Crystalline silica is a natural mineral found in construction materials such as concrete, bricks, tiles, hebel, mortar and engineered stone. When these materials are ground, cut, drilled, sanded, loaded or demolished, or when dust is swept or cement powder is mixed and/or shovelled, respirable crystalline silica (RCS) is released into the air. RCS is so fine that the particles are 100 times smaller than a grain of sand and not visible. Therefore, workers breathe in this dust without knowing it.
Exposure standards and risks
The exposure standard for crystalline silica is 0.05mg/m3 as a time-weighted average (TWA) airborne concentration over 8 hours.
Duty holders are required to ensure worker exposure does not exceed this standard.
SafeWork SA recommends that workers exposure should be below half the exposure standard (0.025mg/m3) as exposure above this level poses significant risk to construction and demolition workers health.
Exposure to RCS is caused by one, or a combination of, factors including:
- high-energy tools like cut-off saws, grinders and jack hammers producing a lot of RCS in a very short time, both indoors and outdoors
- working in an enclosed workspace
- leaks or spillages in ventilation causing recirculation of RCS dust
- insufficient water placement or inadequate supply to suppress dust
- inappropriate clean-up of dust containing RCS, for example, dry sweeping rather than wet cleaning
- contamination of clothing and surfaces with dust containing RCS
- using compressed air for removing RCS dust from clothing
- accumulated dust containing RCS being ‘kicked-up’ from the ground or other surfaces by moving vehicles and people
- RCS dust remaining in the air for long periods due to inadequate ventilation
- the duration and frequency of the task
- inadequate supervision, resulting in controls not being maintained
- the controls listed in the Safe Work Method Statement are not being followed
- principal contractors not having adequate arrangements in place for ensuring compliance.
If it is not certain whether the concentration of an airborne contaminant exceeds the relevant exposure standard, a person conducting a business or undertaking must ensure air monitoring is carried out on the workplace.
For further information see: Using RPE to minimise risk of exposure.
RCS can be harmful when inhaled over a long period of time at low to moderate levels, or short periods at high levels. Crystalline silica has been classified as a carcinogen.
Breathing in RCS can lead to serious diseases, including:
- silicosis - irreversible stiffening of the lungs
- lung cancer
- chronic obstructive pulmonary disease
- kidney disease.
Construction and demolition workers can be at risk of developing these diseases.
Workers exposed to RCS must be provided with health monitoring.
Controlling exposure risks
PCBUs must consult with their workers and any health and safety representatives, when identifying hazards and risks associated with crystalline silica exposure, and when deciding on how to control risks.
To control the risk associated with exposure to RCS, PCBUs must apply the hierarchy of control. A PCBU must, so far as is reasonably practicable, eliminate the risk of exposure in their workplace, for example, by using:
- non crystalline silica-containing products
- different method of work, for example, a direct fastening system
- pre-manufactured products that do not need to be cut, ground or polished.
If it is not reasonably practicable to eliminate a risk associated with RCS, the PCBU must reduce the risk so far as is reasonably practicable by:
- use products that have less silica in them
- less powerful tools, for example, a block splitter instead of a cut-off saw
- physical barriers and exclusion zones between different work groups
- fully enclosed operator cabins with properly designed and maintained high efficiency air filtration
- silica work processes conducted outdoors away from other workers where possible
- engineering controls, or
- a combination of any of the above risk control measures.
If the risk of exposure still remains, these controls must be added:
- administrative controls
- good housekeeping
- rotating workers
- signage, to alert others
- procedures and safe work methos statements
- personal protective equipment
- respiratory protective equipment (RPE)
- disposable coveralls.
You may need more than one control measure to control the risk sufficiently.
If workers regularly dry cut, grind, crush, drill, sweep or demolish material containing crystalline silica without engineering controls in place, it is highly likely that the exposure standard will be exceeded.
SafeWork SA believes it is reasonably practicable to have engineering controls in place in all but very rare situations.
There are two main dust controls used in construction and demolition:
- on-tool dust extraction
- This method removes dust as it is being produced and prevents it from being released into the atmosphere. It is a type of local exhaust ventilation system that fits directly onto the tool. This system consists of several individual parts – the tool, capturing hood, an M or H class vacuum or dust extraction unit.
- water suppression
- Water or fine mist suppression can also be used to control silica dust when local exhaust ventilation is not suitable. However, it needs to be used correctly. This means enough water supplied at the right levels for the whole time that the work is being done. Spray bottles and wetting the material beforehand does not work.
Engineering controls require maintenance, and workers need to understand how to properly use them for these controls to remain effective.
For effective selection and use of engineering controls, manufacturer’s instructions may include information on:
- water flow rates
- vacuum equipment air flow rate and capacity
- rotation of the blade (speed, direction)
- maintenance and changing of blades, and
- frequency of changing water.
Where it is not possible to use engineering controls, tasks that involve exposure to crystalline silica may be performed with a tight-fitting respirator for a very short period of time over the day. For example, overhead drilling for a total of 15 minutes or less, assuming there is no further exposure to the worker for the remainder of the day (Occupational Safety and Health Administration USA, 2017).
Construction workers may be exposed to higher levels of exposure to RCS when engineered stone benchtops are being cut on the construction site.
Respiratory protective equipment (RPE)
When engineering controls do not adequately control risks of exposure to silica dust, PCBUs must provide their workers with RPE.
Wearing a respirator does not stop silica from becoming airborne. Respirators should not be used as the primary means of control, but rather in combination with higher order controls like local exhaust ventilation or water suppression.
It is important to choose the right respirator for the job and workers must wear it for the whole time silica is in the air. If workers wear a tight-fitting respirator, they must pass a respirator fit-test to ensure it provides a good seal for their face size and shape. Workers must be completely clean-shaven or clean-shaven beneath the seal of the respirator for the respirator to seal properly.
For more information see: Respiratory protective equipment.
Information, instruction and training
A PCBU must provide their workers with any necessary information, instruction, training and supervision to enable them to do their work safely.
Training should cover at a minimum:
- crystalline silica hazards and health risks
- how to effectively use controls
- how to maintain and clean equipment, including personal decontamination
- use and maintenance of RPE
- how to dispose of waste
- what to do if controls fail.
The structure, content and delivery of the training needs to take into account any special requirements of the workers being trained. For example, information, instruction and training may need to be provided in a language other than English. Refresher training should be provided regularly.
Safe Work Method Statements
The Work Health and Safety Regulations 2012 (SA) lists aspects of construction work considered high risk, and for which a safe work method statement (SWMS) is required.
High risk construction work includes work ‘carried out in an area that may have a contaminated or flammable atmosphere’.
Task involving silica-containing materials may be considered high risk construction work if RCS contaminates the work atmosphere.
A SWMS helps a PCBU to inform workers at the construction site of any health and safety risks and how they will be managed.
At a construction project,:
- the contractor must give a copy of the SWMS to the Principal Contractor, and
- the Principal Contractor must take reasonable steps to obtain a copy of the SWMS.
For further information see: SWMS for high risk construction work.
Worker exposure levels at a construction project are based on total RCS exposures from all sources and must take into account all conditions that may add or contribute to the worker’s overall exposure level.
At a construction project, it is foreseeable that worker exposure may be affected by activities undertaken by other contractors. On many construction projects, there can be multiple contractors performing RCS generating tasks. The RCS generated by these tasks can impact other contractors. Such impacts/exposures are called secondary exposures.
Principal contractors and PCBUs need to consider these secondary exposures when determining whether worker exposure will remain below the TWA under any foreseeable conditions, including the potential failure of a control measure.
If, however, the principal contractor can ensure, either due to the nature and timing of the work, or through work practice controls, that workers will not be exposed to RCS generated by other contractors, then the PCBU undertaking the task would not need to consider secondary exposures in determining whether its own workers are at risk of exceeding the TWA.
A Principal Contractor at a construction project must have in place arrangements for ensuring compliance with:
- managing risks from airborne contaminants, and
- personal protective equipment.
A Principal Contractor’s written WHS management plan must also have the arrangements for the collection and any assessment, monitoring and review of safe work method statements at the workplace.
A Principal Contractor’s arrangements could include:
- obtaining a copy of the air monitoring results from contractors who specialise in working with crystalline silica products.
- having an engineering control for all RCS generating tasks
- keeping maintenance records of engineering controls
- having the correct M or H class dust extraction unit
- having permit to work systems, prior to the contractor processing silica products
- keeping records of fit-testing for workers wearing tight fitting respirators
- having a dedicated area for RCS generating tasks, such as cutting
- regularly monitoring RCS generating tasks to ensure compliance with the SWMS
- including in the contractors SWMS information on:
- control measures
- respirator use
- control measure failures
- consideration of other contractors in the immediate area
For further information see: Principal contractors and construction projects.