The probability of developing a cancer is directly related to the exposure level to that carcinogen – the greater the exposure level, the higher the chances of developing a cancer and the reverse is true as well.
Exposure to carcinogens should be completely eradicated or reduced to the lowest possible level. There are two categories of carcinogens as follows:
- Category 1: Known or presumed human carcinogens
- Category 2: Suspected human carcinogens
These categories can further be subdivided into:
- Category 1A: Known to have carcinogenic potential for humans
There is enough proof to establish a connection between human exposure to these chemicals and the incidence of cancer. In situations where it is not possible to replace carcinogens with other less harmful chemicals, the usage of carcinogens should be decreased to the lowest standard possible and personnel protective equipment can be necessary in some cases.
- Category 1B: Presumed to have carcinogenic potential for humans
These chemicals are believed to have carcinogenic potential and based on animal studies and epidemiological evidence, there is enough proof of a link between human exposure to these chemicals and the incidence of cancer.
It is advisable to consider these chemicals as carcinogens and limit their usage to the lowest standard possible. Engineering controls, sound work practices and personal protective equipment can be used. To ensure controls, routine air monitoring program must be applied and health monitoring might be necessary in some situations.
- Category 2: Suspected carcinogens
These are chemicals that are doubted to have carcinogens effects on human but there is not enough evidence as of yet to place it in Category 1. As in future research there can be a chance that these are carcinogenic, exposure to these must be kept as low as possible.
Some sensitizers such as wood dust and formaldehyde can trigger a specific immune reaction called ‘sensitisation’ in some people. Sensitisation may be displayed through skin rash or inflammation and in some people with asthmatic condition, this reaction can be very serious. People who are identified as being sensitised to a particular chemical should not be allowed to be exposed to that chemical anymore.
1.3 Ototoxic chemicals
Hearing loss can occur due to exposure to chemicals known as ototoxic substances. There are more chances of having a hearing loss if a worker is exposed to both noise and ototoxic substances compared to being exposed to either one alone. Some of the substances include toluene, xylene, lead and manganese. It is recommended to conduct regular audiometric tests where workers are exposed to ototoxic substances where the air borne exposure is greater than the workplace exposure for that substance irrespective to the noise level or where noise is greater than 80 dB(A) and any level of ototoxic substance.
Some work activities that include both ototoxic substances and noise are boat building, construction, furniture making, fueling vehicles and aircraft, fire fighting and so on.
Neurotoxins attacks tissues and cells of the body’s central nervous system and the effects can be either acute or chronic but mostly irreversible. Continued exposure to low levels of neurotoxins can give rise to chronic effects due to the degeneration of components in the nervous system.
Eyes, skin and mucous membranes or multiple parts of the body simultaneously can be affected by an irritant. A peak limitation is implemented when an exposure standard has been set based on the effects of irritation.
1.6 Systemic toxicity
When a chemical that is absorbed into the bloodstream has either acute or chronic effects on the body, this is called systemic toxicity. This can occur via inhalation, absorption through skin or ingestion and a substance can involve more than one health effect. For instance, acute intoxication or liver cirrhosis may occur due to exposure to alcohol.
1.7 Ocular effects
Some chemicals such as acids, alkalis, solvents and detergents, when in contact with the eyes, can cause ocular damage. This can range from eye irritation to ocular disturbances to serious eye damage. Acids and predominantly alkalis, can cause permanent damage for example, opacity of the eye.
1.8 Simple asphyxiants
These are non-toxic gases that can cause a decrease in oxygen concentration by displacement or dilution if present in high concentrations. It is not recommended to establish an exposure standard for simple asphyxiants but it is essential to maintain sufficient oxygen concentration.
The oxygen content in air should be at least 19.5 percent by volume under normal pressure. Since most asphyxiants are odourless, there is not enough sensory warning when the atmosphere is deficient in oxygen and unconsciousness and death can rapidly follow in these contexts. A significant number of deaths have been recorded among inadequately protected workers entering confined spaces or tanks that were not vented or gas-tested enough.
Some asphyxiants can cause an explosion hazard as well and therefore controlling the concentration of these asphyxiants should be considered. These can include ethane, ethylene, hydrogen, methane and others. Conversely, some other asphyxiants are not flammable and do not pose an explosion threat such as argon, helium and nitrogen.
Carbon dioxide is the most common asphyxiant and it does not warn about its presence even in high concentrations. It can entail toxic effects at concentrations which do not cause asphyxiation.
In the case of carbon monoxide, there should be a control in the short term exposure above the 8 TWA exposure standard for example at a concentration of 200 ppm, the total exposure should be limited to no more than 15 minutes. These controls are based on the toxicokinetic properties of carbon monoxide.
1.9 Airborne particulates
Based on their physical properties, airborne contaminants can be categorized into gases, vapours or particulate matter. Air particulates are made up of discrete particles that can be further subdivided into dusts, fumes, smokes and mists depending on the particle’s nature and size. Many factors can determine the degree of hazard linked to a particular airborne particulate. Some of these are type of particulate and its biological effect, the concentration of airborne particulate in the breathing zone of a worker and duration of exposure.
Different sizes of particles are present in most workplaces. The nature and size of the particle plays an important role in the behaviour, degree of penetration, deposition and fate of a particle after entering the respiratory system. However only a fraction of the total quantity of dust is inhaled by a worker in this breathing zone and this is known as the ínhalable fraction’. Large particles which are inhaled get deposited in the nose, pharynx and larynx while smaller ones can enter the tracheobronchial tree or even reach further into the alveolar region where gaseous exchange takes place.
This related to the particles entering mouth and nose during normal breathing and can get deposited in the respiratory tract. It applies to both toxic and non-toxic dusts. Toxic dusts have an exposure standard depending on the substance.
Inhalable fraction of dust entering the respiratory tract is divided into respirable and non-respirable fraction. Very fine dust are present in the respirable fraction that can potentially reach the lower bronchioles and alveolar regions of the lung. A size selective device is used to measure the respirable dust.
Exposure standard of dust not otherwise classified (Nuisance dusts)
Exposure standards are not assigned to all dusts however it should not be mistaken that these dusts do not pose a health hazard. Unwanted deposition of dust can occur in eyes, ears and upper respiratory tract due to very high concentrations of dust in the workplace. Cleaning procedures required for dust removal can cause injury to skin or mucous membrane.
When a substance is of low toxicity or free from toxic impurities, the exposure should be maintained below 10 g/cm3 and measured as inhalable dust.
Refined Petroleum Solvents and Mixtures
Different petroleum products can have different toxicological properties. If toxic components are present, it is compulsory to determine the concentration of each toxic components because it will be mostly the proportion of these components that will indicate if exposure standards have been surpassed.
Mineral Oil Additives
8 TWA exposure standard for oil mist of 5 mg/cm3 relates to oil mists from refined mineral oils. Most of these mineral oils contain additives to enhance their properties such as antioxidants, dispersants, emulsifiers and rust-resisting agents.
Fumes and Gases
Fumes and gases from welding and cutting activities can contain several contaminants. The airborne concentration toxic metals and toxic gases should be investigated during these processes.
Thermal Decomposition Products – Plastics
Most plastic generate toxic vapours at the normal melt processing temperatures usually below their exposure standards. Nonetheless, sensory irritation can occur by irritant aerosols and gases released.
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