SHS972 – Assignment 1

Question 1:

Workplace exposure standards in Australia are currently recognised by Safe Work Australia (SWA). Safe Work Australia was formerly identified as:

• The Australian Safety and Compensation Council (ASCC), 2005-2009
• The National Occupational Health and Safety Commission (NOHSC), 1985-
2005

NOHSC was initially assigned the task of assessing and setting workplace exposure limits for Australia. The exposure database NOHSC employed was originally obtained from:

• The American Conference of Industrial Hygienists (ACGIH)
• The United Kingdom Health and Safety Executive (HSE)

The initial exposure limits were acquired from these organisations because of the wealth of experience and research that both America and the UK had with occupational exposures. The ACGIH specified exposure limits as Threshold Limit Values (TLV). These values were derived from animal and human research as well as industry knowledge and epidemiology.

Safe Work Australia creates exposure standards based on a range of information from work health and safety statistics to continuing formal research on exposures to substances found in the workplace. A significant increase in harmful health effects from a specific substance through statistical analysis prompts SWA to assess the current exposure limit to determine whether it needs to be controlled to protect the workforce. Proposed exposure limit changes are then put out into the community for feedback.

Exposure Standards listed under the NOHSC Adopted National Exposure Standards for Atmospheric Contaminants in the Occupational Environment (NOHSC: 1003, 1995) are then used as the limits for exposures in the workplace.

Where the government determines there to be a significant risk to workers, exposure limits are drawn up into legislation such as Acts and Regulations. This can be specific such as the case of lead which has an exposure limit of 1.45 μmol / L (30μg / dL) detailed in part 7.2 of the Model Work Health and Safety Regulations 2011. Exposure limits may also be called up into legislation through standards such as the Adopted National Exposure Standards for Atmospheric Contaminants in the Occupational Environment (NOHSC: 1003, 1995) which is also referred to in chapter 7 of the Regulations 2011.

Question 2: Part A

Dusts in the workplace may have negative effects on the health of workers if inhaled. These dusts range in size from 1μm to 100μm in diameter (Tillman, 2007). ISO 7708:1995 details the three size fractions of dust for health related sampling which are:

• Inhalable fractions: Inhalable fractions have an aerodynamic diameter of less than 100μm. Inhalable dust is airborne material that enters through the nose or mouth and deposits in the respiratory tract.

• Thoracic fractions: Thoracic fractions have an aerodynamic diameter of less than 10μm. This fraction has the ability to enter through the nose and throat and deposit in the respiratory tract and parts of the lungs such as the bronchi.
• Respirable fractions: Respirable fractions have an aerodynamic diameter of less than 5μm. Respirable dust has the ability to penetrate deep into the lungs where gas exchange takes place. As such, respirable dust also has the ability to enter the blood stream through the lungs.

The size of a dust particle depends on the type of material and work process being used.
In terms of health effects, dusts are usually classified as inhalable and respirable for measurement purposes in the workplace. Thoracic fractions are covered by the inhalable fraction.

Inhalable dusts with a large diameter (up to 100μm) deposit in the throat, nose and upper airway. Inhalable dusts can irritate these structures in the airway or have immediate toxic effects. During the past thirty years, wood work has been recognized as a source of respiratory diseases (Monier, Hemery, Demoly, and Dhivert- Donnadieu, 2008). Wood dust is an inhalable dust which can cause adverse health effects in workers including bronchitis, asthma or impaired lung function (Skovsted, Schlünssen, Schaumburg, Wang and Skov, 2000). Due to their larger size, wood dust the particles rarely enter the gas exchange areas of the lung.

The respirable fraction of dust particles are deposited in the gas exchange area of the lungs including the alveoli. Respirable dust particles are associated with chronic and serious health effects. Respirable dust diseases often do not present any instantaneous symptoms and are often the result of exposure over extensive periods of time. Silicosis is an example of respirable lung disease from dust particles below 5μm in size. The hazard profile of respirable crystalline silica dust is similar to other respirable minerals such as asbestos (Busnick, 2011).Silicosis can cause a range of lung diseases including bronchitis, emphysema, chronic obstructive pulmonary disease and silicosis (Busnick, 2011). Silicosis is also a recognized human carcinogen with prolonged exposure.

Question 2: Part B

Reference to Australian Standards is made to determine monitoring methods and equipment used when quantifying personal exposure to both respirable and inhalable dust fractions. The two standards discussed include:

• AS 2985:2009 Workplace atmospheres – Method for sampling and gravimetric determination of respirable dust
• AS 3640:2009 Workplace atmospheres – Method for sampling and gravimetric determination of inhalable dust

These standards provide a method of assessing personal exposure to respirable and inhalable dust via sampling a workers breathing zone. The breathing zone relates to a 300mm radius in the front of the face and measured from the mid-point of a line joining the ear. All sampling equipment should be calibrated prior to use for effective measurements. All samples should also be sent to a NATA certified laboratory for accuracy and consistency.

Respirable dust

The sampling system equipment required for monitoring respirable dust in the workplace include a filter, where the sample is collected, a size-selective sampler and a pump to pass the air through the filter. With personal sampling instrumentation, the filter is located within the breathing zone and connected to a pump via flexible tubing. A size selective sampling miniature cyclone which conforms to the sampling efficiency curve such as a BCIRA (British Cast Iron Research Association) is necessary for sampling respirable dusts.
Filter sizes of 25mm diameter are ideal however a filter with 37mm diameter can also be used, however the filter should be chosen to suit the sampling head. Pore sizes for filters should be 5μm or less and should be chosen so that electrostatic charge, moisture variations and loss of filter or sample do not drastically influence analysis. Transportation of the filters should also be undertaken carefully to avoid sample loss. Sampling pumps should allow for operation at the flow rate of ±0.1L/min for the entire duration of the sampling time frame. The pulsation rate should range between 0.1 and 0.2 L/min.

Sampling time frames should run for as long as practicable and will be set at 8 hours, allowing for individual exposure of individuals. The sampling procedure will occur as follows:

1. Turn the pump on and record information on size-selective sampling number, filter and pump identification, date and pump start time, initial flow rate, secondary flow rate used and workers identification with description of static location.
2. Attach sampling pump to the worker
3. Fasten sampling device with pre-weighed filter to worker within the breathing zone. Ensure all tubing is free from leaks and kinks.
4. When sampling note the tasks being performed, risk control measures in place and any other relevant data. Prior to turning pump off, record the time and re-measure and record the flow rate through the sampling device.
5. If flow rate variation more than ±5% occurs, the sample is invalid.
6. Sample device or cassette will be placed in a pre-labelled, dust free container.
7. Allow filter equilibrium overnight then apply routine weigh checks with samples and blank filters and record weights in milligrams.

Inhalable dust

The sampling system equipment required for monitoring inhalable dust in the workplace include a filter, where the sample is collected, a size-selective sampler and a pump to pass the air through the filter. With personal sampling instrumentation, the filter is located within the breathing zone and connected to a pump via flexible tubing.

The IOM inhalable dust sampling head developed by the UK Institute of Occupational Medicine in Edinburgh is a single orifice entry and a filter contained within a special cassette. This unit requires a pump capable of maintaining a smooth flow rate of 2.0 ±0.2 L/min for the entire duration of the sampling time frame.

Sampling time frames should run for as long as practicable and will be set at 8 hours, allowing for individual exposure of individuals. The sampling procedure will occur as follows:

1. Turn the pump on and record information on sampling device number, filter and pump identification, date and pump start time, initial flow rate, secondary flow rate used and workers identification with description of static location.
2. Attach sampling pump to the worker
3. Fasten sampling device with pre-weighed filter to worker within the breathing zone. Ensure all tubing is free from leaks and kinks.
4. When sampling note the tasks being performed, risk control measures in place and any other relevant data. Prior to turning pump off, record the time and re-measure and record the flow rate through the sampling device.
5. If flow rate variation more than ±10% occurs, the sample is invalid.
6. Sample device or cassette will be placed in a pre-labelled, dust free container.
7. Allow filter equilibrium overnight then apply routine weigh checks with samples and blank filters and record weights in milligrams.

Question 3: Part A

Construction workers are ex¬posed to hazardous dust when using handheld electric grind¬ers to smooth poured con¬crete surfaces. Respirable crystalline silica dust has been responsible for a significant number of adverse occupational health effects. There have been numerous documented cases of occupational deaths from silicosis, a disease which results in the formation of scar tissue in the lung (AIOH, 2009).

In Australia, Hazardous Substances Information System (HSIS) and NOHSC (1995) details the occupational exposure of 0.1 mg/m3 TWA for respirable crystalline silica. This exposure limit is critical in identifying whether workers are exposed to levels of silica dust which may have an adverse effect on their health. Identifying the need for exposure measurements can be achieved by (NIOSH, 1977):

• workplace material surveys
• workplace observations
• analysis of employee complaints or symptoms
• occupational environmental reports

In identifying the need for exposure measurements it is important to establish similar exposure groups. Splitting the workforce into similar exposure groups assists in the accurate identification of exposure levels. It can also reduce the cost of the program by sampling within exposure groups. Splitting workers into high risk groups such as process operators, and low risk groups such as administration, ensures a control group for the monitoring program.

Question 3: Part B

To protect the health of employees, exposure measurements to silica dust should be unbiased and representative samples of total employee exposure (NIOSH, 1977). As such, statistically based monitoring programs provide the best use of exposure measurement resources and ensure efficient sampling strategies and evaluation of measurement data.

The Occupational Exposure Sampling Strategy Manual (1977) identifies three key elements in the development of a statistically based monitoring program:

• Determining the need for exposure measurements
• Exposure measurement sampling strategy
• Statistical analysis of exposure measurement results

Identifying the need for exposure measurements can be achieved by (NIOSH, 1977):

• workplace material surveys
• workplace observations
• analysis of employee complaints or symptoms
• occupational environmental reports

In identifying the need for exposure measurements it is important to determine similar exposure groups. Dividing the workforce into similar exposure groups assists in the accurate identification of exposure levels. It can also reduce the cost of the program by sampling within exposure groups. Furthermore, splitting workers into high risk groups such as manual concrete surface grinders, and low risk groups such as administration, ensures that there is a control group for the monitoring program.

Exposure measurement sampling strategy

The selection of employees to be sampled is important when developing a statistically based monitoring programme. NIOSH (1977) details the number of samples required for different group sizes for 95% confidence. For example, if the exposure groups were divided into two high risk manual concrete surface grinder groups containing 40 employees each then the required sample size would be 17 from each group. If a control/administrative group consisted of 23 employees, then the required sample size would be 14. By using the sampling guidelines specified by NIOSH, the costs of the program are minimised while retaining the integrity of the sampling program.

Samples taken should adhere to the following specific requirements for crystalline silica dust (Kaelin and Liang, 2008).

• Sample pump flow rate of 2 litres per minute that is evaluated before and after each use
• The use of a 10 mm cyclone air sampling device and pre-weighted 37mm cassette
• A process for cleaning and monthly leak testing of the cyclone using a pressure gage
• Samples should be taken within the breathing zone of the employee
• All samples should be assessed by a NATA accredited laboratory

The sampling measurement should be taken according to the following methods listed in order of precision and accuracy (NIOSH, 1977).

1. Full period consecutive samples measurement
2. Full period single sample measurement
3. Partial period consecutive samples measurement
4. Grab samples measurement

Assuming that the most robust monitoring program is required, the full period consecutive samples measurement should be used. This method is the best in that it yields the narrowest confidence limits which results in statistical benefits (NIOSH, 1977).

Statistical analysis of exposure measurement results

Exposure measurement results should be analysed with exposure limits in mind. For silica dust, employee exposures greater than 0.1 mg/m3 over an 8 hour working day suggest that adverse health effects may be occurring. Samples with a confidence interval rating of 95% give an accurate measurement of exposure to, in this case, silica dust. If workers have been identified as being exposed to silica dust above the exposure limit then controls are required to eliminate or reduce the risk to workers.

The program should also incorporate repeat sampling of the exposure groups. This should occur when there are any changes to the workplace, work practices or process. If the workplace environment remains static, then sampling should occur at least every 2 months for workers below the exposure limit and once a month for workers above the exposure limit (NIOSH, 1977). Testing may occur more frequently based on professional judgment.

Question 3: Part C

In terms of controls for the manual concrete surface grinding, the first step should be to identify whether it is feasible and practical to modify or replace the current process. This includes eliminating or substituting the products, the grinding process, or changing the equipment and technology used in the process. Given the nature of crystalline silica and it’s presence within the working area, elimination or substitution as control measures are generally unrealistic.

To reduce exposures the remaining controls of engineering, administration and the use of PPE should be implemented. The practicality and costs of implementing these controls needs to be determined against the expected gain in health benefits. Research indicates that these control measures have been effective in reducing silicosis incidents. The historical reduction in silicosis numbers is due to a combination of regular medical surveillance, reduction in exposures such as compliance with a regulatory exposure standard, the prohibition of specific tasks associated with high risk (such as sand blasting and the use of silica flour in foundry operations) and the use of adequate dust suppression systems such as ventilation and wetting down, (AIOH 2009).

The control principles that apply to crystalline silica are similar to those that apply to all mechanically generated dust exposures, (Akbar-Khanzadeh et al, 2007). The following controls are recommended for implementation when performing manual concrete surface grinding:

• Design and implement processes and activities to minimise emission, release and spread of crystalline silica dust
• Position personnel so they are kept away from the dust either in enclosed and filtered cabins and in the opposite direction of the draft of dust emission
• Use sharp cutting tools that minimise the generation of large quantities of dust
• Use wet processes to prevent crystalline silica dust generation
• Use water suppression to prevent the spread of crystalline silica dust
• Use ventilation, either dilution or extraction, to control dust spread and release
• Apply good house-keeping practices to prevent crystalline silica dust build-up
• Provide training in the health effects of crystalline silica dust and its control
• Where control of exposure cannot be achieved, provision of suitable PPE in combination with other control measures is recommended. For most exposures to crystalline silica this will be a P1 or P2 half face respirator. Training in the use and limitations of respiratory protective equipment (eg ensure a clean shaven face) and face fit testing is also recommended, as per AS 1715 (2009).

References:

Akbar-Khanzadeh, F, Milz, S, Ames, A, Susi, PP, Bisesi, M, Khuder, SA, Akbar-Khanzadeh, M 2007, ‘Crystalline silica dust and respirable particulate matter during indoor concrete grinding – wet grinding and ventilated grinding compared with uncontrolled conventional grinding’, Journal of Occupational and Environmental Hygiene, no. 4, p. 770-779.

AIOH Exposure Standards Committee 2009, ‘AIOH Position Paper: Respirable Crystalline Silica and Occupational Health Issues’, Tullamarine, Victoria, Australia.

American Conference of Governmental Industrial Hygienists (ACGIH), ‘TLV Resources’ http://www.acgih.org/home.htm.

AS/NZS1715:2009 -Selection, use and maintenance of respiratory protective equipment, accessed 16 September 2012.

AS2985:2009 - Workplace atmospheres -Method for sampling and gravimetric determination of respirable dust, accessed 16 September 2012.

AS3640:2009 - Workplace atmospheres - Method for sampling and gravimetric determination of inhalable dust, accessed via UOW library, 16 September 2012.

Busick, J 2011, ‘Crystallizing General Industry's Approach to Crystalline Silica’, Safety Compliance Letter, no. 2528, p. 5.

Health and Safety Executive (HSE) 2005, ‘EH40/2005 Workplace exposure limits’, http://www.hse.gov.uk/coshh/table1.pdf

ISO 7708:1995(E) Air quality—Particle size fraction definitions for health-related sampling, accessed 16 September 2012.

Kaelin, AB and Liang, S 2008, ‘New OSHA program targets silica, other blast cleaning chemicals’, Journal of Protective Coatings & Linings, p. 47, accessed 17 September 2012.

Monier, S, Hemery, M, Demoly, P, and Dhivert-Donnadieu, H 2008, ‘Occupational asthma to wood dust’, Revue Francaise D Allergologie Et D Immunologie Clinique, vol. 48, no. 1, pp. 31-34.

National Institute for Occupational Safety and Health (NIOSH) 1977, ‘Occupational
Exposure Sampling Strategy Manual’, US Department of Health, Education and
Welfare, accessed 17 September 2012.

National Occupational Health and Safety Commission (NOHSC) 1995, ‘Adopted National Exposure Standards for Atmospheric Contaminants in the Occupational Environment’, (NOHSC: 1003), accessed 16 September 2012.

SafeWork Australia website, www.safeworkaustralia.gov.au, accessed 16 September 2012.

Skovsted, TA, Schlünssen, V, Schaumburg, I, Wang, P and Skov, PS, 2000, ‘Hypersensitivity to wood dust’, Allergy, ISSN 1398-9995, 11/2000, vol. 55, no. 11, p. 1089.

Tillman, C 2007, .Principles of Occupational Health and Hygiene’, Crows Nest: Allen & Unwin.