What is an Explosive Environment?
What is explosive atmosphere? How is it formed? Which substances cause it?
Explosive atmosphere is defined in the ATEX 2014/34/EU directive and related regulations as “the mixture of gas, vapor, mist and dust of flammable substances with air under atmospheric conditions and which can completely burn in contact with any ignition source”. Environments with flammable, explosive gases, dust and vapors are among the high-risk areas in industrial facilities.
Which conditions must be present for combustion and explosion to occur in an environment?
As can be understood from the definition, 3 basic components must be together in order to create a risk of fire-explosion in an environment.
These three components are:
⦁ Combustible material (gas, steam, dust, etc.)
⦁ Oxygen (for combustion to occur)
⦁ Ignition source (spark, flame, very hot surface, etc.)
These three components constitute the definition of fire triangle in the literature.All security measures are designed to prevent these three components from coming together. Any environment where this triangle does not occur is considered as a safe environment against combustion and explosion.
What are flammable materials? How do they make the environment explosive?
We can basically divide flammable materials into three groups; flammable gases, flammable liquids, flammable dusts.
Explosion in environments with flammable, combustible and explosive gases is related to the ratio of the flammable gas to the ambient air. If there is too little or too much flammable gas in the environment, combustion or explosion will not occur. The limits of this range in which the gases are flammable-explosive are called the lower explosion limit (LEL) and the upper explosive limit (UEL for short).
For example, the lower explosion limit of methane gas is 4.4% and the upper explosion limit is 17%. In an environment where methane gas leaks, when the amount of methane reaches 4.4%, it means that the environment has become explosive.
Flammable liquids with a low boiling point can evaporate easily. When such vapors reach a certain amount in the atmosphere of the environment they are in, combustion or explosion occurs if there is oxygen and a trigger energy source. The minimum and maximum explosion points of vapors of flammable liquids in the atmosphere are also called LEL and UEL. The most flammable liquids known to be encountered in many places are petroleum products such as gasoline, thinner, aviation fuel, diesel and solvent liquids used in a wide variety of industries.
Combustible dusts are volatile particles with flammable and explosive potential in various work areas. They have the potential to explode at normal temperatures and normal atmospheric pressure values. In various work areas, they can accumulate on the surfaces like a film layer, or dusts of 500µm and smaller can remain suspended in the air, creating an explosive atmosphere. Dusts are divided into flammable and non-flammable powders according to their flammable properties. According to their conductivity properties, they are divided into conductive (electrical resistivity 10,000Ωm or less) and non-conductive (electrical resistivity 10,000Ωm or higher).
To dust explosions:
⦁ Hot surfaces
⦁ Mechanical sparks
⦁ Incandescent metal particles
⦁ It can be caused by sources such as friction, static electricity.
The explosion triangle we encounter in gas explosions turns into an explosion pentagon in combustible dust. The factors that make up the explosion pentagon are:
⦁ Combustible dust
⦁ Suspended dust
⦁ A spark or an energy source