Highly Reactive Materials

Explosivity

 

is defined as the tendency of a system to undergo violent or explosive decomposition under appropriate conditions of reaction or initiation.

 

 

Recognizing Reactivity Hazards in the Laboratory

1. Chemical Structures That Should Serve as Warning Signs

Though it is not possible to give an exact list of chemical components that will be explosive, it is possible to specify some general structural features that are often associated with high levels of reactivity or instability. These can be described based on a specific chemical group or on the bonding systems seen in the various molecular structures. Chemical names that include in part names such per-, peroxy, azo- and cetylide should cause you to consider the possibility of fragile bonds of peroxides, azides and acetylides. Another warning sign is an organic molecule with a large amount of bonded oxygen which could lead to a large volume release of gas and energy on decomposition.

Many examples of functional groups which have been shown to exhibit a certain level of instability and/or unusual reactivity are listed in Bretherick's book Chemical Reactivity and a modified version is given in the following table.

Compounds Containing Carbon


      
    
        
  • C=C-C=C dienes 
    • 
        
  • C=C=C allenes 
    • 
        
  • triple bonded carbons alkenynes, alkynes, haloalkynes, polyalkynes 
        
    • 
      

      



      
Compounds Containing Carbon and Nitrogen

      
    
        
  • C-N=N-C azo compounds 
    • 
        
  • C linking N rings triazoles, aziridines, nitriles, diaziridines 
    • 
        
  • CN2 diazo compounds 
    • 
        
  • C-N3 alkyl, aryl azides 
    • 
        
  • C-N=N-N triazenes 
    • 
        
  • C triple bond N dicyanogen 
    • 
      

      



      
Compounds Containing Carbon and Oxygen

      
    
        
  • C linking O rings oxiranes 
    • 
        
  • C-O-OH alkyl hydroperoxides 
    • 
        
  • (-CMe2O-O-)3 trimeric acetone peroxide 
    • 
        
  • C-O-O-C dialkyl peroxides 
    • 
      

      



      
Compounds Containing Carbon, Nitrogen and Oxygen

      
    
        
  • C-N=O nitroso compounds 
    • 
        
  • C-NO2 nitro compounds 
    • 
        
  • C-O-NO2 alkyl nitrites 
    • 
        
  • C-O-NO2 alkyl nitrates 
    • 
        
  • C=NOH oximes 
    • 
        
  • C-N=N-O- arenediazoates, bis(arenediazo) oxides 
    • 
        
  • C(NO2)2 gem-polynitroalkyl compounds 
        
    • 
        
  • CO.O-N=O acyl nitrites 
    • 
        
  • CO.O-NO2 acyl nitrates 
    • 
        
  • -C triple bond N--O nitrile oxides 
    • 
      

      



      
Compounds Containing Nitrogen and Oxygen

      
    
        
  • NO nitrogen oxide 
    • 
        
  • NO2 or N2O4 dinitrogen tetroxide 
        
    • 
        
  • H2NOH hydroxylamine and salts 
    • 
        
  • N2O dinitrogen oxide 
    • 
        
  • N2O5 dinitrogen pentoxide 
    • 
      

      



      
Compounds Containing Nitrogen and Other Elements

      
    
        
  • N-X N-halogen compounds 
    • 
        
  • N-metal N-heavy metal compounds 
    • 
        
  • -NF2 difluoroamino compounds 
    • 
        
  • -N-S- nitrogen-sulfur compounds 
    • 
      

      



      
Compounds Containing Halogens, Oxygen, and Other Elements

      
    
        
  • -O-X hypohalites 
    • 
        
  • -O-X-O2 halates 
    • 
        
  • N-Cl-O3 perchlorylamide salts 
    • 
        
  • O-X-O halites, halogen oxides 
    • 
        
  • O-X-O3 perhalates, halogen oxides 
    • 
      

      
Another group of compounds which has been described by Bretherick as 
        treacherously explosive are those which contain a nitrogenous ligand coordinated 
        to a metal, and a coordinated or ionic oxidizing groups (nitro, nitrate, 
        nitrite, perchlorate, permanganate, etc.). Examples of this category of 
        explosives include tetraamminecadmium permanganate, dipyridinesilver perchlorate 
        and bis-1,2-diaminoethanedintirocobalt(III) iodate. 

      

      
2. Using Chemical Labels as an Aid

      
As an aid in identifying the chemicals which pose a reactivity hazard 
        in the laboratory, all chemical manufacturers are required to include 
        relevant information on the chemical label. One of the most common grading 
        systems is that developed by the National Fire Protection Association (NFPA). In this system, 
        chemicals are rated from 0 (least reactive) to 4 (most reactive). It is 
        important for all laboratory personnel to recognize and become familiar 
        with the NFPA diamond and understand the grading levels established by 
        the NFPA for reactive materials. The yellow portion of the diamond gives 
        an indication of the reactivity of the material. 

      

      
NFPA System for Rating the Reactivity of Chemicals

      

      
 
        

          

            
      Rating  	Susceptibility to Release of Energy

	0	Normally stable materials, even under fire conditions.  	
		Do not react with water.

	1	Normally stable materials which may become unstable 	
		under fire conditions or at elevated temperatures or 	
		pressures.  May react with water, but not violently.

	2	Materials which are normally unstable and readily 	
		undergo violent chemical change but do not detonate.  	
		Includes materials which react violently with water, and 	
		other materials which undergo chemical change at normal 	
		temperatures and pressures and violent reaction at 	
		elevated temperatures and pressures.

	3	Materials which are capable of detonation, but require a 	
		strong initiating source or which must be heated under 	
		confinement before initiation.  Includes materials which 	
		are sensitive to thermal or mechanical shock at elevated 	
		temperatures and pressures.  Also includes those 		
		materials which react explosively with water without heat 	
		or confinement.

	4	Materials which in themselves are readily capable of 	
		detonation or explosive reaction at normal temperatures 	
		and pressures.  Includes materials which are sensitive to 	
		mechanical or localized thermal shock. 


          

        

      

      


      

      

      


      

      
Examples of Reactive Materials

      
Reactive materials are solids, liquids or gaseous materials 
        that exhibit any of the following properties:

      
 
        
The material is normally unstable and readily undergoes violent change 
          without detonating. 

        
Examples are materials that are capable of polymerization 
          reactions, such as polyvinyl benzene. 

        
The material is (water reactive) 
          and reacts violently or explosively with water. 

        
Examples include the alkali metals and many hydrides. 

        
The material is (pyrophoric), that 
          is, it self-ignites in the presence of air . 

        
Examples include diethylzinc and triethylaluminum, and many organometallic 
          compounds. 

        
The material, when contaminated or decomposed, becomes unstable and 
          is readily capable of undergoing violent change and/or detonating. 

        
Examples include peroxide forming 
          materials and reactions involving explosive combinations of incompatible 
          materials. 

        
The material is capable of detonation or violent reaction if subjected 
          to a strong initiating force or heated under confinement. 

        
This includes all materials with an NFPA reactivity rating of 3, including 
          those materials which are shock sensitive 
          at elevated temperatures and pressures. 

        
The material is capable of detonation at standard pressure and temperature. 
        

        
This includes all highly reactive chemicals 
          with an NFPA reactivity rating of 4. 

        
The material has been rated as extremely dangerous. 

        
The material is classified as a Forbidden 
          explosive, a Class A explosive, a Class 
          B explosive or a Class C explosive. 
        

      

      

      


        

      

      

      
Precautionary Measures to be Followed 
        When Using Reactive Chemicals

      
1. Reducing the Reactivity

      
Oftentimes the reactivity of a material can be reduced by inhibiting 
        the chemical process. The following table provides examples of reactive 
        materials and the mechanism that can be employed to reduce the reactivity. 
      

      

      
 
        

          
    
          

        

        

          

            
	   Reactive Material 	       Inhibitor 
            Picric acid 		Water 
            Methyl vinyl ether 		Triethanolamine 
            Cyclonite 			Beeswax 
            Lead azide 			Water 
            Lead styphnate 		Water 
            Acrylaldehyde 		Hydroquinone 
            Disodium acetylide 		Water 
            Methyl methacrylate 	Hydroquinone 
            Vinyl chloride 		Phenol 
            Tetrafluoroethylene 	Alpha terpinene 
            Chlorotrifluoroethylene 	Tributylamine 
        
    

          

        

      

      
2. Risk Management

      
The use of highly reactive materials cannot always be avoided. In these 
        cases, every effort must be made to reduce the risk to the lowest possible 
        level. The following precautionary measures are recommended whenever reactive 
        materials must be stored. 
      
    
        
  1. Isolate reactive chemicals. Store them away from other chemical classes. 
        
    2. 
        
  2. Have a nearby water source unless the chemicals are also water reactive. 
        
    3. 
        
  3. For water sensitive materials, make certain they are stored in a water-tight, 
          well marked cabinet. 
    4. 
        
  4. In general, store reactives in cool, dry area, away from direct sunlight. 
        
    5. 
        
  5. On the container label, indicate when the material was received, when 
          it was opened and when it should be considered expired. 
    6. 
        
  6. Protect all reactives from sources of shock, friction or grinding. 
        
    7. 
        
  7. Strictly limit the amount of reactives that are on hand. 
    8. 
      

      
 

      
3. Personal Protection

      
The protection of laboratory personnel from the effects of reactive or 
        unstable materials, and their reaction systems, should be the primary 
        consideration of the principal investigator. Of greatest importance is 
        the need for detailed instruction and training in the use of reactive 
        materials, as is required by Federal, State and 
        University guidelines. In addition, appropriate protective devices 
        must be provided. This includes the following items to be used as needed: 
      
    
        
  • Bench explosion shields 
    • 
        
  • Safety glasses designed for impact resistance 
    • 
        
  • A face shield with snap on throat protector 
    • 
        
  • Gloves for when it is necessary to reach around the shield to manipulate 
          equipment 
    • 
        
  • Laboratory coats made of flame resistant material 
    • 
        
  • Bomb bays and remote control equipment for especially dangerous reactions 
        
    • 
      

      


        

      

      

      


        

      
 Created and maintained by Nancy Magnussen

      last revised 2 Aug 1997

      nancy@isc.tamu.edu 

      


        

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Copyright © 1996 by College 
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