Nitric acid is a highly-corrosive mineral acid and strong oxidizer used primarily for nitration of organic molecules. Nitric acid reacts violently with alcohols, alkalis, reducing agents, combustible materials, organic materials, metals, acids, cyanides, terpenes, charcoal, and acetone. Not only does it produce exothermic reactions but also toxic, corrosive, and flammable vapors. The violent, reactive nature of nitric acid has led to major incidents at research universities such as Tufts, Texas Tech, and, recently, here at the University of Washington.
On May 9, 2016, a graduate student, working alone in a lab, stored a solution of 70% nitric acid wash in the fume hood as waste. She then tried to dissolve acetates using ethanol, hydrochloric acid, and water for an experiment. Unable to get the acetates to completely dissolve, she decided to discard the solution by pouring it into the nitric acid wash container in the fume hood. Ethanol solutions should be poured into organic waste and hydrochloric acid should be poured into inorganic acid waste.
The graduate student's actions inadvertently resulted in an explosion in the fume hood, which caused the shattering of the glass containing the nitric acid wash, as well as damage to other containers.
In this incident, a visible white gas formed on one of the cracked containers. The reaction of the nitric acid vapors with the contents of other containers would have been controlled by the ventilation system of the fume hood. Unfortunately, the fuming container was removed and set on the floor. Gas and odors prompted people to evacuate, pull the fire alarm, and call 911.
Nitric acid can be extremely hazardous in cases of inhalation (lung corrosive),
skin contact (corrosive, irritant, permeator), eye contact (corrosive), or ingestion.
Luckily, no injuries were reported from this incident. However, it did result in evacuation of the entire building, road closure, and vehicle inaccessibility to other buildings, as well as a response from over 50 emergency personnel and local news crews. Proper handling, storage, and disposal of nitric acid are key to avoiding such incidents (or worse) in the future!
Nitric Acid Safe Use Guidelines
- Use in ventilated areas and in proximity to eyewash and safety shower stations, wearing compatible gloves, goggles, and a lab coat.
- Avoid contact with metals! Nitric acid is extremely corrosive in the presence of aluminum, copper, and oxides and attacks all base metals.
- Store in glass containers that are secured, dry, cool (<23'C/73.4'F), away from sources of ignition, combustible materials, other acids, bases, cyanides, and acetone.
- Storage containers must be dry, as nitric acid can react with water or steam to produce heat, and toxic, corrosive, and flammable vapors.
- Pre-labeled and dated safety-coated glass bottles (PTFE) may be used for nitric acid waste; avoid empty organic solvent bottles.
- Proper waste segregation can help avoid laboratory accidents and explosions. Nitric acid should be added to the oxidizing acid waste stream. In the case of a spill, absorb nitric acid with an inert dry material (earth, sand, or other non-combustible material), place in an appropriate waste container, and neutralize with dilute sodium carbonate.
- Principal investigators planning to use nitric acid should develop a standard operating procedure and provide documented training to all of their respective personnel.
- Principal investigators and/or lab managers are responsible for ensuring all laboratory personnel understand and adhere to safety requirements in the laboratory.
- Following EH&S safety protocols in the Laboratory Safety Manual will help research universities and facilities avoid the health and economic costs of nitric acid accidents.
In the case of a spill, absorb nitric acid with an inert dry material (earth, sand, or other non-combustible materials). Then place in an appropriate waste container and neutralize with dilute sodium carbonate. Labs planning to use nitric acid should develop a safety plan and provide training to their respective lab groups. Following EH&S safety protocols will help research universities and facilities avoid the health and economic costs of nitric acid accidents.