Hierarchy of control measuresAs illustrated in the previous example there are many ways of reducing the risk of negative health effects at the workplace. The control measures to reduce risks can be categorized in terms of administrative and engineering controls, and/or in terms of control location, i.e. source, path and receiver (Figure below). Control measures to reduce exposures could be established at the source, the path and/or at the receiver/worker. ©University of Bergen Examples of different ways to group a set of control measures. ©University of BergenThe best way to achieve control is by addressing the source of the hazard/contamination, and consequently this is placed on top of the control measure hierarchy. Substitution of currently-used materials with less hazardous materials is one of the most effective ways for eliminating or reducing exposure to materials that are toxic or pose other hazards.If control by source cannot be achieved or does not resolve the problem then an attempt should be made to control the risk by interrupting the path of exposure between the hazardous material and the worker/receiver. In terms of “path”, engineering controls are preferrable to administrative/procedural controls: This is not necessarily due to a question of effectiveness but more to the potential longevity of the measure. While an engineering control requires a physical change to the workplace, administrative controls require the workers or employers to do something.Personal protective equipment is considered to be the least effective measure and is placed at the bottom of the control hierarchy. Personal Protective Equipment (PPE) requires the workers to wear something and should be the last resort for reducing exposures. It is only if none of the measures in the upper part of the control hierarchy can be achieved, should one resort to a situation where the primary control measures are based around the workers themselves.
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Occupational Health in Developing Countries
Measures that can be applied at the source of the contamination include:
- Eliminate the source, – examples;
o use electric instead of diesel powered forklift trucks
o use automatic instead of manual machines for hazardous work such as cutting and skinning
- Substitution – using a less hazardous chemical or process;
o asbestos has been banned in many countries, and is substituted by synthetic mineral fibers for insulation
o lead in paint has been substituted by e.g. zink and titanium dioxides
- Isolation / containment / enclosure;
o enclose sources or the employee, or the source and some employees together rather than all employees
o place the source in a separate location from the employees
- Modification of the source or process
o replace dry sweeping with broom with vacuum cleaning or wet methods
o use pellets instead of powders
o use pre-mixed or diluted chemicals instead of manually mixing or diluting chemicals at the workplace
- Automation – use robotics, remote or computer aided products
- Local exhaust ventilation – using ventilation to capture the contaminant at the source, to prevent it dispersing
Control along the pathWhen the contaminant is dispersing, it is more difficult and fewer options are available. They include;
- General ventilation – which dilutes the contaminant concentration
- Increasing the distance between the source and the workers (i.e.: increasing the length of the pathway so that there is more dispersion and dilution)
- Use of screens and partial barriers
Worker based (receiver) controls include:
- Administrative controls – rotating workers, limiting the length of time they work in a location
- Personal protective equipment (PPE) – wearing something that decreases or limits the effects of the contaminant (Note: the contaminant has already reached the worker).
Personal protective equipmentDifferent types of personal protective equipment (PPE) are illustrated below. Head protection. ©ColourboxEye & Face protection. ©ColourboxHearing protection. ©Colourbox Respiratory protection. ©Colourbox Hands / Gloves protection. ©ColourboxBody / Clothing protection. ©Colourbox Foot protection. ©ColourboxProtection against falling. ©Colourbox
Personal protective equipment – chemical exposureThe personal protective equipment required depends on the type of chemical compound used in any given process, and the protection necessary to reduce exposure to acceptable levels. For instance, when selecting gloves one has to take into account that different glove materials provide different levels of resistance to the effects of hazardous chemicals. This is related to the ability of the chemical to penetrate, degrade and/or penetrate through the glove material. A range of different glove materials exists, such as latex, nitrile, PVC and neoprene. Glove charts are available from the manufacturers to assist in selecting type of gloves to use when working with chemicals. However, expert knowledge is needed to make the appropriate choice for particular task and chemicals.Similarly, there is a broad range of different types of personal respiratory protective devices (respirators). There are two main types of Air Purifying Respirators. These are effective against either:
- contaminants in particulate form or
- contaminants in gaseous or vapour form
Using a Combination of Controls or “The Swiss Cheese Model”In many cases, it will be necessary to use a combination of measures to appropriately manage risk exposure. For example, a toxic chemical could be replaced with a less hazardous one (substitution), safe work procedures (administrative measures) can be introduced, and personal protective equipment can be provided for workers to use. This concept is commonly presented as a material moving through layers of cheese containing holes (Swiss Cheese) as illustrated in the figure below.
“The Swiss Cheese Model” illustrates that it is usually necessary to use a combination of measures to appropriately manage to reduce exposure to a hazard.© University of Bergen/Arjun Ahluwalia
Occupational Health in Developing Countries
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