Occupational Hygiene

That is an Environmental Health Hazard?

The first step in understanding health risks related to exposures requires the collection of “basic characterisation” information from available sources. A traditional method applied by occupational hygienists to initially survey a workplace or environment is used to determine both the types and possible exposures from hazards (such as noise, chemicals, radiation).

Environmental health addresses the assessment and control of environmental factors that can potentially affect health. It is targeted towards preventing disease, creating health-supporting environments and encouraging positive human behaviours. Our environment generally consists of physical, chemical and biological factors and our relationship with our environment is always interactive. This means that we affect our environment and our environment affects us. These interactions may expose us to environmental health hazards; that is any environmental factors or situations that can cause injury, disease or death.





The walk-through survey
The walk-through survey can be targeted or limited to particular hazards such as silica, dust, or noise, to focus attention on control of all hazards to workers. A full walk-through survey is frequently used to provide information on establishing a framework for:

- Future investigations
- Prioritising hazards
- Determining the requirements for measurement
- Establishing some immediate control of potential exposures

Other sources of basic characterisation
Information include:

- Workers interviews
- Observing exposure tasks
- Material safety data sheets
- Workforce scheduling
- Production data
- Equipment and maintenance schedules to identify potential exposure agents and
people possibly exposed.


Sources of workplace contaminants
Work processes likely to generate dust include the following:
- Mining, quarrying and tunnelling
- Stone masonry
- Construction
- Any process which breaks or separates solid material
- Foundries and other metallurgical processes, especially the cleaning of casting and
breaking of moulds
- Any process using abrasive blasting, such as removal of paint and rust, cleaning of
buildings and small objects, and etching of glass.

- Manufacture of glass and ceramics

- Handling of powdered chemicals in the chemical, pesticide, rubber manufacturing
and pharmaceutical industries

- Any process involving weighing, bagging, bag-emptying or dry transport of powdered
or friable materials.

Environmental exposure to hazards
To reduce the adverse impacts of environmental hazards on human health you need to understand where the hazard comes from, identify it and the pathway it can take to affect people.




Biological hazards
The source of the hazard is the place of origin from proposed and existing activities. Patients and carriers discharge infectious agents (biological hazards) that could infect healthy people. Industrial processes in a factory release chemical hazards that may be found in sewage; the sewage could reach drinking water, thereby creating the possibility of ingesting these chemicals. Household activities could also be sources of hazards, for example cooking with fuels such as animal dung and charcoal produces toxic smoke that can cause lung diseases.

Chemical hazards
The type of hazard is the particular chemical, infectious agent or other agent involved. The pathway is the route by which the hazard gets from the source to the person.

The response or the effect is the health outcome (changes in body function or health) after the hazard has affected the person. The amount and type of change (or response) depends on the type of hazard and the effect it can have on different people. This would depend on the person’s individual health and factors such as their age; for example, young children or people who are already sick are often more harmed by diseases such as diarrhoea than healthy adults.

If you want to prevent a hazard, you need to understand the source of the hazard:
- Where it comes from
- The type of hazard (the type and concentration of a chemical)
- The pathway (the affected environment and how the exposure could take place)
- The response (the effect the hazard could have on people)

We will demonstrate this with an example.

Sewage containing cadmium (a toxic chemical) is produced by a hide-processing factory and flows into a river. People downstream of the point of discharge drink the contaminated water and become sick. The environmental hazards exposure is described as follows:

- The source is sewage from a factory.
- The type of hazard is chemical, in this case cadmium.
- The pathway or affected environment is the river that is used by the public as a
source of drinking water and the exposure took place by swallowing / ingesting the
chemical with drinking water. In addition, any fish contaminated with cadmium may
have been eaten.
- The response is that people who consume the contaminated water and fish had
symptoms of cadmium poisoning (i.e. joint and spinal pains, pains in the abdomen)
and they complained to a health centre.

The effects of hazardous environmental conditions
There is a wide range of effects that the environment may have on human health, but it is very far from exhaustive and for the sake of conciseness many hazards or their effects have not been mentioned.

Problems to health
Problems to health arise at two levels, individual and species e.g. animals. At the level of the individual, the environmental influences which slowly ‘shape’ the species may in some respect or another cause harm to some members of the species, that is how a species evolves. At the level of the species, we must remember that the process of evolution is relatively slow when compared to the rate at which a man can bring about environmental change. This means that unless efforts are made to care for the environment, the human species may suffer to an extent that other species already have suffered.

Effects on the environment and principles
Although work provides many economic and other benefits, a wide array of workplace hazards also present risks to the health and safety of people at work. These include but are not limited to, “chemicals, biological agents, physical factors, adverse ergonomic conditions, allergens, a complex network of safety risks,” and a broad range of psychosocial risk factors.

There are four underlying principles and factors of the environment that can affect well-being in the workplace namely:

Physical hazards, and their adverse health effects
Increasing extremes of temperature, as a result of climatic change, could result in increased mortality even in temperate climates.

Important issues concerning physical hazards include those relating to health effects of electromagnetic radiation and ionising radiation. If one excludes the occupational environment, then noise and other physical hazards may present a nuisance to many inhabitants, and impair general wellbeing.

Environmental noise does not usually contribute to deafness but notable exceptions may include noisy discotheques and “personal stereos”.

Electromagnetic radiation ranges from low frequency, relatively low energy, radiation such as:
- Radio and microwaves through to infrared
- Visible light
- Ultraviolet
- X-rays
- Gamma rays.

These last as well as other forms of radioactivity such as high energy subatomic particles (such as electrons (Beta rays) can cause intracellular ionisation and are therefore called ionising radiation.

Exposure to ultraviolet (UV) radiation carries an increased risk of skin cancer such as melanoma, and of cataracts which are to an extent exposure related.

Some pollutants such as chlorofluorocarbons (CFCs) used as refrigerants or in aerosol propellants or in the manufacture of certain plastics can damage the “ozone layer” in the higher atmosphere (stratosphere) and thus allow more UV light to reach us, and harm us directly.

The average person exposed is natural in origin, and, of the manmade sources, medical diagnosis and treatment is on average the largest source to the individual. A very important issue is the extent to which radon gas arising from certain rock types beneath dwellings can contribute to cancer risk.

The explanation for leukaemia clusters around nuclear power plants is not yet resolved. Similar clustering can occur in other parts of the country. The effect of viral infections associated with population shifts may be important but requires further study.


Chemical hazards, and their adverse health effects
If one includes tobacco smoke as an environmental hazard then it probably represents the single biggest known airborne chemical risk to health, whether measured in terms of death rates or ill-health (from lung cancer, other lung diseases such as chronic bronchitis and emphysema, and disease of the heart, especially, and of blood vessels and other parts of the body). To a much lesser degree of risk, these adverse effects apply to non-smokers exposed passively to sidestream tobacco smoke.

General airborne pollution arises from a variety of causes but can usefully be subdivided into pollution from combustion or from other sources. Combustion of coal and other solid fuels can produce smoke (containing polycyclic aromatic hydrocarbons - PAH) and Sulphur dioxide besides other agents such as those also produced by:

Combustion of liquid petroleum products which can generate carbon monoxide, oxides of nitrogen and other agents. Industry and incineration can generate a wide range of products of combustion such as oxides of Sulphur and nitrogen, polycyclic aromatic hydrocarbons, dioxins etc.

Combustion of any fossil fuel generates varying amounts of particulate matter. It also adds to the environmental burden of carbon dioxide an important “greenhouse” gas but in these low concentrations it does not affect human health directly.

Combustion of fuel can also generate hazardous substances in other ways, besides by chemical oxidation, such as by liberating benzene (from the “cracking” of petrol) or lead (from leaded petrol). Some of the primary pollutants such as nitrogen dioxide can, under the influence of UV light generate secondary pollutants notably ozone (an allotrope of oxygen).

What is still unclear is the extent to which urban airborne pollution in the majority of cities complying with current air quality guidelines, contributes to ill health, i.e. whether the air quality guidelines are stringent enough, to protect all the population.

Health effects of concern are:
- Asthma
- Bronchitis
- Lung diseases

Moreover, there is increasing evidence to suggest the pollution from particulate matter at levels up till now considered “safe” is associated with an increased risk of morbidity and mortality from cardiopulmonary disease especially in people with other risk factors (such as old age, or heart and lung disease). These concerns are the subject of a great deal of research throughout the world. Although high occupational exposures to exhaust especially from diesel, and to benzene does increase the risk of some cancers, reliable direct evidence of an increased cancer risk to the population at large from the lower levels to which they are exposed is lacking.

Certain modern building materials may liberate gases or vapours such as formaldehyde at low concentration but which might provoke mild respiratory and other symptoms in some occupants. Modern building standards for asbestos in buildings are such that the resulting airborne fibre concentrations are so small as not to present any risk at all of asbestosis.




Biological hazards, and their adverse health effects
These generally fall into two broad categories, those which produce adverse effects in non-infective (allergic) ways. Those which produce adverse health effects through infection.

As regards microbiological hazards in water, substantial improvements in the health of the population have resulted historically from the supply of drinking water free from disease causing organisms such as cholera. Similar improvements can be expected in the health of the inhabitants of developing countries if microbiologically safe water is provided by avoidance of contamination, and appropriate purification including disinfection (usually by chlorination). Occasional outbreaks of waterborne infection still arise from contamination of drinking water by soiled water (usually coliforms).

There can be other opportunities for further bacteriological contamination. Thus, Legionella can grow in sumps or dead legs in the plumbing system and may then be dispersed as aerosols from showers.

Recreational water which is heavily contaminated with pathogens, notably coliform bacteria has been shown to be associated with an increased risk of gastrointestinal and other infectious illness, usually self-limiting.

So-called “clinical” waste is not merely an occupation hazard of health care workers but is becoming an increasingly more important risk, like children finding blood stained needles.

Many allergens such as grass pollen grains, or faecal material from house dust mites may cause attacks of asthma or “hay fever” (allergic rhinitis). There is evidence that high exposure to these allergens early in life, increases the risk of suffering from asthma later on. An increasing number of studies suggest that airborne chemical pollution can act synergistically with naturally occurring allergens and result in effects on lung function at concentrations lower than those at which either the allergen or chemical irritant on its own would have produced an adverse effect.

Psychosocial hazards
Psychosocial hazards include risks to the mental and emotional well-being of workers, such as feelings of job insecurity, long work hours, and poor work-life balance.

Non-chemical physical environmental factors
Non-chemical physical environmental factors refer to other outside hazards that affect the health and wellbeing of people. Some are natural causes and others not but it is not due to chemical exposure. Let us describe these different ranges.

Heat and cold
Temperature regulation centres in our brain are sensitive to small changes of blood temperature and also get feedback from sensory nerves at the skin, our brains then use this information to adjust our bodies responses to heat.

Physiological responses to heat
When exposed to heat the blood vessels in our skin expand and our pulse rate increases. This increases blood flow to the surface of the body, thus increasing the potential for heat transfer from body core to skin and surroundings. Sweating also increases heat loss due to latent heat of evaporation. This also has the added effect that it increases our water requirements.

In very hot conditions, sweating offers the greatest potential for regulating body temperature. Ongoing from a cool to a predominantly warmer climate it is necessary to allow the body to acclimatise by increasing blood volume and seat capacity while decreasing salt losses in sweat. It takes about 3 days for this acclimatization to be about 60% complete and about 10 days for complete acclimatisation. This increased sweat capacity is lost after a few days in a cooler environment.

Possible adverse effects of exposure to excessive heat include:
- Fatigue
- Behavioural modification
- Reduced concentration
- Heat cramps due to salt loss
- Fainting from heat exhaustion
- Heat stroke

Physiological responses to cold
When exposed to cold the blood vessels in our skin contract and heat flow to the body surface is reduced, thus minimising heat loss from the body. Heat production is increased by physical activity and shivering. There is no physiological acclimatisation to cold. Possible adverse effects to excessive cold include:
- Lassitude/listlessness
- Chilblains
- Frostbite
- Hypothermia

Noise
It has become common practice to define noise as unwanted sound and it has been known for many years as a cause of hearing loss in industry. So, what exactly is sound and how do we hear it? Sound is the sensation that is perceived by the human or animal brain as a result of longitudinal vibrations of molecules of the air impinging on the ear.

Sounds are actually pressure waves caused by a vibrating body, which radiate from the source. The human ear can sense and perceive small and rapid pressure waves as sound (noise) and convey information on their size (amplitude) and frequency to the brain.

The external ear, i.e. the part we can see, receives the pressure waves and passes them along the auditory canal to a membrane - the eardrum, which is situated just inside the skull for protection. The eardrum vibrates in response to the sound pressure waves and this vibration is transmitted through the 3 small bones of the middle ear malleus, incus and stapes (hammer, anvil and stirrup to another membrane, the oval window of the inner ear.

The middle ear also contains the eustachian tube, which provides an opening to the throat and so maintains the middle ear at atmospheric pressure. This pressure equalisation is necessary because the eardrum is required to respond to rapid, small fluctuations in pressure, not to absolute pressure.

The oval window in turn passes the vibrations on to the cochlea, a snail shaped organ containing liquid and some 25,000 receptive cells (nerve endings). The vibrations generate pressure waves in the liquid of the cochlea, and these stimulate the nerve endings which transmit corresponding electrical signals to the brain. Each receptive cell has its own pitch response and thus is able to analyse and separate out a mixture of incoming signals into their individual frequency components. This facility enables the human ear to identify individual notes amongst the incoming volley of sound.

Audible Sound
Two key features of sound are frequency and intensity. The number of pressure waves/vibrations per second is known as the frequency, and is expressed in the unit Hertz (Hz), the more fluctuations per second the higher the pitch of the sound.

The frequency range of the human ear is normally quoted as being between 20 Hz and 20,000Hz (20 KHz). Middle C in music is at approximately 260 Hz (musicians’’ opinions vary between 255 - 278 Hz), and doubling the frequency raises the pitch one octave, hence the octave above middle C (260 Hz) has a frequency of 520 Hz.

By intensity (I) we mean the amplitude (size of the pressure waves and is defined as the average amount of energy passing through a unit area in unit time and is expressed in watts per meter squared (Wm2).

It becomes very complicated to quote noise levels in measurements of sound pressure (Pascals) or intensity (Watts/meter 2), as the numbers are very unwieldy. We therefore relate them to a reference level (in this case, the threshold of hearing) and using a log scale for the result, a much more manageable figure can be produced. This is called the decibel which is one tenth of a Bel. The decibel (dB) has no dimensions as such; it is just a unit of comparison arranged in a logarithmic scale, so that increasing the number corresponds to a multiplication of intensity. The loudness of noise is a function of both the intensity and the frequency.

Health effects of excessive noise
It has long been known that regular exposure to high intensity noise can result in damage to the hearing mechanism, the degree of damage being proportional to the total integrated noise energy incident upon the ears. The damage is related to the intensity, nature (continuous or intermittent) and duration of the noise exposure, and has microscopically visible effects on the inner ear that are essentially irreparable and incurable. There are five possible health effects of noise:

Noise Induced Hearing Loss (NIHL) is a cumulative effect from repeated exposure. It is due to damage to the hair cells of the cochlea in the inner ear. First indication of hearing loss occurs with a reduction in the ability to hear around the 4-kHz frequency range. Over time, if the exposure continues the noise-induced hearing damage shows as an increase in the depth of the hearing loss and a wid

- Tinnitus - Noise heard in the ear without an external cause; it frequently
accompanies deafness.

- Temporary Threshold Shift (TTS) - Damage to the hair cells of the inner ear which
can impair hearing temporarily, resulting from exposure to high noise levels.
Recovery occurs once exposure to high noise levels is reduced, typically over a
period of several hours.

- Physical damage to the eardrum and ossicles induced by excessively high noises
e.g. explosions. This type of hearing loss is referred to as conductive hearing loss.

- Annoyance/stress, which is difficult to measure and quantify, but may cause
psychological effects such as poor concentration, irritability and stress.

Besides causing temporary or permanent hearing loss, noise can also be a safety hazard. Most obviously, noise interferes with verbal communication, leading to errors and failures to respond to warning sounds and shouts.

Hearing damage can be induced by continuous exposure to levels in excess of 85 dB(A) but an individual’s response varies within a population. Continuous exposure to levels in excess of 90 dB(A) will result in 20% of the exposed population suffering from NIHL.