Lab Safety Gas Cylinder Incidents

Arsine Gas Release 

Key Instruction Points:

  1. Read the Label
  2. Use Engineering Controls to Protect Against Unforeseen Hazards
  3. Use Appropriate PPE as required
The Incident - An industrial research lab used arsine gas in a semiconductor- related research project. It had been decided (appropriately in the joint decision of the researcher and health and safety personnel) to use 100% arsine at 200 psig cylinder pressure rather than a 10% arsine / hydrogen mixture which had a cylinder pressure of over 2000 psig. The gas cabinet was equipped with normally-closed pneumatic shutoff valves, a flow restrictor in the cylinder valve, and in-cabinet continuous monitoring for arsine, in addition to other engineering controls. The side of the gas cylinder received from the gas supplier was stenciled with the word "arsine." The regulator had been chosen for 100% arsine gas. When the cylinder was connected to the regulator assembly (with personnel using SCBA) and turned on, the guage needle immediately pegged itself offscale on the regulator. The bourdon guage in the regulator burst and the researcher headed for the door. In moving to the door he heard the sound of the pneumatic valve closing. The gas detection system had immediately signaled for automatic shutdown of the pneumatic valve. No arsine was detected in the lab area outside of the gas cabinet and in-cabinet readings quickly dropped to zero. Subsequent examination of the cylinder contents tag (attached to the cylinder neck) indicated the researcher had actually received a 10% arsine mixture in hydrogen, at the elevated cylinder pressure of 2200 psig. The researcher had not doubled checked the manufacturers identification tag and had relied on the cylinder stenciling, which should not be considered reliable. Fortunately, the engineering controls and personal protective equipment handled the situation effectively
 
Corrective Action - Research staff was informed to check the manufacturer’s tag against their order information and not to rely on cylinder stencils. They were also reminded to utilize engineering controls and protective equipment to minimize the impact of highly hazardous materials incidents when the unexpected occurs.
 

Ruptured Gas Cylinder Destroys Laboratory Hood 

Key Learning Points:

  1. Do not refill gas cylinders with highly reactive or corrosive compounds, including the original compound.
  2. imit the amount of highly reactive, toxic, or flammable chemicals to the quantity necessary for planned experiments. 

Incident Description:  A steel lecture bottle located within a hood in a laboratory ruptured with explosive force. The explosion occurred at night and no one was present in the laboratory at the time of the incident. There was, however, significant damage to the lab hood. The gas cylinder contained methyl nitrite (CH3ONO), which had been synthesized and transferred to the cylinder by a postdoctoral researcher who had left the lab approximately 45 minutes prior to the explosion. After the methyl nitrite was transferred to the cylinder it was left at room temperature in the hood. Although methyl nitrite is known to be explosive when heated or exposed to flame, these conditions were not encountered during the synthesis or storage. The cylinder had originally been used to ship iodotrifluoromethane (CF3I) from the gas vendor, and most recently had been used to store nitrosyl chloride (ClNO).


The Damage: The gas cylinder containing the methyl nitrite ruptured violently, blowing the top cylinder cap off at the weld seam, and twisting the body of the steel cylinder. The cylinder was blown through the front sill of the lab hood, while the blast from the explosion shattered the hood sash, blew off the cabinet doors located underneath the hood, and destroyed the back and top of the hood. The force of the explosion even bent a metal support bracket used to secure utility lines located above the hood. Additionally, the blast produced a crack in an adjacent wall just outside of the hood opening.
 
There were very few chemicals located either in the hood or in the cabinet underneath the hood, a fact that surely prevented a fire or significant chemical spill. Although it appears that there was a flash fire associated with the explosion, a sustained fire was probably prevented by the use of a flammable storage cabinet located away from the hood. The only chemical spill was an unknown quantity of ammonium hydroxide from a container that was broken by the blast. There was no free liquid remaining, indicating that the ammonium hydroxide volatilized and was captured by the hood, or surrounding cabinet materials absorbed the liquid.

The Cause: Although the cause of the cylinder rupture is not known for sure, several contributing factors have been considered. The major suspicion is potential reaction between methyl nitrite and reactive residues in the cylinder. Although the cylinder was evacuated prior to introduction of the methyl nitrite, the cylinder had previously stored iodotrifluoromethane and nitrosyl chloride, both of which could have potentially caused internal corrosion of the cylinder. Another possibility is that small leaks in the cryogenic transfer system may have allowed liquid oxygen to be deposited in the cylinder. Mechanical failure of the cylinder simply due to the pressure of the methyl nitrite is not thought to be likely since the maximum expected pressure was calculated and found to be within the range commonly stored in these type of cylinders. The deformed condition of the cylinder remains also seem to indicate a more violent explosion than would be expected from a simple mechanical failure.
 
Lessons Learned and Recommendations: Several lessons learned and recommendations were identified by the Principal Investigator, the Department Safety Committee, and the Safety Office.
The gas cylinder had been refilled with potentially corrosive gases.
Although steps were taken to evacuate the used gas cylinder, and high heat or pressure was not present, apparently the cylinder contained residues and reactive surfaces that initiated the chemical reaction that led to the explosion. Never refill gas cylinders with highly reactive or corrosive compounds, including the original compound contained in the cylinder.
  • The amount of methyl nitrite synthesized was far in excess of that required for the planned experiments.
Only a few grams of the methyl nitrite were required for the planned experiments; however, approximately 100 grams were synthesized. Limit the amount of highly reactive, toxic, or flammable chemicals to the quantity necessary for planned experiments, or that will be used within a few months. Avoid the use of these compounds whenever possible.
  • The procedure used to synthesize the methyl nitrite was modified slightly from the original published procedure.

Calcium chloride was used as a drying agent instead of the sodium sulfate used in the published procedure; however, this is not thought to have contributed to the incident. Probably more importantly, the reaction was run in a closed reaction.
  • Implement good laboratory safety procedures and emergency response preplanning.

Several general laboratory safety items were identified as either being related to the actual incident, or the response to the incident. These items included: posting of high hazard areas ("designated areas"), prior approval or review of laboratory experiments, proper chemical storage and availability of flammable storage cabinets, and emergency response procedures and training. These are all basic laboratory safety issues. Implementation of the good laboratory practices contained in the Chemical Hygiene Plan, Biosafety Manual, Radiation Safety Manual, and other laboratory safety references will reduce risks to laboratory personnel.
 

Carbon Dioxide Release 

Use caution if you cannot remove a cylinder cap by hand.
 
The Health and Safety Office received an urgent phone call, reporting that a 60 pound carbon dioxide gas cylinder was venting inside a laboratory. According to lab personnel, the cylinder cap had not been removed from the time it was delivered by by the campus vendor. When the employees attempted to use the cylinder, they found that they were unable to remove the cap by hand. They tried to loosen the cap by inserting a long screwdriver through the slats of the cap for leverage. In doing so, the main valve was opened and it began to release its contents. Unfortunately, the cap stayed in place. The lab personnel tried again, unsuccessfully, to loosen the cap, then left the area and notified the Health and Safety.
 
What did we learn from this incident?
NEVER insert a tool into a cylinder cap in an attempt to open it. If you can't remove the cap by hand, call the vendor for assistance. If they are unavailable call your health and safety office. While CO2 is not a flammable or highly toxic gas, respiratory acidosis can occur from exposure to high concentrations. Death from asphyxiation could occur if the concentration and duration were sufficient. Regardless of the chemical hazards of a cylinder's contents, the cylinder, or its cap could become a missile under the right conditions. NEVER attempt to close a venting cylinder. Instead, contact the Health and Safety office immediately.
 

Faulty Gas Cylinder Regulator Causes Explosion 

A chemist was seriously injured in a laboratory iwhen opening the valve on a compressed gas cylinder. The regulator exploded and shattered her jawbone causing unconsciousness. The Canadian Ministry of Labour and the Technical Safety and Standards Association (TSSA) investigated the accident and found a fault in the regulator. The regulator was about 10 years old and may have been retrofitted during that time. The following steps should be taken by all laboratory workers to prevent similar accidents:

Installation of Regulator:
  1. Wear appropriate personal protective equipment such as safety glasses or goggles. Make sure the cylinder is tightly secured before removing the valve cap.
  2. Use only the regulator designed for the gas being used. If the regulator is not the correct one, the connector will not fit. Do not force connections.
  3. Visually check the regulator for evidence of damage or contamination and remove any foreign material before attaching the regulator.
  4. If the regulator is dropped, it should be sent to the supplier for servicing.
  5. When attaching the regulator do not use teflon tape. Use a wrench to tighten the connector securely.
  6. Keep the cylinder between you and the regulator when opening the cylinder valve. Do not stand in front or behind the pressure gauges when applying pressure to the regulator.
  7. Open the regulator's pressure adjusting valve counterclockwise until it feels free. Slowly open the cylinder valve (opening the cylinder valve quickly may cause damage to the regulator valve and seals). When the high pressure gauge indicates maximum pressure, open the cylinder valve fully.
  8. Test regulator for leaks. A soapy water solution can be used for argon, nitrogen, hydrogen or air. For other gases consult supplier.
  9. When not in use store the regulator in a clean place and do not place anything directly on top of the regulator.

Maintenance of Regulator:

We recommend that you do an internal check and maintenance on the regulator every six months and that the regulators are sent to the supplier for servicing every 2 years.   Record all tests and maintenance on a Repair Log Form for Regulators.

Visual Inspection:

  • Carefully examine the entire regulator.
  • Check condition of outlet and inlet. 
  • Look for worn threads and damage.
  • Check to see if gauges are damaged.

Check for Pressure "Creep":

  • Put regulator onto an appropriate cylinder with at least 1500 psi.
  • Make sure pressure adjusting valve is completely free by turning it counterclockwise.
  • Slowly open the cylinder valve until it is fully open. 
  • Set low pressure gauge to approximately 20 psi, then close off the downstream pressure. Record set pressure. Check pressure after 30 minutes and record the pressure.
  • If pressure setting has increased, remove regulator from service and send out for evaluation. 

Functional Test of Regulator:

  • Close regulator by turning the pressure-adjusting valve counterclockwise until key is fully released. 
  • Close the cylinder valve and drain the downstream line. 
  • The low pressure gauge will indicate zero. Record low pressure gauge reading. The high pressure gauge will read full pressure. Record initial high pressure. 
  • If the low pressure gauge does not read zero when all pressure is removed, it may be damaged and must be replaced. 
  • Check high pressure gauge reading after at least 30 minutes. Record high-pressure reading. Any pressure drop will indicate leakage.
  • Release pressure in regulator by turning pressure adjusting-key clockwise. After venting, fully release pressure-adjusting key by turning it counterclockwise.