What is the hierarchy of controls for dust?

From 1 September , the occupational exposure limits (OEL) for respirable dust and respirable crystalline silica (RCS) are 1.5mg/m 3 and 0.05mg/m 3 respectively.

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The risk of workers being exposed to hazardous dust particles should be controlled using the hierarchy of controls shown below. Controls should focus on higher-order controls (e.g. elimination, substitution and isolation of the hazard) as the most effective means of treating the hazard.

Note: The Mining and Quarrying Safety and Health Regulation includes a specific requirement for controls to be applied in this order.

Hierarchy of controls

Hazard controls should be applied in this order:

1. Elimination&#;remove the hazard, or the need to perform the hazardous activity.
2. Substitution&#;substitute a safer alternative.
3. Separation/isolation&#;isolate or separate people from the hazard by use of barriers, distance or time.
4. Engineering controls&#;redesign or modify tools or equipment.
5. Administrative controls&#;use training, rules, procedures to reduce the risk of the hazard.
6. Personal protective equipment&#;provide fit-for-purpose protective equipment.

More than one control may need to be used to adequately control the hazard. Controls used must be maintained to ensure they continue to remain effective.

Examples of dust controls

Elimination

• Adopt production processes that generate less dust (any wet method is likely to generate less dust than a dry one).
• Treat the dust at its point of generation, as this is more effective than capturing airborne dust.
• Treat the dust on its transmission path using dust suppression techniques (e.g. water sprays, chemical additives, local exhaust ventilation (LEV), vacuum).

Substitution with a lesser hazard

• Substitute with a less hazardous substance, such as the use of pellets rather than powders, or replace sand with garnet as abrasive blasting agent.

Separation/isolation of workers from the hazard

• Place a physical barrier between the dust-generating task and the worker, such as the use of enclosed cabins to isolate workers.
• Use remotely operated machinery, such as remotely controlled conveyors.

Engineering controls

• Choose appropriate equipment (e.g. correct cutting blades for ore body).
• Replace and maintain equipment regularly to ensure cutting blades and picks remain sharp.
• Suppress dust by using water sprays on stockpiles and roads, and when using machinery and cutting equipment. Use additive in water sprays to suppress dust and adjust the droplet size of the spray according to dust particle size.
• Use enclosures (e.g. covered conveyors, enclosed cabs on vehicles, plant and equipment).
• Rehabilitate exposed mine land to reduce environmental dust load.
• Use ventilation and filtration to minimise dust (e.g. adjust ventilation rates for maximum efficiency, use local exhaust ventilation when necessary).
• Enclose cabins where possible, ensure seals are well-maintained, provide inlet air filtration for respirable particles, and use positive pressure air inside cabs to prevent dust penetration.
• Cover product conveyors.
• Cover loads for road haulage where practicable.
• Apply stone dust to underground workings.

Administrative controls

• Ensure regular maintenance and housekeeping of vehicles and mine workings.
• Position personnel away from dust-generating activity by establishing exclusion zones.
• Maintain unmade roads and ensure ground conditions throughout sites are appropriate to the machines using them.
• Provide training and information to workers on the hazards, risks and controls of dusty tasks, as well as supervision for workers.
• Limit the duration and magnitude of exposure to dust (e.g. worker rotation, job task changes).
• Ensure work schedules have adequate rest periods to limit exposure.
• Change the location of dumping operations or modify blasting programs to suit weather conditions.
• Provide adequate signage.

Personal protective equipment (PPE)

• Ensure higher-order controls are adopted before resorting to PPE.
• Select the most appropriate respiratory protection for the task (e.g. P1 or P2, full face, half face, powered air, purifying). Read AS/NZS &#; Selection, use and maintenance of respiratory protective equipment for guidance.
• Ensure training, comfort and fit testing are provided before use. Respirators should not be shared.
• Maintain and store respiratory protective equipment properly.

Dust control technologies and techniques

• Access resources about dust mitigation techniques and technologies for Queensland mines.

Figure 2

See the OSH Answers document Substitution of Chemicals: Considerations for Selection for more information.

What are examples of engineering controls methods?

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Engineering controls are methods that will remove the hazard at the source, before it comes in contact with the worker. 

Engineering controls can be built into the design of a plant, equipment, or process to minimize the hazard. Engineering controls are a very reliable way to control worker exposures as long as the controls are designed, used, and maintained properly. Examples of engineering controls are:

• Isolation &#; separating workers from the hazard by distance or the use of barriers
• Enclosures &#; placing the material or process in a closed system (e.g., enclosed machines, booths, etc.)
• Guarding and shielding &#; using guards around moving parts of machinery
• Ventilation &#; using local exhaust or general dilution ventilation to remove or reduce airborne products
• Mechanical lifting devices&#; using mechanical methods to lift or move objects instead of manual lifting
• Guardrails &#; using guardrails to prevent a fall

More information on engineering controls include the following:

Process Control

Process control involves changing the way a job activity or process is done to reduce the risk. Monitoring should be done before and as well as after the change is implemented to make sure the changes did, in fact, control the hazard.

Examples of process changes include to:

• Use wet methods rather than dry when drilling or grinding. "Wet method" means that water is sprayed over a dusty surface to keep dust levels down or material is mixed with water to prevent dust from being created.
• Use steam cleaning instead of solvent degreasing (but be sure to evaluate the potential high temperature hazard being introduced such as heat stress).
• Float "balls" on open-surface tanks that contain solvents (e.g., degreasing operations) to reduce solvent surface area and to lower solvent loss.
• Instead of conventional spray painting, try to dip, paint with a brush, or use "airless" spray paint methods. These methods will reduce the amount of paint that is released into the air.
• Decrease the temperature of a process so that less vapour is released.
• Use automation - the less workers have to handle or use the materials, the less potential there is for exposure.
• Use mechanical transportation rather than manual methods.

Enclosure and Isolation

These methods aim to keep the chemical "in" and the worker "out" (or vice versa).

An enclosure keeps a selected hazard "physically" away from the worker. Enclosed equipment, for example, is tightly sealed and it is typically only opened for cleaning or maintenance. Other examples include "glove boxes" (where a chemical is in a ventilated and enclosed space and the employee works with the material by using gloves that are built in), abrasive blasting cabinets, or remote control devices. Care must be taken when the enclosure is opened for maintenance as exposure could occur if adequate precautions are not taken. The enclosure itself must be well maintained to prevent leaks.

Isolation places the hazardous process "geographically" away from the majority of the workers. Common isolation techniques are to create a contaminant-free or noise-free booth either around the equipment or around the employee workstations.

Ventilation

Ventilation is a method of control that  "adds" and "removes" air in the work environment. General or dilution ventilation can remove or dilute an air contaminant if designed properly. Local exhaust ventilation is designed to remove the contaminant at the source so it cannot disperse into the work space and it generally uses lower exhaust rates than general ventilation (general ventilation usually exchanges air in the entire room).

Local exhaust ventilation is an effective means of controlling hazardous exposures but should be used when other methods (such as elimination or substitution) are not possible.

Figure 3 Example of Local Exhaust Ventilation

The design of a ventilation system is very important and must match the particular process and product in use. Expert guidance should be sought. It is a very effective control measure but only if it is designed, tested, and maintained properly.

Because products are exhausted to the outdoors, you should also check with your local environment ministry or municipality for any environmental air regulations or bylaws that may apply in your area.

What are examples of administrative controls?

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Administrative controls involve developing procedures to ensure the work is conducted in a way that minimizes the hazard. Examples include developing or changing policies, implementing or improving training and education, and developing or enhancing work practices and procedures.

Administrative controls are ranked lower than elimination, substitution, and engineering controls because this method does not necessarily remove or reduce the hazard from the workplace. For example, administrative controls limit workers' exposures by scheduling shorter work times in contaminant areas or by implementing other "rules". These control measures have many limitations because the hazard itself is not actually removed or reduced. Administrative controls should be used in combination with other control measures where possible. 

Methods of administrative control include:

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• Using job-rotation schedules or a work-rest schedule that limit the amount of time an individual worker is exposed to a substance.
• Implementing a preventative maintenance program to keep equipment in proper working order
• Scheduling maintenance and other high exposure operations for times when few workers are present (such as evenings, weekends).
• Restricting access to a work area.
• Restricting the task to only those competent or qualified to perform the work.
• Using signs to warn workers of a hazard.

More information about types of administrative controls is provided below:

Work Practices

Elements of safe work practices include:

• Developing and implementing safe work procedures or standard operating procedures.
• Training and education of employees about the operating procedures as well as other necessary workplace training (including WHMIS).
• Establishing and maintaining good housekeeping programs.
• Keeping equipment well maintained.
• Preparing and training for emergency response for incidents such as spills, fire, or employee injury.

Education and Training

Employee education and training on how to conduct their work safely is a critical element of any complete workplace health and safety program. Training must cover not only how to do the job safely but it must also ensure that workers understand the hazards and risks of their job, and the controls in place to protect them. It must also provide them with information on how to protect themselves and co-workers.

Good Housekeeping

Good housekeeping is essential to prevent the accumulation of hazardous or toxic materials (e.g., build-up of dust or contaminant on ledges, or beams), or hazardous conditions (e.g., poor stockpiling).

For more information about workplace housekeeping, please see the OSH Answers document Workplace Housekeeping - Basic Guide.

For more information about combustible dust, please see the OSH Answers document Combustible Dusts.

Figure 4

Emergency Preparedness

Being prepared for emergencies means making sure that the necessary equipment and supplies are readily available and that employees know what to do when something unplanned happens such as a release, spill, fire, or injury. These procedures should be written and employees should have the opportunity to practice their emergency response skills regularly.

Please see the OSH Answers document on emergency planning for more information.

Personal Hygiene Practices and Facilities

Personal hygiene practices are another effective way to reduce the amount of a hazardous material absorbed, ingested, or inhaled by a worker.

Examples of personal hygiene practices include:

• Washing hands after handling material and before eating, drinking or smoking.
• Avoiding touching lips, nose, and eyes with contaminated hands.
• No smoking, drinking, chewing gum or eating in the work areas - these activities should be permitted only in a "clean" area.
• Not storing hazardous products in the same refrigerator as food items.

Please see the OSH Answers documents on Workplace Housekeeping,  Hand Washing: Reducing the Risk of Common Infections and Good Hygiene Practices - Reducing the Spread of Infections and Viruses for more information.

What should I know about personal protective equipment (PPE) as a hazard control method?

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Personal protective equipment (PPE) refers to anything workers wear to help protect them from a workplace hazard. 

The use of PPE as the main method to control exposures should be limited to situations where elimination, substitution, engineering, or administrative controls are not practicable, or when:

• Additional protection is required because other control methods are not sufficient to reduce the hazard
• The hazard is a result of a temporary or emergency condition

PPE limits exposure to the harmful effects of a hazard but only if the PPE is worn and used correctly.  Examples of PPE include:

• Respiratory protection
• Skin protection (e.g., coveralls, aprons, full body suits)
• Gloves
• Eye protection (e.g., face shield, goggles)
• Foot protection
• Hearing protective devices (e.g., ear plugs, ear muffs)

The choice of what type of PPE is required must be based on the specific hazard found at the workplace.

No matter which type of PPE is used, it is essential to have a complete PPE program in place. For more information about PPE programs, please see the following document Designing an Effective PPE Program.

Can more than one control method be used or followed?

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Yes.  Sometimes a hazard cannot be controlled using a single type of control method.  If a hazard cannot be eliminated, a combination of controls may be required. 

For example:

• Using a scissor lift instead of a ladder (substitution).  Workers should be trained on the safe use of the equipment and follow safe work procedures (administrative controls).  When working at heights, workers should also use PPE, including a full body harness and lanyard attached to an anchor point, there is a risk of injury from falling. 
• Driving in the winter for work.  Controls may include not driving during extreme winter weather (elimination), determining if there are any other options to driving such as public transit (substation), use of winter tires (engineering), and driver training (administrative).

Should the adequacy of controls be reviewed or evaluated?

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Yes.  It is important to determine the effectiveness of the control methods implemented and adjust as required.

Controls must not create new hazards. For example, if wearing PPE contributes to other hazards (e.g., heat stress), then it is important to review if other controls methods are possible or if additional precautions are needed. 

Monitor both the hazard and the control method to make sure that the control is working effectively and that exposure to the hazard is reduced or eliminated. Consider the following questions:

• Have the controls effectively eliminated or reduced worker exposure?
• Have any new hazards been created?
• Are new hazards appropriately controlled?
• Are any other methods required?
• Are workers trained on the control methods?
• What else can be done to eliminate or reduce exposure?
• If there is a change at the workplace, does this impact the hazard or the control methods?

 

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