Hazard and Risk 

Hazard

A hazard is "an inherent physical or chemical characteristic that has the potential for causing harm to people, property, or the environment”.

In chemical processes: “It is the combination of a hazardous material, an operating environment, and certain unplanned events that could result in an accident”.

Hazard is the potential for harm.

A hazard is often associated with a condition or activity that can cause undesired consequences such as injury or illness if left uncontrolled.

Basically, a hazard can cause harm or adverse health effects to individuals or to organizations as property or equipment losses.

Types of hazard

• Chemical hazards
• Physical hazards
• Biological hazards (biohazards)
• Ergonomic hazards
• Noise hazards

Chemical hazards

Chemicals can affect skin by contact. Chemicals can also enter our body either through the inhalation or digestive system if air is contaminated with chemicals, vapor, mist or dust. The accumulation of chemicals in or on our body will cause acute (immediate) effect or chronic (long-term) effect.

Physical hazards

Physical hazard will cause injury risks on our body. This category includes the hazards from working in confined spaces, being hit by flying objects, caught in explosions, hurt by collapsing machinery, falling from heights and tripping on obstacles.

Biological hazards (biohazards)

Biohazards refer to biological substances that pose a harm to the health of living organisms. Sources of biological hazards may include insects, bacteria, fungi, plants, worms, animals and viruses. These sources can cause a variety of health effects ranging from skin irritation and allergies to infections, cancer and so on. 

Ergonomic hazards

Ergonomic hazards refer to workplace conditions that pose the risk of injury to the musculoskeletal system of the worker. These injuries can be caused by performing repetitive and forceful movements and awkward postures that arise from improper work methods and improperly designed workstations, tools, and equipment.

Noise hazards

Excessive noise can disrupt concentration, interfere with communication and result in loss of hearing. High impact noises are particularly damaging. Noise can also mask out signals and affecting communication with others.

Hazard Analysis Procedure

• Examine the job and determine the components
• Identify tasks likely to present hazards
• Identify and assess hazards
• Determine and devise controls measures
• Develop safe work procedures if hazards cannot be eliminated

Hazard analysis methods

• Process Hazard Analysis (PHA)
• Event Tree Analysis
• Failure Modes and Effect Analysis
• Fault Tree Analysis
• Cause-consequence Diagram
• Hazard and Operability Studies(HaZOp)

Risk 

Risk is usually defined as the combination of the severity and probability of an event. In other words, how often can it happen and how bad is it when it does happen? Risk can be evaluated qualitatively or quantitatively.

Roughly: Risk = Frequency x Consequence of hazard

Risk can be evaluated qualitatively or quantitatively.

The qualitative approach requires that we describe risk in descriptive terms such as “high” or “low’ or “moderate”.

These terms are only effective if everyone has a good understanding of what they mean in the context of use. Hence a “high risk neighborhood” is not popular with insurance companies. If the terms are well defined or “calibrated” against a scale of values that is generally accepted the qualitative risk measurement can be very effective.

Figure shows that risk levels can be regarded as similar if a severe consequence may occur rarely or if a less severe consequence occurs more often.

It follows that risk reduction can be achieved either by reducing the frequency (likelihood) of the hazardous event or by reducing the consequences.

Usually a functional safety system acts to reduce the likelihood of the hazardous event whilst other operational measures are used to minimize consequences.

For example a blast proof wall may protect people against an explosion but it will not reduce the chances of the explosion.

So the easiest way to visualize an SIS providing safety is to regard it as reducing the event frequency