50 kilograms, which equals 12 micrograms per kilogram per day.

  • Finally, the mass-normalized internal dose rate is equal to the internal dose rate divided by mass, which equals 450 micrograms

  • per day divided by 50 kilograms, which equals 9 micrograms per kilogram per day.

  • In a second example, we will consider a worker in a facility that produces polymer fibers.

  • This worker is exposed to an average of 7.9 milligrams per cubic meter of acrylonitrile vapor on the job.

  • He works 240 days per year, weighs 190 pounds, and breathes at a rate of about 22 liters per minute during his 8-hour workday.

  • The literature suggests that there is an absorption factor of 52% for acrylonitrile when it's inhaled.

  • The first question posed is, "What is your estimate of the worker's cumulative exposure to acrylonitrile during his 8-hour workday?"

  • The cumulative exposure can be calculated as being equal to the exposure concentration times the duration of exposure.

  • That is 7.9 milligrams per cubic meter multiplied by 8 hours, which yields a cumulative exposure of 63 milligram-hours per cubic meter.

  • The units for exposure may sound a little odd, but they take into account both the concentration and time elements of exposure.

  • For part (b), the question is, "What is your estimate of the annual internal dose rate

  • in milligrams per kilogram per year for the worker when exposed to acrylonitrile via inhalation?"

  • The internal dose rate is equal to the potential dose rate times the absorption factor divided by the body mass.

  • That is equal to the average concentration times the breathing rate multiplied by the time

  • exposed and the absorption factor divided by the time elapsed as well as the body mass.

  • Substituting values for the variables gives 7.9 milligrams per cubic meter multiplied by 22 liters per minute.

  • The time exposed is 240 days during each one year, which is the elapsed time, multiplied by 8 hours per day.

  • The absorption factor's 0.52, and the body mass of 190 pounds. Units conversions are needed,

  • so we divide by 1,000 liters per cubic meter, multiply by 60 minutes per hour, and also by 2.2 pounds per kilogram.

  • When we carry out the calculation, we get a mass-normalized internal dose rate of 120 milligrams per kilogram per year.

  • To summarize, occupational hygiene is the science, and to some extent the art,

  • of anticipating, recognizing, evaluating, and controlling workplace hazards.

  • This is also referred to as the occupational hygiene framework. Workers face a variety of chemical, physical, biological, injury,

  • and social/behavioral hazards at work, and workers are the experts on their own work environment.

  • We need to talk to them if we are going to try to understand the hazards that they face.

  • Many hazards can be evaluated using measurements or modeling, and by comparison to occupational exposure limits.

  • Options for managing those exposures or controlling them are selected based on a

  • hierarchy in which options that place the least burden on individual workers are preferred.

  • Exposure can be defined as the amount or intensity of an agent at the interface between a

  • person and his environment over a certain time interval, and dose is the amount of the agent brought into a person over a time interval.

  • This lesson was created by the Midwest Emerging Technologies Public Health and

  • Safety Training Program, or METPHAST Program, which is a collaboration among the

  • University of Minnesota School of Public Health, the University of Iowa College of Public Health, and Dakota County Technical College.

  • The METPHAST Program is funded by the National Institute of Environmental Health Sciences.

  • This module's content is solely the responsibility of its developers and does not necessarily

  • represent the official views of the National Institutes of Health.

  • Thank you for viewing this module!

Hello. Welcome to "Occupational Hygiene Principles". My name is Pete Raynor.

字幕と単語

ワンタップで英和辞典検索 単語をクリックすると、意味が表示されます

B1 中級

モジュール 1: 労働衛生の原則 (Module 1: Occupational Hygiene Principles)

  • 133 5
    kuoyumei に公開 2021 年 01 月 14 日
動画の中の単語