Hazardous substances that are a safety concern under normal circumstances can turn into an even greater hazard in a fire or release situation. If you are responding to emergencies involving hazardous substances, make sure you know the dangers of mixing certain materials.
Combining various chemicals can produce new chemicals with hazards very different from the original materials. In a spill situation, it is important to prevent incompatible materials from making contact with each other. Mixing incompatible materials can result in fires, explosions, release of gases, and other unintended outcomes.
Reactive with water
Some chemicals react violently when they contact water. Strong acids are one example. When responding to spills of these materials, note the presence of water in the area. In the event of a fire near these materials, be careful not to make the situation worse by applying water to the flames or chemicals.
Heat from nearby fire can increase the vapor pressure of materials in closed containers. Internal pressure can increase to the point that the tank or container ruptures violently. This can lead to explosive release of expanding vapor and boiling liquid, fireballs, projectiles, toxic clouds, or vapor cloud explosions. Gases or vapors may also be released through ruptured pipes or opened relief valves or devices.
Spill cleanup materials
Some chemical treatments used for spill cleanup, like lime or soda ash, neutralize spilled substances. Different chemical treatments are designed for specific hazardous substances. Be sure to use these products as directed. Follow the recommended sequence for application of cleanup materials to avoid unexpected and potentially harmful chemical reactions. For example, a chemical reaction may occur if you mix the spill control agents for acids and caustics.
Also, be sure to always use proper personal protective equipment. Some spill control agents applied to clothing can produce harmful heat from a chemical reaction.
When responding to fires, make sure you understand the proper use of available fire extinguishers. Using the wrong agent on a fire can make things worse.
Water may put out a fire of ordinary materials like wood or paper. However, using it on other types of fires (flammable liquids, grease, electrical fires, or combustible metals) can cause the flames to spread and create a greater hazard. If carbon dioxide is used on flammable metal fires, a dangerous chemical reaction can occur.
What is reactivity?
Reactivity refers to the ability of a substance to undergo chemical change, usually by mixing with another substance or by breaking down. A dangerous reaction can result from several situations. Known reactive hazards are generally noted on the safety data sheet for the material.
What can happen?
If mixed with or exposed to an incompatible material, reactive substances may:
- emit dangerous fumes,
- release flammable or toxic vapors,
- start runaway reactions (uncontrolled chain reactions), or
- rupture pipes or closed containers.
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