The Explosive Truth.
It is important that operators in hazardous locations ensure that their personnel are educated as to the dangers of explosions in their workplace. A joint effort by the manufacturers of explosion-proof electrical equipment and the constructors and operators of industrial plants can help ensure the safe operation of electrical equipment in hazardous locations.
What is a hazardous Area?
Hazardous areas are locations where flammable liquids, gases or vapors or combustible dusts exist in sufficient quantities to produce an explosion or fire. In hazardous areas, specially designed equipment and special installation techniques must be used to protect against the explosive and flammable potential of these substances.
Hazardous locations can also be described as those locations where electrical equipment might be installed and which, by their nature, might present a condition which could become explosive if the elements for ignition are present.
What is an explosion?
An explosion is defined as a sudden reaction involving rapid physical or chemical decay accompanied by an increase in temperature or pressure or both.
Explosions can cause substantial loss of life and damage to the physical environment.
When will an explosion occur?
The most common types of reaction are between flammable gases, vapors, or dust with oxygen contained in the surrounding air.
As a rule, three basic requirements must be met for an explosion to take place in atmospheric air:
1. Flammable substance — needs to be present in sufficient quantity to produce anignitable or explosive mixture.
2. Oxidizer — must be present in sufficient quantity in combination with the flammable substance to produce an explosive mixture. Most common is air (O2).
3. Source of ignition — a spark or high heat must be present.
The presence of these three elements make up the sides of the ignition triangle. If any one of the three elements is missing, an explosion will not occur. All three elements must exist simultaneously for an explosion to occur.
Flammable Substance
Flammable substances can be divided into three subgroups:
? Flammable gas
? Flammable liquids/vapors
? Flammable solids
Oxidizer
The oxidizer referred to in all common hazardous location standards and explosion-proof equipment is air at normal atmospheric conditions.
Ignition Source
? Open flames
? Hot gas
? Chemical reactions or biological processes which occur spontaneously at certain oxygen levels or temperatures
? Lightning
? Intense electromagnetic radiation
? Ionizing radiation
? Adiabatic compression and shock waves
? Static electricity
? Sparks or arcs from electrical equipment or wiring
? Hot surfaces of electrical equipment or wiring
Where do explosions most frequently occur?
Explosion hazards typically exist in chemical plants, refineries, paint shops, cleaning facilities, mills, flour silos, tanks, and loading facilities for flammable gases, liquids, and solids.
How are explosion hazards controlled?
Reduction of hazards is not absolute. There is no absolute safety. Removing one of the elements from the ignition triangle can provide explosion protection and preclude unwanted, uncontrolled, and often disastrous explosions. If one of the three elements of the ignition triangle is missing, ignition will not occur. Since flammable substance and
oxidizers cannot be frequently eliminated with certainty, inhibiting ignition of a potentially explosive atmosphere can eliminate danger at the source.
Principles for ensuring that electrical equipment does not become a source of ignition
The objective of selecting an electrical apparatus and the means of installation is to reduce the hazard of the electrical apparatus to an acceptable level.
Four principles ensure that electrical equipment does not become a source of ignition. The basic point is to ensure that parts to which a potentially explosive atmosphere has free access do not become hot enough to ignite an explosive mixture.
