Assessing Health Risks Of Chemicals
The assessment of health risks from hazardous chemicals involves gaining an understanding of the situations where people can be exposed to, or come into contact with the chemicals, including the extent of exposure and how often this can occur. Health risk depends on hazard severity and level of exposure, and thus depends on both the type of chemical and also the nature of the work itself.
As with all risk assessments, the assessment involving chemical hazards needs to consider all workers potentially at risk, including those not directly involved in a work activity, as well as other people such as visitors to the workplace.
THE ROUTES OF ENTRY BY WHICH THE CHEMICAL CAN AFFECT YOUR HEALTH
The type of hazard (for example, hazard classifications of carcinogenicity, sensitisation, acute toxicity) and relevant routes of exposure (for example, inhalation, ingestion, skin contact) should be known from the hazard identification step. These are needed in the risk assessment to understand the level of risk from likely or potential exposure scenarios in your workplace.
For particulates in the air, the primary health concern effects on the lungs due to inhalation exposure. For example, crystalline silica is considered hazardous principally because of the long-term, irreversible lung effects (such as silicosis), that may arise from prolonged or repeated exposure to excessive concentrations.
Its hazardous properties are associated with inhalation, so the evaluation of risk should be based on the potential for breathing in the crystalline silica dust rather than other routes of exposure (for example, contact with the skin). In the case of crystalline silica, it is the respirable fraction of the dust that presents the greatest risk to workers as this fraction contains the smallest particles which can reach further into the lungs causing the most damage.
In contrast, even brief exposures to high concentrations of sodium hydroxide may lead to immediate effects which include irritation and burning of the skin, eyes and respiratory tract and blindness. Its hazardous properties relate to exposure via skin or eye contact and inhalation. Evaluation of risks to health for sodium hydroxide (caustic soda) should, therefore, consider the potential exposure through all of these routes.
Some chemicals may exhibit ototoxic effects. That is, they may cause hearing loss or exacerbate the effects of noise. Evaluating the use of these chemicals should be carried out in conjunction with the Code of Practice: Managing Noise and Preventing Hearing Loss at Work.
THE PHYSICAL FORM AND CONCENTRATION
Some substances may be virtually harmless in some forms (such as a block of metal, a piece of wood or granulated solid chemicals) but may be very hazardous in another form (such as fine dust particles or fume that can be readily inhaled or solutions that may be splashed and readily absorbed through skin). This is also an important consideration in assessing risks from physicochemical hazards.
The concentration of hazardous ingredients is also an important factor in the overall risk. Concentrates or pure substances may be extremely hazardous, while dilute solutions of the same chemical may not be hazardous at all.
THE CHEMICAL AND PHYSICAL PROPERTIES OF THE SUBSTANCE
Gases or liquids with low boiling points or high vapour pressures can give rise to high airborne concentrations in most circumstances, whereas high boiling point liquids such as oils are only likely to create a hazardous airborne concentration if they are heated or sprayed. Chemicals with a very low or high pH (for instance, acids and caustics respectively) are corrosive to the skin and eyes.
Some substances give off distinctive odours which can alert workers to the presence of a hazardous chemical. For example, hydrogen cyanide has a smell of bitter almonds. However, not everyone can smell hydrogen cyanide and higher concentrations of hydrogen cyanide can also overload nasal receptors resulting in workers being unable to detect it. Hazardous chemicals can also have no odour. Thus, odour should not be relied on as a means of detecting the presence of the hazardous chemical.
The chemical and physical properties are also important in assessing risks from physicochemical hazards, described later in this chapter.
DETERMINING WHO COULD BE EXPOSED, AND WHEN THIS COULD OCCUR
Workers can come in contact with a hazardous chemical and any waste, intermediate or product generated from the use of the substance if they:
- work with it directly
- are in the vicinity of where it is used or likely to be generated
- enter an enclosed space where it might be present
- disturb deposits of the substance on surfaces (for example, during cleaning) and make them airborne
- come into contact with contaminated surfaces.
You should consider all people at the workplace, including those who may not be directly involved in using, handling, storing or generating a hazardous chemical, such as:
- ancillary or support/services workers (be aware that cleaners, maintenance and laboratory staff are often exposed to both the hazardous chemicals they use in the course of their work, such as cleaning products and the hazardous chemicals used in the workplace by other workers)
- supervisors and managers.
You Should Consider:
- how specific tasks or processes are actually carried out in the workplace (for example, decanting, spraying, heating). By observing and consulting workers you can find out if they are not adhering strictly to standard procedures or if procedures are not adequately providing protection to workers.
- the quantity of the chemicals being used. Use of larger quantities could result in greater potential for exposure
- the risk controls in place and their effectiveness. For example, a ventilation system may be in use but when poorly designed, installed or maintained it may not achieve the correct level of protection (such as if filters are not regularly cleaned),
- whether each worker’s work technique has a significant bearing on their level of exposure – poor techniques can lead to greater exposure
- workers who may be working alone with hazardous chemicals and if any additional precautions or checks may be necessary in case they become incapacitated.
HOW OFTEN IS EXPOSURE LIKELY TO OCCUR AND FOR HOW LONG?
The total dose (amount) of a hazardous chemical a worker is likely to receive increases with an increase in the duration or frequency of exposure.
Estimations of the duration and frequency of exposure can be based on observation, knowledge and experience of the work. Seek information from your workers and their health and safety representatives to find out:
- Which work activities involve routine and frequent exposure to hazardous chemicals (for example, daily exposure, including during end of shift cleaning) and who are the people performing these activities?
- What happens when non-routine work, production of one-off items or isolated batches, trials, maintenance or repair operations are performed?
- What happens when there are changes to working practices in events such as cleaning, breakdowns, changes in the volume of production, adverse weather conditions?
- Are there differences between workers within a group? Anyone whose work habits or personal hygiene (for example, washing before eating, drinking or smoking) are significantly different should be considered separately.
WHAT IS THE ESTIMATED EXPOSURE TO HAZARDOUS CHEMICAL?
Once you have investigated the hazardous chemicals, the quantities used, the frequency and duration of exposure, the effectiveness of the controls already in place, and whether workers are working directly with the substance this information should then be used to estimate the level of exposure.
Inhalation exposure can be determined by personal sampling. Information on the level of airborne concentrations of chemicals can also be obtained from static area sampling, however, this method is not acceptable for determining compliance with exposure standards.
Air monitoring should be carried out by a person such as an occupational hygienist with skills to carry out the monitoring according to the appropriate standard and to interpret the results. Results from air monitoring indicate how effective your workplace controls are, for example, whether ventilation systems are operating as intended. Records of air monitoring for airborne contaminants with exposure standards must be kept for a minimum of 30 years and must be available to workers who are exposed.
An estimation of the amount of exposure to hazardous chemicals can sometimes be obtained by observation. For example, you might look for evidence of fine deposits on people and surfaces, or the presence of dust, mists or fumes visible in the air (for example, in light beams) or the presence of odours.
An indication of the airborne concentrations of hazardous chemicals can often be obtained by simple tests, such as indicator tubes or dust lamps. However, in most cases, the amount of exposure may vary throughout the day, so such tests may not establish workers’ exposure with confidence and it will be necessary to undertake detailed air monitoring. For chemicals that present a very high hazard, such as carcinogens, mutagens and reproductive toxicants, you should consider undertaking air monitoring to determine the level of exposure.
COMPLYING WITH EXPOSURE STANDARDS
As described in Section 1.5 of this Code, you must ensure that no person at the workplace is exposed to a substance or mixture in an airborne concentration that exceeds the exposure standard for the substance or mixture. Air monitoring may be necessary to ensure that workers are not exposed to airborne concentrations above the chemical’s exposure standard.
Some chemicals with exposure standards can also be absorbed through the skin – these are given a notation of ‘Sk’ in the publication Workplace Exposure Standards for Airborne Contaminants.
Biological monitoring may be a helpful means of assessing a workers’ overall exposure to a hazardous chemical that can be absorbed through the skin as well as inhaled.
Where results of monitoring show concentrations of airborne contaminants approaching or exceeding the exposure standard, you should review your control measures. Even if monitoring indicates that exposure is below an exposure standard, sensitive workers may still be at risk.
Exposure standards do not represent a ‘no-effect’ level which makes an exposure at that level safe for all workers, therefore you should ensure that exposure to any hazardous chemical is kept as low reasonably practicable. This includes exposure to hazardous chemicals that do not have exposure standards.
Some chemicals, such as isocyanates, are known to be sensitisers and can induce an adverse reaction in workers at levels well below the exposure standard once sensitisation has occurred. If a worker becomes sensitised to a chemical, the exposure standard for that chemical is no longer relevant and control measures such as improving engineering controls or job rotation to remove the affected worker from potential exposure to the chemical should be implemented.
For more information on how to interpret exposure standards and comply with the WHS Regulations, refer to Safe Work Australia’s Workplace Exposure Standards for Airborne Contaminants and Guidance on the Interpretation of Workplace Exposure Standards for Airborne Contaminants.