Hazard is a physical event, which carries potential (an ability) to cause damage to people, property or the environment. Hazard is therefore frequently referred to as hazardous events. In energy facilities, such events include explosions, fire, releases of toxic or. noxious substances.

The extent of the hazardous event, which in everyday life is often referred to as an accident, is influenced by the following factors:

  • Size of stock
    The bigger the stock of hazardous substances in the process, the greater the risk.
  • Energy
    It is, for instance, contained in a chemical reaction or in the state of the substance, for example, a liquid at high pressure above its normal boiling point contains a lot of energy.
  • Time
    The hazard in the event of a toxic substance release depends on the speed of the release; time is also important with regard to taking emergency measures and the evacuation of people; what matters is the length of the interval between the first warning sign and the explosion or release.
  • Distance
    An important factor of hazard is the distance at which the accident can cause damage. In general, fire affects a small area, an explosion a larger area and a toxic substance release affects the largest area.
  • Emergency response
    The extent of the consequences caused by an accident is smaller if the exposure of people in the affected area is limited, which is achieved through appropriate actions and accident-specific measures.

Each hazardous event has its origin, which may be primary or secondary. Primary sources of hazardous events are factors or characteristics of the process that are hazardous in themselves, for example, the presence of hazardous substances and reactions, heat, pressure, oxygen, energy sources, ignition sources, the possibility of human error, mechanical failures, movement of people and components in the process, reducedvisibility… A example of a primary source is a mechanical failure of the safety valve on a pressure vessel, which may result in a hazardous event, such as a release of a toxic substance from the vessel if the fault has not been detected on time.

Secondary sources of hazardous events are the result of hazardous events caused by primary sources: fire and the spread of fire, explosion and a secondary explosion, release of hazardous substances, etc. An example of a secondary source is damage in the wall of a pressure vessel resulting from the shock wave of the explosion.

Primary sources of hazard are prevented by good planning, management and maintenance of the process. For secondary sources, it should be ensured that in case of a hazardous event, they are reduced to a minimum. Efficient and robust technical devices certainly help to ensure that.

The presence of hazardous substances is one of the most important sources of danger in processes. In accordance with the guidelines of the European Community, substances that are classified as hazardous substances have one or more of the following characteristics:

  • toxicity and health hazard (very toxic, toxic, harmful, carcinogenic, mutagens, toxic to reproduction, corrosive, irritant),
  • flammability (extremely flammable, highly flammable and flammable substances),
  • causing ignition,
  • explosiveness,
  • oxidising potential,
  • corrosiveness,
  • radioactivity.