Many hazardous chemicals and dangerous goods have incompatibility hazards. An incompatibility hazard is the potential for incompatible substances (which come in contact with one another) to create a dangerous reaction.
Fires, explosions, the release of toxic, corrosive or flammable vapours, are all dangerous reactions that can be caused by the mixing of incompatible chemicals. To help with your hazard identification and risk assessment process, this blog looks at different factors which influence chemical compatibility.
The first type of incompatibility hazard occurs when incompatible substances contact one another, when either deliberately mixed by a worker or during a spill.
1. Chemicals mixed by workers
When workers mix two or more highly reactive chemicals together in error the result can be a catastrophic fire, explosion or release of toxic gases. Many workplace accidents and dangerous incidents occur when workers don’t understand incompatibility hazards or when substances haven’t been labelled or stored correctly. This is certainly true in the example below, could this happen at your workplace?
REAL WORLD EXAMPLE: Two containers of chemicals at a water treatment plant were stored next to one another. One drum contained the chemical sodium bisulfate and in the other, sodium hypochlorite (a type of bleach). These two substances are incompatible. A group of workers noticed the drum of sodium bisulfate was low and needed filling. By mistake, one worker began filling the bisulfate drum with bleach, causing a violent reaction. The chemical drum ruptured and sprayed two workers with chemicals as well as releasing dangerous gases. Two workers received severe chemical burns and respiratory complications, three more (who helped decontaminate the area) were treated for respiratory difficulties.
2. Chemicals mixed during spillage or disposal
When two or more incompatible chemicals are spilled or mixed up during waste disposal they may produce flammable, toxic or corrosive gases/vapours. Chemical reactions like this can occur very quickly, but in many instances it takes a long time for the buildup of hazardous materials to create an emergency situation. Your risk assessment must always consider the way you dispose of hazardous waste.
REAL WORLD EXAMPLE: Workers required medical treatment for headaches, burning eyes, and chest pains when they were exposed to fumes coming up from a floor drain. A chemical reaction between sulphuric acid and photographic chemicals that had been poured down the drain created the dangerous fumes.
Many incompatibility hazards occur because of the container used to store the chemicals. Sometimes the containers or cabinets themselves are not suited to the hazard class of the chemical, at other times the container fails and the hazardous chemicals inside are released.
3. Chemicals stored in unsuitable containers
When carrying out your chemical hazard analysis and risk assessment you should pay close attention to the suitability of the containers and safety cabinets holding each of the substances. Use only containers constructed in full conformance with the Australian Standards and purpose-built for the hazard class of the chemical being stored. Avoid using makeshift cupboards and mixing vessels because it can be almost impossible to determine the chemical properties of the building materials and componentry.
REAL WORLD EXAMPLE: A worker was mixing cement in a waste ceramic shell. The worker didn’t realise the ceramic shell had been constructed using thorium oxide, which reacted with the cement as water was being added. The mixture became hot and began to release smoke and a fume of sulphuric acid. Approximately 9 workers were exposed to the fumes and some of them suffered irritation to the respiratory tract and lungs.
4. Containment structures degrading over time
Hazardous chemicals (particularly corrosives) will eventually degrade chemical safety cabinets and containment vessels. Your risk assessment should always factor in the guaranteed life-time of all containers, compounds, and storage cabinets.
REAL WORLD EXAMPLE: A steel process tank at a manufacturing plant collapsed and caused catastrophic damage on two adjacent worksites. On one of the worksites employees were injured and property was damaged, at the other worksite a customer was killed. A chemical manufacturing process involving sodium hydroxide was being carried out in a high-strength steel tank, but the materials in the coating used to protect the process tank from the corrosive chemicals had never been sufficiently tested for suitability. The coating eventually failed which led to stress corrosion and cracking in the tank. The tank collapsed violently, destroying the exterior building and propelling debris onto the two adjacent worksites.
5. Spilled chemicals damaging other chemical containers
During your risk assessment you should consider if chemicals released during a major or minor spill could damage or destroy the packaging materials or containers of other chemicals. This is critical if there is any chance of a corrosive chemicals being released or spilled.
Incompatible storage arrangements
Another type of incompatibility hazard is when hazardous substances are stored too close to flammable materials. Any resulting fire will be intensified by the chemicals or will set off other dangerous reactions.
6. Fire releases chemicals into the environment
When flammable or oxidising chemicals are stored next to toxic and corrosive substances, a fire in the area could cause the rapid dispersal of toxic gases and corrosives. Your risk assessment should consider how work operations like load packaged chemicals and warehouse transfers could impact other substances stored nearby.
REAL WORLD EXAMPLE: A fire broke out at a chemical warehouse when packages of oxidisers being transferred by forklift were dropped and ignited. The fire damaged chemical stores which released chlorine gas and fire fighters were exposed to the toxic fumes.
7. Fire/dangerous reaction impinges on chemical containers
Your risk assessment should consider the possibility of fires or other dangerous reactions damaging your chemical stores. You may need to ensure hazardous chemicals like compressed gases or aerosols are stored in cages with sufficient projectile protection, or liquid chemical containers have enough spill protection.
REAL WORLD EXAMPLE: A fire broke out on an upper level grate floor, this also caused an explosion. A chemical tank turned over during the explosion and spilled over an employee working on the floor directly below the grate. He was killed, and 2 other employees (who tried to help their co-worker) were hospitalised after exposure to chemical vapours.
8. Incompatible fire extinguishers
Even fire extinguishers can create incompatibility hazards. Suppression equipment installed to provide fire protection for one substance, may be incompatible with another chemical stored in the same area. Your risk assessment should carefully consider the chemical properties of the fire suppression foams and powders you have at the workplace.
Incompatibility hazards are complex and require a full risk assessment, and this blog has provided only a few examples. We suggest downloading our free eBook How to manage the risk of Hazardous Chemicals in the workplace to learn how to properly identify, assess, and control chemical risks and incompatibility hazards. Download and read it today by clicking on the image below: