The Hierarchy Of Control For Chemical Safety

The Hierarchy Of Control For Chemical Safety

Hierarchy Of Control For Chemical Safety

There are a number of ways to control the risks associated with hazardous chemicals. Some control measures are more effective than others. Control measures can be ranked from the highest level of protection and reliability to the lowest. This ranking is known as the hierarchy of control.

You must always aim to eliminate a hazard and associated risk first. If this is not reasonably practicable, the risk must be minimised by using one or more of the following approaches:

  • Substitution
  • Isolation
  • Implementing engineering controls.

If a risk then remains, it must be minimised by implementing administrative controls, so far as is reasonably practicable. Any remaining risk must be minimised with suitable personal protective equipment (PPE).

Administrative control measures and PPE rely on human behaviour and supervision and when used on their own, tend to be the least effective ways of minimising risks


This means removing the hazard or hazardous work practice from the workplace. This is the most effective control measure and must always be considered before other control measures. For example, not using a hazardous chemical or eliminating exposure by:

  • using nails instead of using chemical based adhesives
  • eliminating a handling activity and potential worker exposure by purchasing pre-mixed or diluted chemicals instead of manually mixing or diluting chemicals at the workplace.

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Substitution is the replacement of a hazardous chemical with a chemical that is less hazardous and presents lower risks, for example:

  • substituting a less volatile material to control a vapour hazard may cost less than the installation and maintenance of a mechanical ventilation system
  • substituting a highly flammable liquid with one that is less flammable or combustible
  • using hazardous chemicals with a single hazard class rather than those with multiple hazards
  • substituting high hazard chemicals like carcinogens, mutagen, reproductive toxicants and sensitisers, with less hazardous chemicals
  • using diluted acids and alkalis rather than concentrates
  • using a product in either paste or pellet form rather than as dust or powder.


Isolation involves separating people from the chemicals or hazards by distance or barriers to prevent or minimise exposure. Examples of isolation include:

  • Isolate workers from chemicals use of closed systems such as those used during the processing and transfer of flammable liquids in petroleum refineries, or the use of glove boxes or glove bags
  • placing a process, or a part of it, within an enclosure which may also be fitted with exhaust extraction to remove contaminants

Isolating operations in one room with access restricted to properly protected personnel

Placing operators in a positive pressure cabin that prevents airborne contaminants entering

Distancing workers from hazardous chemicals and any potential hazards generated by their use.

  • Isolate chemicals from other chemicals Hazardous chemicals should be physically separated from any chemicals or other things that may be incompatible. This is achieved by distance, barriers, or a combination of both barriers and distance. Isolation as a control measure is usually used to control physicochemical risks (for hazardous chemicals that are dangerous goods) because of the greater consequences when incompatible materials interact. However, it is also important to consider isolation for other hazardous chemicals. The choice of isolation measure used will depend on a range of factors, including the quantity of hazardous chemicals stored and handled in the work area
  • the types of installation involved and the processes applied to the hazardous chemicals in the work area and their associated hazards
  • all other activities in the work area which may increase the risks
  • any other control measures in place that will minimise the risks.

If possible, separation distances should be applied in a way that would not require additional control measures. If this is not possible, barriers may be required.

When choosing to use a barrier, you should consider:

  • the effect that climatic elements may have a barrier and its effectiveness
  • the level of fire resistance provided by the barrier
  • the structural capability which may be required to withstand weather, and overpressure resulting from internal or external incidents.

When storing chemicals on shelving or other storage systems, hazardous chemicals should not be stored above or below other chemicals or other things which may be incompatible, potentially interact or contaminate. Hazardous chemicals should never be stored where they could contaminate food, food packaging and other items like personal use products, cosmetics, cigarettes, medication and toiletries.

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Engineering controls are physical in nature, including mechanical devices or processes that eliminate or minimise the generation of chemicals, suppress or contain chemicals, or limit the area of contamination in the event of spills and leaks. They often involve partial enclosure, use of exhaust ventilation or automation of processes. Examples of engineering controls include:

  • using intrinsically safe electrical equipment in hazardous areas
  • using robots to minimise operator exposure, for example, spraying in coating operations
  • partially enclosed and ventilated spray booths or fume cupboards
  • fully enclosed ventilation booth (see diagram 1)
  • local exhaust ventilation to capture airborne contaminants close to their point of release.

Local exhaust ventilation is designed to capture airborne contaminants close to the source of generation. This prevents them contaminating the working environment. The ventilation should be arranged to prevent contaminants from entering the breathing zone of the operator. The exhaust extraction shown in diagram 4 is a well-designed system, while that shown in diagram 5 is poorly designed as it carries contaminants directly through a person’s breathing zone.

Design considerations for ventilation systems

Ventilation is a means of maintaining a safe atmosphere by the introduction or recirculation of air; by natural, forced or mechanical means. Maintaining a safe atmosphere in the storage and handling area of hazardous chemicals is an important control measure. Recirculation should be avoided unless precautions are taken to detect and avoid harmful contamination and prevent accumulation of airborne contaminants. Recirculation should only be used where temperature control is required.

A ventilation system should operate exclusively for the particular building, room or space. Where this is not practicable, the system may be linked to another area provided that this does not increase the risk to exposure of hazardous chemicals, for example by recirculating hazardous or flammable vapours or spreading them into other areas where that chemical is not being used.

Ventilation systems should be suitable for the types of hazardous chemicals on the premises. For example, if a hazardous chemical has vapours which are denser than air, these will accumulate in low lying areas. In this case, extraction of vapours should be from the lowest point and fresh air introduced from above.

Exhaust systems and ducting should be resistant to the vapours, mists or dust being extracted. The risk of fire propagation can be reduced by installing self-closing fire dampers, for example in laboratory fume cupboards. Extraction ducting should not be linked to multiple items of plant if there is any risk of fire spreading through the ducting. Provision against flashback, for example by installing flame arresters, may be necessary.

Exhaust gases and air should be discharged where it will not cause other hazards. For example, fume cupboard extraction systems should not exhaust close to air intakes and should be in compliance with any local building or environment protection requirements. Exhaust systems can also be fitted with means to reduce airborne contaminants which may be harmful to the environment or people prior to discharge to the atmosphere. This might include particulate filters, absorbents and adsorbents (e.g. carbon), catalysts, scrubbers or burners.

Regular checks of these systems should be included in planned maintenance schedules to ensure that vents remain unobstructed.

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Mechanical ventilation

Inlet and outlet vents located on opposite sides of the storage area at low levels provide airflow across the floor. Where both inlet and exhaust are mechanically assisted, capacities and rates should be adjusted to ensure that the pressure inside the store or room never exceeds that outside and airflow into any adjoining work areas and offices is prevented.

Local Exhaust Ventilation

Local exhaust ventilation is used to remove airborne contaminants before they reach the breathing zone of workers in the area. It is used for effective control of more highly toxic contaminants created in large quantities and is applied close to the source of generation. It is more effective than increasing general ventilation to try to dilute toxic contaminants.

Natural Ventilation

Natural ventilation can be used to control small amounts of relatively low toxicity contaminants including dust, fumes, gases and vapours which have low and steady rates of generation. It requires a large building space for dilution and relatively large air flow through open doors, windows or ceiling exits. For solvent storage areas, where heavier than air vapours may accumulate in lower regions (e.g. near floor level) with a subsequent build-up of hazardous concentrations, vents should be provided at a level immediately above any spill containment, on the opposite sides of a room or space, to provide for airflow across the storage or handling area. High level ventilation may be necessary for temperature control (e.g. roof vents to allow the escape of warm air).

Note: Vents in a screen wall may negate any fire protection or vapour barriers.

To ensure the effectiveness of ventilation systems, these should be designed in accordance with appropriate technical standards, and installed and maintained by qualified or experienced persons, such as engineers or occupational hygienists.

Further information on the design of ventilation systems can be found in:

  • AS 1940: The storage and handling of flammable and combustible liquids
  • AS/NZS 60079.10.1: Explosive atmospheres – Classification of areas – Explosive gas atmospheres [IEC 60079-10-1, Ed 1.0 MOD]
  • HSG258 Controlling airborne contaminants at work: A guide to local exhaust ventilation (LEV); 2nd Edition 2011; Health Safety Executive (Great Britain)
  • ACGIH Industrial Ventilation: A Manual of Recommended Practice, 25th Edition; American Conference of Governmental Industrial Hygienists.

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Administrative controls should only be considered when other higher order control measures are not practicable, or to supplement other control measures. For carcinogens, administrative controls should only be used to provide additional protection.

Administrative controls are also relevant for emergencies when other control measures fail, such as for managing spills and leaks and are particularly important for those workers who are required to clean up spills, or who carry out regular cleaning and maintenance work. Examples of administrative controls include:

  • written policies and work procedures (for example safe work method statements)
  • reducing the number of workers exposed to the chemical (for example by performing the task out of normal work hours or by restricting worker access to certain areas)
  • reducing the duration and/or frequency of workers’ exposure through specific work procedures (for example, job rotation)
  • reducing quantities of hazardous chemicals through inventory reduction – this may include just in time ordering rather than storing large quantities of hazardous chemicals and prompt disposal of hazardous chemicals that are no longer required
  • implementing procedures where only staff who are involved in the use, handling, storage or generation of hazardous chemicals are allowed access to high risk areas where there may be a greater risk of exposure
  • implementing procedures to prevent introduction of ignition sources into hazardous areas
  • reducing the period of time in which a chemical could escape into the work area (for example, by minimising the time that mixers, reactors or ovens are open to the environment both during and after use)
  • safe work practices, including good housekeeping, including regular cleaning of work areas
  • changing packaging material to minimise exposure during handling (for example purchasing liquids in ready to use packages instead of decanting from large containers)
  • using vacuuming or wet methods to suppress dust that may be generated during dry sweeping
  • keeping containers of hazardous chemicals tightly closed when not in use
  • cleaning up spills immediately
  • prompt cleaning of residues from empty containers that have held hazardous chemicals
  • prohibiting eating, drinking and smoking in potentially contaminated areas
  • providing washing facilities for rinsing off chemicals (e.g. hand washing, safety showers, laundering of clothes).
  • Training and supervision should always be provided to ensure administrative controls are effectively implemented.

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If personal protective equipment (PPE) is to be used at the workplace, the person conducting the business or undertaking must ensure that the equipment is:

  • selected to minimise risk to health and safety
  • suitable for the nature of the work and any hazard associated with the work
  • a suitable size and fit and reasonably comfortable for the person wearing it
  • maintained, repaired or replaced so it continues to minimise the risk
  • used or worn by the worker, so far as is reasonably practicable.

A worker must, so far as reasonably able, wear the PPE in accordance with any information, training or reasonable instruction.

PPE includes overalls, aprons, footwear, gloves, chemical resistant glasses, face shields and respirators.In most circumstances, PPE should not be relied on to control risk. It should be used only as a last resort when all other reasonably practicable control measures have been used and the risk has not been eliminated, or as interim protection, until higher level, controls are implemented. There may also be situations when the use of other controls is not practicable.

For some high-risk activities, such as spray painting, abrasive blasting and some emergency response actions, PPE should always be used to supplement higher level control measures.

The effectiveness of PPE relies heavily on workers following instructions and procedures correctly. If PPE must be used for long periods, if dexterity and clear vision are needed for the task, or if workers have not been adequately trained on how to fit and use PPE properly, workers might avoid using it.

The best way to determine this is to observe workers performing the task. If they discard the PPE or do not use it, this may indicate that it does not fit, is uncomfortable or is a hindrance in the work. You should also observe workers after the task is complete to ensure that the PPE they have used is stored and maintained correctly.

PPE must be suitable for the task being performed. Examples include:

  • Choosing appropriate chemical-resistant gloves offering the best resistance to the chemical being used. Some gloves may be resistant to some solvents but not others.
  • Using full-face, air-fed respirator rather than a half-face respirator during spray-painting operations to reduce exposure to hazardous chemicals like isocyanates, which can cause skin and respiratory allergic reactions.




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