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Sodium Azide

FACT SHEET #3
April 2020
REVISION: FOURTH

NORTHEASTERN UNIVERSITY PROCEDURE FOR THE SAFE HANDLING AND USE AND MANAGEMENT OF SODIUM AZIDE

INTRODUCTION

Sodium Azide, NaN3, mol wt 65.02, CAS Number 26628-22-8, is a colorless, odorless, crystalline solid (salt-like) or solution. Synonyms and Trade Names include Azide, Azium, and Sodium salt of hydrazoic acid. 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 it is heated from 275 to 330 degree Celsius in dry air, the solid crystals will violently decompose into nitrogen gas, leaving a residue of sodium oxide. Sodium hydroxide then forms due to the air’s moisture.

PROPERTIES

Sodium azide is a common preservative of samples and stock solutions in laboratories and a useful reagent in synthetic work. Though, there is a low explosion risk when it is in its aqueous form. Its solid form is very explosive when shocked or heated to 275 degrees Celsius. In addition, it is very reactive with acids, chlorides, certain metals and their salts: Lead, Copper, Zinc, Cadmium, and Nickel. When it is mixed with acids and metals, it could release hydrazoic acid, which is toxic.

Both its solid and aqueous forms should never be flushed down the drain. This practice can cause serious incidents when the azide reacts with lead or copper in the drain lines, causing an explosion. Even if explosions did not occur, its high toxicity could kill the bacteria in water treatment plants.

Note that metal shelves and other metal items (i.e., spatulas) can also result in the formation of heavy metal azides. Thus, these should be avoided. As mentioned, solutions of sodium azide do not pose the danger of explosions. However, the hydrazoic acid generated when the sodium azide is dissolved is extremely toxic. Therefore, the solution should always be prepared inside a laboratory chemical hood. If the sodium azide is in its solid form, it should be stored in a secured cabinet because of the nature of its hazard.

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

HAZARDS

  • Sodium azide is on the Hazardous Substance List because it is cited by ACGIH, DOT, NIOSH, HHAG, DEP, and EPA (seeLaboratory Chemical Hygiene Plan section 5 for glossary of terms). This substance is also on the Special Health Hazard Substance List because it is a mutagen. Therefore, all contact with this substance should be minimized.
  • Sodium azide and hydrazoic acid (HN3, which is formed from NaN3 in water) are known to causehypotension (low blood pressure) in animals and humans, and it forms strong complexes withhemoglobin, which ultimately blocks 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 beenassigned to the OSHA PEL due to the ability of NaN3 to readily penetrate skin, and any skinexposure 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 double gloves) to minimize potential exposure.

WORKPLACE EXPOSURE LIMITS

  • NIOSH: The recommended airborne exposure limit is 0.11 ppm as hydrazoic acid or 0.3 mg/m3as 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/m3as 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 when air levels are less than the limits listed above.

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.
    • A danger of explosion could be caused by friction, heat, or shock, so it should be stored in tightly closed containers in a secured, cool, and well-ventilated area away from water.

DEACTIVATION OF SODIUM AZIDE
Sodium azide is among the P-listed hazardous wastes regulated by the EPA. 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 pr otocol can be destroyed by reaction with nitrous acid.

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 arranged 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 HN3will be generated.

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 is then presumably safe enough to be washed down the drain. However, you should treat any chemical as a hazardous waste as though they are not, so it should be poured into a hazardous waste container instead. Note that the solution must be neutralized with dilute NaOH solution to pH 6-9 prior to disposal.

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, please flush copious amounts of water to avoid accumulation of explosive deposits.

DETECTION AND DISPOSAL OF SODIUM AZIDE
The following colorimetric testing can be used to detect sodium azide (NaN3) in your used solution: adrop of the solution is placed in the depression of a spot plate and treated with 1-2 drops of dilute hydrochloric acid and 1 drop of ferric chloride solution. Let the spot plate be gently heated. If the mixture turns red, it is an indication of the presence of hydrazoic acid, which means that sodium azide is in the solution.

FIRST AID
If your eye or skin is exposed to sodium azide (NaN3) or hydrazoic acid (HN3), use the emergency eye wash to rinse your eyes for 15 minutes and then seek medical attention. If you swallow or inhale NaN3, seek medical attention immediately; medical emergency is needed with severe shortness of breath.

QUESTIONS
If you have any questions, please contact the Office of Environmental Health and Safety at ehs@northeastern.edu or by phone at (617) 373-2769.

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