Chemical Waste Bottle Exploded in Lab

 

 

What Happened?

An over-pressurized chemical waste bottle exploded in a lab. The explosion was heard across the floor and the floor below, but fortunately no one was around when the explosion occurred. Several people entered the lab to inspect the area and found shards of broken glass and corrosive liquid scattered around the lab. An acrid smell filled the hall near the site of explosion. A broken bottle cap was found several feet from the site of explosion. The lab members evacuated the lab and reported the incident to the EH&S on-call specialist. The Fire department and the hazardous waste group were also contacted. Due to the extent and unknown nature of the chemical contamination, the clean-up was carried out by an outside contractor. A hazardous waste label was recovered at the scene which described the contents of the bottle as 50% nitric acid, 25% sulfuric acid, and 25% hydrochloric acid, similar to aqua regia. 

What Was The Cause?

Aqua regia (3 parts of concentrated hydrochloric acid and 1 part of concentrated nitric acid) and similar strong acids are used for removing trace amounts of organic compounds and metals from glassware. After use, it is often wrongly stored in closed containers and sometimes even re-used.

Aqua regia decomposes over time generating toxic nitrosyl chloride, chlorine gas and nitrogen dioxide. If sulfuric acid is present, toxic sulfur dioxide is also released. 

In addition to being a strong acid like hydrochloric and sulfuric acids, nitric acid is also a potent oxidant. Thus, contamination of nitric acid solutions with organic compounds, which act as reducing agents, can cause a violent exothermic reaction.

 

The solution could have been contaminated with organic material. Possible sources include:

  • The waste container was not properly cleaned before adding aqua regia 
  • Aqua regia was heavily contaminated with organic materials during cleaning activities 
  • Organic waste was improperly added to the waste container

What Corrective Actions Were Taken? 

  • Training on correct preparation, handling, and waste disposal of aqua regia and similar solutions 
  • Review and updating of SOPs and PPE requirements
  • Implementation of vented caps for pressure-generating chemical waste 

How Can Incidents Like This Be Prevented?

  • All work with aqua regia or similar solutions must be performed inside the chemical fume hood using clean glassware and wearing appropriate PPE 
  • Dispose of aqua regia and other nitric acid solutions into clean waste containers with vented caps 
  • Avoid mixing organic waste with aqua regia or other nitric acid solutions
  • Do not store aqua regia solutions  
  • If possible, substitute aqua regia cleaning solutions with safer alternatives including ultrasonic baths, alconox or similar detergents, Pierce RBS-35 (available from VWR) or similar detergents or biodegradable surfactants

 Resources

Aqua regia

Two explosions involving aqua regia

Vented cap video

Examples of different styles of vented caps:  https://www.calpaclab.com/vented-caps/

 

 

 

 

 

 

 

QUICK ACTION TIPS 

1. If cross contamination of aqua regia with organic compounds is suspected, close the fume hood sash, alert others in the area and report situation to your supervisor and your safety office

2. In case of skin contact, immediately flush skin with water for at least 15 min. Seek medical attention if significant exposure

3. In case of eye contact, immediately flush eye(s) with copious amounts of water for at least 15 min. Seek medical attention immediately

  

Hazards of Aqua Regia

• Strong oxidant

• Highly energetic and potentially explosive reactions in the presence of reductants such as organic compounds or metals 

• Highly corrosive

• Releases toxic gases