Lab Safety Explosions Incidents

Chemistry

  • Lithium AlumTetrahydrofuran explosioninum Hydride/ Tetrahydrofuran explosion
  • Explosive Decomposion of an Organic Azide
  • Stirred Reaction Flask Explosion
  • Chemical Solution Preparation Explosion
  • Phenyl Azide Solution erupts during vacuum distillation
  • Bursting Chemical Container
  • Unintended Overpressurization of Sealed Vial Results in Rupture
  • A Bench Scale Chemical Reaction Results in an Explosion
  • Gas Cylinder Gasket Melted Due To Reaction with Anhydrous Hydrogen Chloride
  • Chemical Container Failure Due to Over-pressurization
  • Texas Tech Laboratory Explosion

 

Incompatible Chemicals

Oxidizer Solvent Explosion 

A corrosive storage cabinet under a chemcial hood in a University undergraduate laboratory was the site of an early morning explosion.   Luckily, no one was standing in front of the hood when the explosion occured.   We believe the explosion resulted from nitric acid (an oxidizer) and an organic solvent being mixed in a closed container.

Niric acid reacts violently with most organics resulting in heat, gas or fire. In a sealed container, the pressure would increase due to the expanding gas.   Never mix nitric acid with organic materials (especially in a sealed container) unless the reaction has been thoroughly investigated.  Do not store nitric acid in the same cabinet as organic solvents or organic acids such as acetic acid.
 
Incidents such as this have occurred on this campus and at other universities in the past, some with more severe consequences.  Help make your campus safer by following proper storage guidelines for chemicals.
 

Glass Waste Bottle Ruptures, Possible Reaction of Incompatible Chemical Wastes 

Key Instruction Points:
  1. Chemical containers should be triple rinsed and dry before being used for waste accumulation.
  2. Wear safety glasses while in the laboratory, even while performing non-laboratory work.
A graduate student sitting at a lab computer was surprised by a chemical waste bottle which burst and sprayed nitric acid and shards of glass all over the lab.
 
Approximately 2L of nitric acid waste had been accumulated in a chemical waste bottle which originally contained methanol. Over the course of 12-16 hours, it is likely that some residual methanol reacted with the nitric acid waste and created enough carbon dioxide to overpressurize the container. Two other waste containers in the hood were severely damaged and several others were cracked or leaking.
 
Fortunately, the laboratory worker was not injured.
 
Chemical containers should be triple rinsed and dry before being used for waste accumulation. Safety glasses should always be worn while in the laboratory, even while performing non-laboratory work.
 

Mixing Diaminopropane and Potassium Hydride 

A Post-Doctoral Fellow was adding 100ml of Diaminopropane to 150g of Potassium Hydride in a 2L, 3-necked, round-bottomed flask while under Nitrogen.  As she was adding the Diaminopropane, the reaction began to foam and fill the flask.  As she was replacing the stoppers, the mixture built pressure and then splashed her right arm, left wrist, face, and neck. 
What can be done to prevent this from occurring again?
Before setting up an experiment, thoroughly investigate the properties of materials involved. If you are unsure, ASK!  Potassium Hydride is an extremely reactive species.  For this particular reaction, 150g of hydride could generate nearly 60L of hydrogen gas at STP! 
Here are some general recommendations:
  1. This was a large scale reaction.  The Post-Doc, who had never done this reaction, should have started out with very small quantities and then scaled-up (by no more than a factor of 5 each time).
  2. Rather than adding the Diaminopropane to the hydride, add the hydride to the amine.  By slowly adding the hydride, you can control the reaction and the subsequent foaming (resulting from the hydrogen gas).  It would also be a good idea to have a cooling bath on a lab jack underneath the flask in order to slow the reaction down...just in case.
  3. When working in the fume hood, keep the sash as far down as possible at all times. If you have to lift the sash to make an adjustment, use a safety shield (as appropriate) and/or use a face shield (in addition to your safety glasses).
 

Two Explosions Involving Aqua Regia 

Key Learning Points
  1. Use a reagent that is milder than aqua regia for cleaning glassware if it will suffice.
  2. Do not take aqua regia out of the fume hood in which it was prepared, and do not store it there either; make only what you need and destroy the residue.  Aqua regia can be destroyed by cautious and careful dilution with water - talk to your supervisor or your safety office for a detailed procedure. If necessary, the solution can then be neutralized and disposed of in the approved manner.
  3. Never put aqua regia in a closed container or near flammables.
There have been explosions involving aqua regia ( a mixture of hydrochloric acid and nitric acid) reported at two universities. Both of the incidents took place in chemistry laboratories.
 
In the first incident, a graduate student was using aqua regia for the cleaning of NMR tubes. When he was finished, he placed the residues (about 50-60 ml) in a 4 litre waste bottle, capped it tightly and placed it in a flammable storage cabinet. Approximately one hour after the bottle was placed in the cabinet, it burst, breaking an adjacent bottle of pyridine. Luckily, the pyridine did not ignite and other nearby bottles containing flammable solvents did not become involved. The pyridine leaked onto the floor, where it dissolved floor tiles and created a lingering bad smell.
 
The second incident occurred in a fume hood in a synthetic chemistry laboratory.   A tightly closed waste bottle containing used aqua regia exploded, most probably due to  pressure buildup inside the bottle.
 
Since the sash was not completely closed the broken waste bottle was not contained. Broken glass as well as some liquid acid waste were thrown out of the hood.  Since nobody was near the hood at that moment, there were no injuries.   Moreover, a nearby bottle of mercury nitrate waste was also broken as well as the secondary container, so that a small spill (less than 1 liter) of liquid acid and solid mercury nitrate occurred inside the hood.
What is aqua regia?
Aqua regia has been used by chemists for centuries, especially as a medium for dissolving noble metals but also for other purposes. It is a mixture of concentrated hydrochloric and nitric acid which forms a powerful oxidizing medium. Mixing an oxidizer with organic materials may result in a highly exothermic reaction.  Even without other materials present, a chemical reaction occurs slowly and brown fumes of NO2 can be observed (in freshman chemistry terms, nitric acid is reduced and hydrochloric acid is oxidized). The activity as a dissolving agent decreases slowly and so, by definition, the solution is unstable - it should be used "freshly prepared".
Rules for using aqua regia
Aqua regia is often used as a substitute for chromic sulfuric acid cleaning solutions.   However, aqua regia is also corrosive and strongly oxidizing.  It  is essential for some purposes but should not be used for routine cleaning of glassware.  If a milder reagent will suffice avoid using aqua regia.  Alternatives include ultrasonic baths, alconox or similar detergents, Pierce RBS-35 (available from VWR) or similar detergents or biodegradable surfactants. 
 
Be aware that sufficient pressure can build up in a  short amount of  time to burst the container,  even from a very small volume of aqua regia.
 
If it is decided that aqua regia is needed, wear protective clothing (goggles, gloves, coat) and work in a clean well-ventilated fume hood. Keep the sash down when reactions are in progress. Never take aqua regia out of the hood.
 
Prepare it, use it, and destroy any excess in the hood in which it was prepared.
 
Only prepare the amount of aqua regia you need for immediate use. Never store it and never put it in a closed vessel, since evolved gases will cause a pressure build-up and possible explosion.
 
Aqua regia is a strong oxidizer. It is incompatible with organic solvents, flammables and any reducing agents.
 

 

Refrigerator/Freezers

Lab Freezer Explodes 

Key Instruction Points:
Flammable liquids must only be stored in refrigerators which have no internal ignition sources.
Incident Description: 
Many small tubes of petroleum ether were stored in an ordinary domestic freezer.  The tubes were not sealed well and over time the petroleum ether evaporated in sufficient quantity that the concentration exceeded the low explosive limit, about 1.0%.  A spark from an internal component caused the freezer to detonate.
Injuries and property damage:
There were no personal injuries as the explosion took place at night.  There was $11,000 damage to the room and $25,000 damage to equipment in 1982 dollars.  This would be well over $250,000 in 2001 dollars.  Along with the freezer, one liquid scintillation was destroyed and another was seriously damaged.
Primary cause of the incident: 
Petroleum ether, a very flammable liquid* was stored in an ordinary domestic freezer which has components  (e.g., thermostat, light switch) which generates sparks.  This apparently caused the vapor of the liquid to detonate. 
 
*With a flash point as low as -56 °F, petroleum ether is classified as a Class 1A flammable with an NFPA 704 fire hazard rating of 4.
Recommended Corrective Action:
All materials with a flashpoint below 100 °F may only be stored in a UL approved flammable materials storage refrigerator or freezer.  These units do not have any internal ignition sources.
 
All ordinary domestic refrigerators and freezers must be labeled with the phrase "No materials with a flashpoint below 100 °F may be stored in this refrigerator/freezer."
 
Lab supervisors must vigorously enforce both of the above items.

 

Semiconductor Experiments

Failure to Manually Purge Hazardous Gases

Key Instruction Points:
  1. Don't rely on procedures - insist on engineering controls.
  2. Use engineering controls to protect against unforeseen hazards.
An experienced physical scientist (Ph.D. 15-20 years) at  an industrial research lab used hydrogen and phosphine gas, along with other materials, in a metal organic chemical vapor deposition system. This was a slightly modified commercial system that operated at atmospheric pressure. The reactor was contained in a secondary enclosure with exhaust ventilation and toxic and flammable gas detection equipment linked to automatic gas shutoff valves. The equipment operating procedure involved a manual inert gas purge prior to flow of hazardous gases. When considering a modification of the system to make the purge process automatic, the manual procedure was thought to be acceptable since the only one who operated the system was the physicist who bought and built the equipment and his coworker who was also experienced and trained. The addition of the automated purge feature was considered an unnecessary hardship. Three months after startup an overpressurization of the reactor occurred, cracking the glassware and leaking the gas into the secondary containment. The gas monitor detected the leak and caused automatic shutdown of gas flow. No gas escaped secondary containment. The physicist indicated that he had forgotten the purge step of the process.
Corrective Action:
The physicist modified the equipment to include an automatic inert gas purge. This involved very little time and expense. This incident is consistent with other mishaps in which highly intelligent, experienced, and well trained personnel miss a critical step in the process. The need for engineering controls for high hazard processes was emphasized in employee training and hazard reviews.