About Fires and Explosions

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About Fires and Explosions

Destructive fires are the nightmares of planners, installation technicians, and operators of systems with potentially explosive atmospheres. Not only the purview of the chemical and petrochemical industries, explosion protection is also of concern to seemingly innocuous industries. Be safe with flameproof and explosion proof electrical components.

Every January 8th is “Show and Tell at Work Day”. Today we are going to do a show and tell about how explosions occur so that you understand the particular risks involved. This awareness will help to ensure the safety of your people and achieve a fault-free and a safe production process.

Complete Combustion

A fast oxidation process, a destructive fire or complete combustion occurs when a combustible material is decomposed exothermally where there is a sufficient supply of oxygen. As the fire spreads faster and faster, so deflagration, explosion and, in extreme cases, detonation can occur respectively.

The damage caused by complete combustion increases in direct proportion to the speed at which the fire is spreading.

Magnitude of propagation velocity:
Deflagration cm/s
Explosion m/s
Detonation km/s

How Explosions Occur

An explosion can only occur the trio of a combustible material, oxygen, and a source of ignition are present. If one component is missing, no exothermal reaction will occur.

Potentially Explosive Materials

If their particle size is less than 1mm, combustible materials such as vapours and dusts are referred to as potentially explosive. (The vapours, aerosols, and dusts which occur in practice have a particle size of between 0.001 mm and 0.1 mm.)

If a potentially explosive material is combined with oxygen, a potentially explosive atmosphere is created.

The concentration of gasses are calculated to determine the possibility of an explosion. The mixture can only be ignited if the concentration of the material in air is within the lower (LEL) and upper (UEL) explosive limits.

The upper explosive limit (UEL) changes to 100 percent by volume. The explosive range of a material extends as the pressure and temperature rise.

Similar specifications can be made for dusts as for gases, even if the explosive limits do not have the same meaning here. Clouds of dust are generally inhomogeneous and the concentration within the same cloud will fluctuate sharply. A lower flammability limit (of approximately 20…60 g/m3 ) and an upper flammability limit (of approximately 2…6 kg/m3 ) can be determined for dusts.

What To Watch Out For

Having an overview of what is a source of ignition, and what causes it, can help you to reduce your risk of explosion.

Source of ignition Examples of causes
Adiabatic compression and shock waves Sudden opening of valves
Arcs Short circuit, switching operations
Electrical compensating currents, cathodic anti-corrosion protection Reverse currents from generators, short circuit to exposed conductive part or ground fault, induction
Electrical systems Opening or closing of contacts, loose contacts.

A PELV (U<50V) is not an explosion protection measure. Even low voltages can generate sufficient energy to ignite a potentially explosive atmosphere.

Electromagnetic waves in the 3 x 1011 – 3 x 1015 Hz range Laser beam for distance measurement, especially for focusing
Exothermal reactions Chemical reactions lead to heat production
Flames and hot gasses Combustion reactions, heating up during operation
High frequency 104 – 3 x 1012 Hz Wireless signals, industrial high-frequency generators for heating, drying, or cutting
Hot surfaces Heater, metal-cutting, heating up during operation
Ionizing radiation X-ray apparatus, radioactive material, absorption of energy leads to heating up
Lightning strike Atmospheric weather disturbances
Sparks Mechanically created sparks caused by friction, impact, or abrasion, electric sparks
Static electricity Discharge of charged, separately-arranged conductive parts
Ultrasound Adsorption of energy in solid or liquid materials leads to heat production

Flameproof Manufacturing

For safety in a hazardous area (Zone 1 and Zone 2; Zone 21 and Zone 22), order your flameproof and explosion proof electrical components today. +27 11 9718 7810 or questions@flameproofmanufacturing.com

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