Laboratory Safety:Management of Reactive Chemicals

A number of relatively common chemicals and reagents can become explosive when stored improperly for excessive periods of time. The following policy provides a list of the most common potentially reactive/explosive hazardous chemicals and provides information on how to prevent explosive hazards.

1. Peroxide Forming Chemicals

A variety of chemicals can form highly explosive peroxide compounds as impurities when exposed to air over a period of time. This problem is most common in ethers, but also occurs in a variety of other organic compounds as well as in some alkali metals and amides. As a result, great care must be taken to prevent the formation of peroxides in these chemicals.

Preventing the formation of peroxides is dependent on careful inventory control of peroxide forming chemicals. Most peroxide forming chemicals are sold commercially with inhibitors to prevent the formation of the peroxides. These are effective until the container is first opened. After a container is opened, the chemical comes in contact with air and may begin to form peroxides. Therefore, there are two steps to prevent the hazards of peroxide formation.

The first step in preventing the formation of peroxides is to date all containers of peroxide forming chemicals with the date the container was first opened.

The second step is to dispose of the peroxide forming chemicals within six months of the date the container was first opened. Manufacturers often state warnings on their peroxide forming chemicals. In this case, the chemicals should be dated and disposed of in accordance with manufacturers recommendations if more restrictive that the six month disposal limit set by EHS.

The following list is composed of potentially reactive/explosive peroxide forming wastes:

2. Picric Acid and other Polynitroaromatic Compounds

Picric Acid is commonly used in labs and is relatively safe in the form which it is sold. It is ordinarily sold with 10% water added for stabilization. However, picric acid can become explosive when it is allowed to dry out or when it forms certain metal salts. The following steps should be taken to safely store picric acid:

STEP 1: Never allow picric acid to be stored in containers with metal caps or come in contact with any metal.

STEP 2: Check Picric Acid frequently to ensure it remains damp. Add water if needed.

STEP 3: Never attempt to open a bottle of old or very dry picric acid. Contact EHS if this occurs.

Contact EHS for handling and storage information if other polynitroaromatic compounds are used in your laboratory.

3. Tollen's Reagent

Tollen's Reagent (ammoniacal silver nitrate) can form highly explosive silver fulminate over time after it has been used. To avoid this problem, add dilute nitric acid to Tollen's Reagent immediately after use and contact EHS for disposal.

4. Sodium Azide

Sodium Azide may form highly explosive heavy metal azides if contaminated or used improperly. Disposal of sodium azide solutions to the sanitary sewer may cause the formation of lead or copper azide in the plumbing which could potentially cause a serious explosion. Sodium Azide should never be heated rapidly or stored in containers with metal components.

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