Chemical water-reactive

The characteristics of a chemical or substance that would categorize it as a reactive material include (1) it reacts violently with water, (2) it forms potentially explosive mixtures with water, or (3) when mixed widi water or other chemicals, it generates toxic gases, vapors or fumes in a quantity sufficient to present a danger to human health or the environment. Because water is the most common fire suppressant, the characteristic of reactivity is especially relevant since the application of water to eliminate or prevent the spread fires may be counterpro-ductive rather than helpful. Several categories of chemicals will be discussed from this standpoint however, several of these same chemicals also present additional hazards. 

Metals — Several metals react with water and air with the extent of reactivity being dependent upon the physical state of the metal. The highly reactive metals such as lithium, sodium, and potassium are pyrophoric (i.e., they ignite spontaneously in air without an ignition source). In contrast, the less reactive metals such as magnesium, zirconium, titanium, aluminum, and zinc, are highly pyrophoric only as dusts. 

Lithium, sodimn, and potassium (alkali metals) react rapidly with water to release hydrogen (H2) gas  

Sufficient heat is generated to ignite the hydrogen gas so that it can react explosively with the oxygen in air. Metals like magnesium, aluminum, titanium, and zirconium in pure form also react with water to release H2, but heat must be supplied to initiate the reaction. The generalized representation is  

Hydrides — True hydrides (i.e., those in which the hydrogen is in its anionic or most reduced form) are salt-like compounds in which the hydrogen is combined with alkali metals, either alone as simple hydrides or in association with other elements as complex hydrides. Hydrides react with water to release hydrogen. 

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Some Water-Reactive Chemicals (CCPS 1995b, NFPA 2002)... 

This is not an exhaustive list of water-reactive chemicals. See Table 3.4 for additional categories. 

Kapias, T., R. F. Griffiths, and C. Stefanidis (2001). "REACTPOOL a Code Implementing a New Multi-Compound Pool Model That Accounts for Chemical Reactions and Changing Composition for Spills of Water Reactive Chemicals." Journal of Hazardous Materials A81, 1-18. 

Occupational Safety and Health Administration (OSHA), 1996. Hazard Information Bulletin, Water Reactive Chemicals, Hazardous Materials Not Covered Under 29 CFR 1910.119, July 3, 1996. 

In the strict chemical sense, the term drying refers to removal of water present in solid or fluid materials by treatment with water-reactive chemicals. In a wider (chemical engineering) context, it also refers to use of physical methods to remove any unwanted liquids (or vapours) from solid, liquid or gaseous phases. 

Chemicals that are water or air reactive pose a significant fire hazard because they may generate large amounts of heat. These materials may be pyrophoric, that is, they ignite spontaneously on exposure to air. They may also react violently with water and certain other chemicals. Water-reactive chemicals include anhydrides, carbides, hydrides, and alkali metals (e.g., lithium, sodium, potassium). 

Listings of chemicals such as incompatible chemicals potentially explosive chemicals and reagent combinations water-reactive chemicals pyrophoric chemicals and peroxide-forming chemicals, including time limits on retention after opening the original container. 

Water reactive chemicals should be stored in a cool, dry place. 

Do not store water reactive chemicals under sinks or near water baths. 

Class D fire extinguishers for the specific water reactive chemical being stored should be made available. 

Water-reactive chemicals Store in dry, cool, location protect from water from fire sprinkler. Sodium metal, potassium metal, lithium metal, lithium aluminum hydride Separate from all aqueous solutions and oxidizers... 

Water reactive chemicals should be stored in a cool, dry place. Do not store water reactive chemicals under sinks or near water baths. 

This requirement is intended to protect water reactive chemicals from exposure to water in water based fire suppression systems that may be used where flammable liquids are stored. Spraying water on a water reactive material during an upset condition could increase the severity and danger of the upset condition. While not required, consideration should be given to applying a similar restriction in oxidizer storage areas. See section 4.4.2. 

Many reactions with water occur without incident. Other water-reactive chemicals can present a transportation risk because the reactions are violent, evolve high heat, or generate toxic, flammable, corrosive, or otherwise dangerous reaction products ... 

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