OSH Principles & Risk Assessment



- Definition

- Aim

- Level of Risk

- Factors


- Definition

- Science of Occupational Safety

- Science of Occupational Health

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Mr. Tony Tung

Risk Assessment


A risk is the likelihood of a hazard actually causing harm.

A hazard is something with the potential to cause harm. Some examples are trip hazards in corridor, glare from VDU's, moving heavy objects and using chemicals.

An assessment is an investigation of the use or potential use of a hazardous substance/equipment/operation in the workplace to understand and minimize the risks to the health or safety of workers using and/or carrying out that substance/equipment/operation.



Risks associated with a hazard need to be assessed to determine how severe (or dangerous) they are. Assessing the risks allows decisions to be made as to what hazards or risks need to be controlled and to set priorities for introducing controls.


Level of Risk


Training, material safety data sheets (MSDS), statistics and codes of pracetice (CoP) can help with estimating the consequence and likelihood of an injury occurring in a group of employees.



To determine the level of risk, all of the following need to be considered:

Severity :
This factor concerns the extent of the injury or degree of harm caused if exposed to the hazard (e.g.,. fatality, major injury, minor injury, no injury).

Probability :
What is the likelihood of harm occurring if a person is exposed to the hazard? This could range from inevitable through to unlikely.

Exposure :
The significance of the risk of injury on illness/harm may be affected by the level of exposure to a hazard. Exposures would take into account how often employees are exposed to a hazardous situation (frequency) and the length of time of this exposure (duration).

Human Differences :
Hazards need to be assessed in terms of the individuals who are exposed:

- their skills

- experience

- training

- physical capabilities


Principles of Occupational Health & Safety

The term OCCUPATIONAL SAFETY encompasses those environmental hazards that :

- exist in the short term only

- occur randomly over time

- are potentially disabling at exposure

Some examples of occupational safety hazards are a fire, a fall, a gross chemical spill, a machine accident.

The term OCCUPATIONAL HEALTH encompasses those environmental hazards that :

- are continuously present

- or occur at known times

- are potentially disabling over time

Some example of occupational health hazards are airbone chemicals, radiation, biohazards, occupational strain.


Science of Occupational Safety

1. Coincidence of People and Energy

Occupational safety is related to the (absence of) coincidence between a person and some form of excessive energy.

2. The appropriate focus for safety practice is the anticipation (and control) of the random error.

If the error can be eliminated, then the accident it may produce will be eliminated, and the injury that may result from the accident cannot then occur.

Injury Causation Model 


3. Control strategies for a Safe Working Environment

Given, (a) the definition of the jurisdiction of occupational safety,

            (b) the Injury Causation model,

then, the logical framework for injury prevention is

- Anticipate the random error/energy coincidence

- Control to reduce the frequency/severity of such coincidence

- Prior resource allocation to minimize the loss caused by such coincidence


Science of Occupational Health

1. Environmental Factors and their Effect on People

Three levels of effect can be investigated, depending on the extent and significance of the deviation from homeostasis caused by the environmental factor.

These three levels, in order of increasing extent and biological significance, are

- influence on comfort

- influence on work performance

- influence on health

2. Steps in controlling occupational health environmental hazards :

(i)   Recognize the toxic/traumatic factors

(ii)  Evaluate the dose to the worker

(iii) Control to reduce or optimize dose

3. Hazardous Environmental Factors wpe3.jpg (5756 bytes)

CHEMICAL Solids, dusts, fumes
Liquids, sprays, mists
Gases, vapours
Mutagens, carcinogens, teratogens
* Nutrients
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PHYSICAL * Noise, vibration
* Thermal : heat, cold
  Electromagnetic radiation:
      * non-ionizing
      * visible
* Pressure
MECHANICAL * Ergonomics :
      work physiology
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PSYCHOSOCIAL * Work organization
* Stress

* factors needs to be optimized, rather than eliminated


4. System for Dose Limitation


No practice adopted unless it produces a positive net benefit i.e. benefits outweigh the losses.


All doses to exposed individuals are made as low as reasonably achievable, social and economic factors being taken into account.


For hazards that produce a toxic effect, a dose limit or an exposure standard be set that is NOT to be exceeded.


5. Occupational Hygiene Model

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6. Hierarchy of Controls

This principle follows these steps :

(1) Elimination - the ideal way to control risks.

(2) Substitution - substitute with something of a lesser risk.

(3) Engineering - engineering controls take many forms. The best is one which removes the hazard at its source. This might be done by :

* Automating the operation
* Isolation the operation
* Isolating the worker
* Local exhaust ventilation

(4) Administrative procedures - some examples are :

* Rotation of workers to reduce the period of exposure
* Reducting the number of worker exposed.
* Good housekeeping
* Personal hygiene

(5) Personal protective equipment (ppe) - where it is not possible to use any of the above methods, providing workers with ppe may be the only choice. Make sure that ppe is always :

            (i) Properly selected.

           (ii) Fitted correctly.

          (iii) Well maintained, clean and routinely inspected.

(6) Combination - in most cases, a combination of control methods are necessary to satisfactorily control hazards in the workplace.


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