Azides heavy metal, explosive hazards

The majority of the metal azides are sensitive explosives and exposure to heat, friction or impact is usually undesirable. Contact of most azides, particularly readily soluble ones, with acids will produce hydrogen azide, itself an explosive and highly toxic low-boiling liquid. In presence of heavy metals, it may give other equally hazardous heavy metal azides. These may also be formed from contact of soluble azides with heavy metals. 

An approach applicable to any scale of operation is to recognize not only direct hazards due to the explosivity of explosive azides, but also the indirect hazards resulting mainly from hydrolysis. Hydrolysis gives hydrazoic acid, HN3, a toxic substance which is physiologically very active and is also the medium by which very sensitive heavy-metal azides, most notably copper azide, can be formed. 

AZIDA de BARIO (Spanish) (18810-58-7) Highly unstable in dry form. Dust forms explosive mixture with air. Heat, shock, or friction can cause spontaneous decomposition and explosion. Forms shock-sensitive mixtures with lead and other heavy metals. Contact with barium, iron, or sodium will increase its sensitivity to explosion. Contact with acids forms corrosive hydrogen azide. Reacts violently with oxidizers, carbon disulfide. Commercially available in ethyl alcohol. Keeping the chemical wet greatly reduces its explosion hazard. 

Apart from being able to better compare observed with theoretical detonation properties, it would appear profitable to carry out refined C-J calculations on heavy-metal azides and other detonator compounds to determine whether the correlations noted earlier indeed exist. (They relate computed explosion temperatures to sensitivity, and C-J pressures to detonator effectiveness.) If the correlations can be substantiated, there appears to be merit in performing C-J calculations on multicomponent detonator mixes in order to predict the optimum composition for minimum sensitiveness and maximum effectiveness. Thus hazardous empirical testing would be held to a minimum. 

Azides react explosively or form other explosive azides when they come in contact with a number of substances. With acids, almost all metal azides react to form hydrazoic acid, which is dangerously sensitive to heat, friction or impact. Azides can react with salt solutions of many metals forming azides of those metals, some of which—especially, the heavy metal azides—are highly sensitive to friction and impact. The rates and yields of such reaction products would depend on the equilibrium constants and solubility products. For example, soluble alkali-metal azides can readily form lead or cadmium azide when mixed with a salt solution of lead or cadmium. The hazardous properties of some of the compounds of this class are discussed below. 

The decreasiug pattern above is of little practical iuterest, however, as all the heavy metal azides detouate violeutly upou heatiug aud mechauical impact. Table 33.1 lists the heat of formatiou AHf(s) for some azides. It may be seeu that explosivity decreases with a decrease of AH° and at a low value of +16.8 kcal/mol, sodium azide is nonexplosive. Discussed below are individual compounds of commercial interest or those presenting severe explosion hazard. The explosive properties of additional compounds are highlighted in Table 33.2. 

Both azides can readily form explosive products when combined with acids, halogens, halogen oxides, ammonia, or heavy metal salt solutions. Cupric azide has limited use as a powerful initiator. It is a DOT-classified forbidden substance Hazard Label Forbidden. 

There are other compounds that, when used in the laboratory, can also produce serious hazards for maintenance workers if not disposed of properly. Sodium azide is often used as a preservative for laboratory water to prevent formation of bacteria. However, if poured down the sink, the azide can react with brass, copper, or lead in the piping to produce heavy metal azides—highly explosive compounds. Maintenance workers and plumbers have been injured while working on laboratory sinks from inappropriate disposal of azides into laboratory sinks. 

While the use of silver azide has been recommended in some syntheses, in most cases this does not appear to be necessary. In view of the explosive hazards associated with heavy metal azides, use of this azide is best avoided. 

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