PROCEDURE FOR THE SAFE HANDLING AND USE OF SODIUM AZIDE

FROM NORTHEASTERN UNIVERSITY


I. INTRODUCTION

Sodium Azide, NaN3, mol wt 65.02, CAS Number 26628-22-8, is a colorless, odorless, crystalline solid (salt-like) or solution. It is soluble in water or liquid ammonia, slightly soluble in alcohols, and insoluble in ether. It is highly toxic and presents a severe explosion risk when shocked or heated. When heated from 275 to 330°C in dry air, the solid crystals decompose with the evolution of nitrogen gas, leaving a residue of sodium oxide. Sodium hydroxide then forms in moist air. Synonyms and Trade Names are Azide, Azium, and Sodium salt of hydrazoic acid.

 

2. PROPERTIES

Sodium azide is a common preservative of samples and stock solutions in laboratories and a useful reagent in synthetic work. It is not explosive except when heated near its decomposition temperature (300°C) or reacted with metals; heating sodium azide should be avoided. Sodium azide (solid or concentrated solution) should never be flushed down the drain since this practice can cause serious incidents when the azide reacts with lead or copper in the drain lines and explodes. Sodium azide has high acute toxicity as well as high toxicity to bacteria in water treatment plants.

Note that metal shelves and other metal items used to handle sodium azide (i.e., spatulas) can also result in the formation of heavy metal azides and thus should be avoided. Solutions of sodium azide do not pose the danger of shock-sensitivity associated with the solid form; however, the hydrazoic acid generated when the sodium azide is dissolved is extremely toxic. Therefore, the solution is should prepared inside a laboratory chemical hood. If not dissolved, solid sodium azide should be stored in a secured cabinet because of the shock hazardous.

 

3. HAZARDS

 

Sodium azide is on the Hazardous Substance List because it is cited by ACGIH, DOT, NIOSH, HHAG, DEP, and EPA (see Laboratory Chemical Hygiene Plan section 5 for glossary of terms). This substance also is on the Special Health Hazard Substance List because it is a mutagen. Mutagens may have a cancer risk. All contact with this substance should be reduced to the lowest possible level.

Sodium azide and hydrazoic acid (HN3, which is formed from NaN3 in water) are known to produce hypotension (low blood pressure) in laboratory animals and humans, and to form strong complexes with hemoglobin, and consequently block oxygen transport in the blood.

Acute inhalation of HN3 vapor by humans results in lowered blood pressure, bronchitis, eye, nose, throat, and lung irritation, headache, weakness, and collapse. A skin designation has been assigned to the OSHA PEL due to the ability of NaN3 to readily penetrate intact skin, and any dermal exposure can significantly contribute to the overall exposure to sodium azide.

Target organs are eyes, skin, lungs, central nervous system, cardiovascular system and kidneys. Use appropriate ventilation (laboratory chemical hood) and personal protective equipment (such as gloves) to minimize potential exposure.

 

4. WORKPLACE EXPOSURE LIMITS

NIOSH: The recommended airborne exposure limit is 0.11 ppm as hydrazoic acid or 0.3 mg/m3 as sodium azide, which should not be exceeded at any time.

ACGIH: The recommended airborne exposure limit is 0.11 ppm as hydrazoic acid or 0.29 mg/m3 as sodium azide (0.1 ppm Ceiling, Skin), which should not be exceeded at any time.

The above exposure limits are for air levels only. When skin contact also occurs, you may be overexposed, even though air levels are less than the limits listed above.

 

5. HANDLING AND STORAGE

  • Prior to working with sodium azide you should be trained on its proper handling and storage. Use appropriate personal protective equipment such as safety glasses, goggles, gloves, and laboratory coat when handling sodium azide.

  • On contact with water, sodium azide forms hydrazoic acid which is toxic.

  • Sodium azide reacts with heavy metals (such as silver, gold, lead, copper, brass, or solder in plumbing systems); and metal salts to form an accumulation of the highly explosive compounds such as lead azide and copper azide.

  • Sodium azide is not compatible with chromyl chloride, hydrazine; bromine; carbon disulfide; dimethyl sulfate; and dibromomalonitrile; strong acids (such as hydrochloric, sulfuric and nitric); and acid chlorides.

  • A danger of explosion exists from friction, heat or shock.

  • Store in tightly closed containers in a secured, cool, and well-ventilated area away from water.

6. DEACTIVATION OF SODIUM AZIDE

Sodium azide is among the P-listed hazardous wastes regulated by the US Environmental Protection Agency. As a discarded commercial chemical product, off specification species, container residues or spill clean up material, it must be managed as a hazardous waste. Dilute solutions (5% or less) managed as part of your experiment protocol can be destroyed by reaction with nitrous acid, which is freshly prepared. Massachusetts regulations do not allow sodium azide to be deactivated (treated) outside your experiment and away from the point of generation.

2NaNO2 + H2SO4 ® 2HNO2 + Na2SO4
2NaN3 + 2HNO2 ® 3N2 + 2NO + 2NaOH

The operation must be carried out in a chemical hood due to the formation of nitric oxide. An aqueous solution containing no more than 5% sodium azide is put into a three-necked flask equipped with a stirrer, a dropping funnel, and an outlet with plastic tubing to carry nitrogen oxides to the laboratory chemical hood flue. A 20% aqueous solution of sodium nitrite containing 1.5 g (about 40% excess) of sodium nitrite per gram of sodium azide is added with stirring. A 20% aqueous solution of sulfuric acid is then added gradually until the reaction mixture is acidic to pH paper.

Caution: This order of addition is essential. If the acid is added before the nitrite, poisonous volatile HN3 will be evolved.) When the evolution of nitrogen oxides is over, the acidic solution is tested with starch-iodide paper; if it turns blue, it means that excess nitrite is present and decomposition is complete. The reaction mixture can safely be washed down the drain. Note that the solution must be neutralized with dilute NaOH solution to pH 6-9 prior to discharge.

All personnel involved in deactivating sodium azide shall conduct inspections, maintenance or other activities to ensure that the process does not result in spills, leaks, or emissions into the environment prior to deactivation of the material.

Sink disposal of solutions of azide compounds that have not been deactivated should be avoided whenever possible. If some does get down the drain it is important copious amounts of water are flushed down to avoid accumulation of explosive deposits. Avoid contact with acids.

 

7. DETECTION AND DISPOSAL OF SODIUM AZIDE

The following colorimetric testing can be used to detect NaN3 in your used solution: A drop of the solution is placed in the depression of a spot plate and treated with 1 or 2 drops of dilute hydrochloric acid. A drop of ferric chloride solution is added and the spot plate gently heated. A red color indicates hydrazoic acid and thus the presence of sodium azide in the solution.

 

8. FIRST AID

If your eye or skin is exposed to NaN3 or HN3, use the emergency eye wash to immediately flush with large amounts of water for 15 minutes and then seek medical attention. If you swallow or inhale NaN3, seek medical attention immediately. A medical emergency is needed with severe shortness of breath.