Unexplained Autoclave Explosion
One morning there was a sudden blast which had laboratory personnel headed for the door. Before too long it was determined that an autoclave had ruptured with incredibly violent force. The room was trashed, broken water connections were streaming and electrical panels were severely damaged. Racks of test tubes, stacks of culture media and trays of used needles awaiting sterilization prior to disposal were splattered across the room by the tremendous concussion. Metal shrapnel penetrated the walls. (Photo) A few minutes sooner or later and those projectiles could have easily struck a lab worker. Luckily, the room was unoccupied at the critical moment.
EHS shut off electrical power, stopped the water flow and quickly surveyed the seriousness of the situation. Next, they verified through visual smoke testing that hazardous biological materials had not blown into the corridors, contaminated building occupants, or escaped to the outside environment. Two things seemed to have prevented this outcome. First, when the 80 lb sterilizer door blew off its hinges and slammed against the wall, it hit the back of well anchored electrical panels which kept it from sailing right through to the corridor. If that was luck, the second advantage was the result of specific design. The autoclave room was independently exhausted, which prevented airborne materials from spreading throughout the building ventilation system. Another concern was the collection of debris, biological waste materials and flood water which covered the floor.
EHS and lab personnel helped estimate possible risks presented by the inventory of likely pathogens. Worst fears were gradually replaced by the carefully considered judgments of some of the country's most knowledgeable professionals.
Although relieved to confirm that human and environmental contamination was prevented by local circumstances, the mess was still extremely hazardous and needed to be cleared as quickly as possible. A clean-up vendor was on the scene before the end of the day. By dawn, eleven drums of contaminated debris were collected from the room - even the contaminated drywall was removed. The only things remaining were three autoclaves and the faint smell of biocide residues.
What caused this catastrophic mechanical failure? Could it happen again elsewhere on campus? Steris was notified and their technicians began inspecting all other steam sterilizers at the facility. All the other units in need of repair and maintenance were identified, but it wasn't possible to determine why the door blew off the ruptured autoclave. An incident of this magnitude calls for serious evaluation. All steam sterilizers at are being identified and evaluated. Each unit will be registered with the State and periodic inspections and maintenance will be conducted. This event, as it turned out, rocked the institution in a generally positive way.
Post-doc Scalded when using Tower-Style Autoclave
A postdoc, Dr. X, was scalded by water while removing items from the top autoclave of a tower-style autoclave. The autoclave was determined to be working properly at the time of the incident.
To autoclave her own materials, Dr. X began to remove a load that belonged to another laboratory while standing on a step-stool. The load in the autoclave consisted of a nalgene tub that contained liter bottles of media with water around them. The water in the tub was near boiling temperature as Dr. X attempted to remove it, and the contents spilled down the trunk and thighs of Dr. X. Another employee had gone to retrieve a cart so that the materials could be removed more safely.
Findings: Factors Contributing to the Accident
- Style/Model of the Autoclave: The tower style autoclave is more dangerous than a standard autoclave. Removing a load from the top autoclave requires standing on a step-stool or platform ladder and stepping down to place the load on a cart. For a short-statured person, a standard step stool is not high enough to allow them to remove a load without reaching over their head. (Note: A standard step stool was used in this incident.) In addition, the bottom autoclave is too low for a tall person to comfortably insert or remove loads.
The facility has appropriate platform ladders in place to allow individuals of different heights to reach the top autoclave. They are bulky, however, and personnel are probably more likely to use a step stool. Facility had not required that liquid loads be autoclaved in the bottom unit before the accident because of ergonomic considerations for tall people. However, since the accident, liquid loads are permitted only on the bottom.
- Training Issues: Despite having attended a recent training session where the participants were brought to the autoclave room and given detailed safety instructions, Dr. X failed to:
a) remove glassware one by one before removing tubs from the top autoclave
b) wear a lab coat (but was wearing autoclave gloves)
c) wait 10 minutes from the time the door is cracked open to allow time for sufficient cooling
d) have cart available.
The other user of the autoclave failed to add no more than 1" of water ( to prevent breakage of glass vessels.)
- The autoclave log had not been filled in by the previous user: Dr. X was removing a load of whose contents she was unfamiliar with. If the log had been completed, she could have asked the owner to remove his/her load.
- Nalgene tubs were used instead of metal tubs: Dr. X indicated that the nalgene tub had buckled. The Nalgene tubs may get less sturdy as they age and may soften when exposed to intense heat.
Lab personnel may prefer using 5" nalgene tubs because they are deeper than the metal tubs and more likely to catch boilover from flasks. However, according to Steris, the nalgene tubs should not be used. The steam compresses the air in the tray, creating an insulation pocket, which interferes with sterilization. Furthermore, the use of the nalgene trays creates a need to use water in the tubs to fill the insulation pocket.
- Adding Water to the Tub: According to Steris, only 50% of autoclave users add water to their autoclave tubs. As mentioned in 4 (above) this water may not be necessary if metal tubs are used. It is believed that adding water to the tub prevents glassware from breaking during sterilization. According to Steris, breakage should not be a problem if sturdy glassware is being used.
- First Aid: Apparently, Dr. X’s burns were worse in areas that were covered by underwear which was not removed. Removal of all clothes covering affected skin should be stressed and tyvex labcoats should be readily available for emergencies.
Additional Recommended Follow-up
a. The Health and Safety Office is exploring the possible use of a hydraulic cart that could be used to take tubs out of the autoclave without the need to bend down or climb a platform ladder.
b. The Health and Safety Office will work with the lab to evaluate if autoclaving loads without water causes glass breakage.
c. Aprons,should be easily accessible in autoclave rooms. Signs should be posted about what personal protective equipment must be worn.
d. The Health and Safety Office will inform lab personnel of the incident and how it could have been prevented through training sessions, signage and a newsletter article. The Health and Safety Office will increase emphasis on autoclave safety in initial and refresher laboratory safety training sessions.
e. The Health and Safety Office strongly recommends that tower- style autoclaves not be installed in any future buildings or renovations.
Two Steam Releases in Autoclave Room Due to Lack of Backflow Preventer, Shorting of Safety Switch, and Configuration of Steam Generators
EHS was notified of two steam release incidents from an autoclave room after the second release. There are two sets of tower style autoclaves in the rooms. There are also 2 steam generators, also situated one on top of the other.
The first release was due to boiling water/steam from the top steam generator which had back-flowed into the piping which connects the DI water generator and the steam-generator. The 3/4 inch PVC pipe melted, causing steam/boiling water to leak out. Immediately afterwards Engineering installed a backflow preventer and replaced the melted pipe with a stainless steel pipe.
A week later there was a steam release from the mechanical over-pressure safety valve of the lower steam generator. Steam was released horizontally at a height of 3.5 feet. It was determined that an over pressure condition in the lower steam generator caused this release. The over pressure should have been avoided by the automatic activation of an electrical safety pressure switch which controls the amount of pressure in the steam generator’s chamber. However, the electrical switch had gotten wet during the previous week’s steam release and this had shorted it out.
Findings and Recommendations
1. Steam release/ electrical hazards from stacking of the generators
There are significant safety hazards caused by having one generator stacked on top of the other. These are being immediately separated.
- Water from the top unit, can drip right onto the high voltage electrical panel of the bottom unit causing an electrical hazard.
- Water dripping from the top unit can drip onto the bottom unit’s safety switchs and valves causing them to fail. As seen in this incident, this can lead to an over pressure condition.
2. Steam is directed at an unsafe location. Possibility of steam filling the room in the event of a release from the safety relief valve
When steam was released from the pressure relief valve during the second incident, the valve directed the steam to shoot out at a 3.5 foot height which could burn or people in the room during a release. There is also a possible asphyxiation hazard. The autoclave technician recommends that the pressure relief valve should be connected directly to a drain to prevent this possibility.
3. Electrical Hazards from accessible high voltage controls
The panel which covers high voltage electronics on each steam generator is currently unlocked on the generators. These must be securely closed and locked.
4. Servicing Area Partitioning the front and back of the autoclaves
There is currently no room behind the autoclaves and generators to allow access to service the units. Following the steam release from the safety relief valve, the only way that Engineering had to access the back of the autoclaves was to make holes in the wall between the autoclave room and the adjoining conference room. .
The room is going to be expanded to allow for a partition wall and a servicing area behind the autoclave. To minimize the chance of injury from steam, the steam generators are being unstacked and relocated behind this partition.
5. Back-flow Check Valve
Engineering has recently installed a stainless steel check valve to prevent backflow of boiling water/steam into the utility line which leads from the DI water. Engineering is checking to ensure that there is a valve for the bottom generator and will install one if necessary.
6. Overcrowding in the Room
The autoclave area is very cramped making it infeasible to use carts effectively. There is no room to pass by if a person is working at the autoclaves or if the autoclave door is open or if someone is working at the drying oven. This condition increases the risks of burns. This situation will be alleviated by the expansion of the room.
7. Emergency Steam Shut Off
There are currently two switches labeled "safety switch" located on the wall opposite the autoclaves. No one knows what is the purpose of these switches or what they control. This information should be obtained. If the steam generators will remain in the autoclave room there must be an emergency switch in the room which can be activated at the far end of the room to shut off the steam source to allow personnel to exit the room in the event of an emergency. Alternatively, an emergency exit should be provided out of the far end of the room.
Lab personnel will receive appropriate training in safety and ergonomic measures when autoclaving.