a basic introduction to hazardous airborne contaminants.
A Basic Introduction to Hazardous Airborne Contaminants.
How dangerous are airborne contaminants?
Airborne contaminants are made up of different properties. These contaminants contain various chemicals, but more importantly possess different sized particles. Depending on the size of particle depends on how much damage will be done to the person breathing the hazardous air.
Airborne contaminants that can be inhaled directly can be classified on the basis of their physical properties either as gases, vapours or particulate matter. Airborne particulates consist of discrete particles and may be further characterised as dusts, fumes, smokes or mists, depending on the nature of the particle and its size.
Why is dust so harmful?
Most workplace dusts contain particles of widely ranging size. The behaviour, extent of penetration, deposition and fate of a particle after entry into the respiratory system, and the response it causes depend on the nature and size of the particle.
Only part of the total quantity of dust which is present in the worker’s breathing zone is inhaled. This part is called the ‘inhalable fraction’ of dust and is determined by the flow rates in the nose and mouth areas, as well as the airflow around the head.
Practically all smaller particles will be inhaled, while the number of larger particles inhaled decreases rapidly as a function of increasing aerodynamic diameter. The larger particles in the inhalable fraction of dust are deposited in the nose, pharynx and larynx.
The deposition of particles can occur during either inhalation or exhalation. Deposited particles may be transported to the digestive tract by means of the mucociliary clearing mechanism of the respiratory tract and, in some cases, subsequently absorbed into the body.
What’s the difference between inhalable dust and respirable dust?
Inhalable dust refers to the particle size entering the mouth and nose during normal breathing. These particles may be deposited in the respiratory tract. The term inhalable dust applies to both non-toxic and toxic dusts.
Inhalable dusts that are toxic have an exposure standard. Where the toxic component of the dust is measured, this is satisfactory as long as the exposure standard for dusts is not exceeded. Exposure standards for dusts are measured as inhalable dusts unless there is a notation specifying an alternate method, e.g. cotton dust, silica.
The inhalable fraction of dust entering the respiratory tract may be further divided into ‘respirable’ and ‘non- respirable’ fractions. The respirable fraction is composed of the very fine dust which is able to reach the lower bronchioles and alveolar regions of the lung.
The following substances have an exposure standard based upon the respirable dust fraction, quartz, cristobalite, tridymite, fumed silica, coal dust and soapstone.
The response of the body from exposure to substances and mixtures depends on the nature of the substance, the health effects it can cause, and the amount of the substance or mixture absorbed by the body.
Who regulates this hazard?
There are specific requirements to manage risks rising from exposure to chemicals under the WHS Regulations, including those associated with exposure standards, airborne contaminants and asbestos.
Safe Work Australia works with the Commonwealth, state and territory governments to improve work health and safety and workers’ compensation arrangements. The Commonwealth, states and territories have responsibility for regulating and enforcing work health and safety laws in their jurisdiction.
All reasonably practicable steps must be taken to eliminate or minimise exposure to a level well below the exposure standard. Sections 17 and 19 of the WHS Act require that the risks posed by exposure to substances in the workplace are eliminated or kept as low as is reasonably practicable.
For this reason, it is important the airborne concentration of a substance or mixture hazardous to health is kept low to minimise the risk to health, regardless of whether or not there is an exposure standard or what the value of the exposure standard is.
What are exposure standards?
Exposure standards are listed in the Workplace Exposure Standards for Airborne Contaminants and represents the airborne concentration of a particular substance or mixture that must not be exceeded. There are three types of exposure standard:
8-hour time-weighted average (TWA)
short term exposure limit (STEL)
An eight-hour time-weighted average exposure standards is the average airborne concentration of a particular substance permitted over an eight-hour working day and a 5-day working week.
A short term exposure limit is the time-weighted maximum average airborne concentration of a particular substance permitted over a 15 minute period.
Peak limitation exposure standards are a maximum or peak airborne concentration of a particular substance determined over the shortest analytically practicable period of time which does not exceed 15 minutes.
To conduct an effective air monitoring program requires training, specialist knowledge and a high level of competency and experience. Interpretation of the results of air monitoring and decisions about whether a workplace is complying with exposure standards can be complex.
Therefore, seeking the services of a qualified professional, who can interpret results and design a suitable air monitoring programme is highly recommended.