Inherently Safer Plants – Part I

“What you don’t have, can’t leak!”

These are the words of Mr Trevor Kletz, ICI and LU.

If you develop, operate and control a chemical process such that bad consequences are reduced, owing to different chemistry, chemicals, conditions or simplicity, wouldn’t the safety of the plant be improved? Is this better than layers of protection? Prevention is better than cure.

The inherent safety structure consists of three parts:

1. Hazard Identification
2. Hazard Evaluation
3. Inherent Safety Evolution

A hazard is a physical or chemical characteristic that has the potential for causing harm to people, the environment or property. They are characteristic of the materials, chemistry and process variables.

Let’s see some of the hazards, relating them to their intensity of destruction.

• Acute toxicity: Chlorine is toxic by inhalation.
• Chronic toxicity: Sulfuric acid is extremely corrosive to skin. Nuclear material can cause chronic toxicity too.
• Flammability: Ethylene is flammable.
• Instability: High pressure confined steam contains a lot of energy.
• Extreme conditions: Styrene can polymerize releasing heat.

Air pollution, water pollution, ground water pollution, waste disposal are other  examples of consequences.

Representative list of types of hazards:

1. Fires: Flash fires, Pool fires, Jet fires. For example, ammonia, multi-bond hydrocarbons
2. Explosions: Vapor cloud explosion (VCE), Confined deflagration, Detonation, Pressure vessel rupture. For example, multi-bond hydrocarbons, epoxides, hydrides and hydrogen, metal acetylides, nitrogen compounds, oxygenated compounds of halogens, oxygenated manganese compounds, peroxides.
3. Toxicity: Environmentally (chronic, acute, individually toxic, broadly toxic), pesticides, fungicides, herbicides, insecticides, fumigants. For example, ammonia, chlorinated hydrocarbons, cyano compounds, polychlorinated biphenyls, poly-cyclic aromatic hydrocarbons.
4. Product: Customer injury, waste disposal

Are there other hazards associated with dangerously reactive chemicals?

Many dangerously reactive materials can also undergo dangerous reactions from direct contact with other and incompatible materials. Incompatibility hazards can be complicated. The chance of a dangerous reaction depends not just on the different combinations of chemicals involved, but it also depends on the amounts of each, the surrounding conditions such as temperature, and whether the substances are enclosed in a sealed container or not.

The SDS and the container labels should explain all of the hazards of the dangerously reactive liquids and solids that you work with.

Reactive combinations of chemicals:

• Acids + chlorates = spontaneous ignition
• Acids + cyanides = Toxic/flammable gas
• Acids + fluorides = Toxic gas
• Acids + epoxides = Heat/Polymerization
• Alkali + nitro compounds = Easy to ignite
• Alkali + nitroso compounds = Easy to ignite
• Ammonium salts of alkali metals + chlorates = Explosive salts
• Ammonium salts of alkali metals + nitrates = Explosive salts
• Ammonium salts of alkali metals + alcohols = Flammable gas
• Ammonium salts of alkali metals + glycols = Flammable gas
• Ammonium salts of alkali metals + amides = Flammable gas
• Ammonium salts of alkali metals + amines = Flammable gas
• Ammonium salts of alkali metals + azo compounds = Flammable gas
• Ammonium salts of alkali metals + diazo compounds = Flammable gas
• Inorganic sulfide metals + water = Toxic/Flammable gas
• Inorganic sulfide metals + explosives = Heat/Explosives
• Inorganic sulfide metals + Polymerizable compounds = Polymerization

Read more:

• Principles of Inherent Safe Design
• Reactive Chemical List
• Storage and Proper Segregation of Chemical Classes

Reference:

Dangerously Reactive Liquids and Solids – Hazards

Last Edited: January 8 2018