|Credit: KHON (Picture of "before" by Jian Yu, "after" by the Honolulu Fire Department)|
Accidental causes were considered and only one probable cause remained.
The accidental cause of this explosion was caused by the detonation of compressed gasses to include: Hydrogen, Carbon Dioxide, and Oxygen within the air tank. A digital pressure gauge used to check the pressure within the tank was not rated or designed (not Intrinsically Safe) to be in a flammable gaseous atmosphere. When the OFF button was pressed, an electrical arc/spark created within the gauge detonated the flammable gas within the tank causing the explosion.
Level of Certainty: Probable, with a reasonable degree of fire investigative certainty.Please forgive the gruesome details that I am going to share next, but I think they're essential to understanding the incident:
On this particular day, she moved and filled the tank with a set amount of gasses using the Ashcroft 300 psi digital gauge that is battery operated. This gauge is a push button type for ON and OFF. When she disconnected the hoses used to fill the tank, she checked the pressure in the tank to verify the amount to be 117 psi. She then pressed the OFF button and the tank exploded. Prior to the explosion, she did not hear any sounds of escaping or leaking gasses from any of the fittings or pressure relief valve.
She did not lose consciousness or hit her head; she was aware that she lost her arm in the explosion. She couldn’t open the door to the lab, the door was stuck closed. A person by the name of Savannah was there to help get the door open and help her out of the lab.
She added that earlier in the week, she was conducting another experiment using a smaller one gallon size air tank assembly nearly as identical as the one that failed using similar components to include the Ashcroft 100 digital pressure gauge and the premixed gasses. The tank pressure was set to 27 psi. After reading the gauge, she pressed the OFF button and a small internal explosion occurred. She related to me that there was evidence of a soot and smoke stains.
Static shock also appeared to have been a problem as Ms. Ekins-Coward would get shocked on occasion when touching the tank.
She brought this information to the attention of Mr. Yu who she said told her don’t worry about it.What immediately bothers me about this incident is that I have been simplistically trained to think about the "fire triangle": that oxygen, fuel and a heat source are needed for a fire. In this case, because the Yu Laboratory and Dr. Ekins-Coward were running mixtures of hydrogen, oxygen, you have both fuel and oxygen, so most of the preventative measures should have been aimed at reducing the risk of a spark. That there were near-misses is supremely tragic - this didn't have to happen.
(Readers, what do you think here? Is there another root cause I'm missing? Should attention have been paid elsewhere?)
To make this even more interesting, it appears that we have a disagreement as to who designed the system. I think this sort of thing is bound to happen during police investigations; two people will disagree about something key to the event. From the report's interview with Dr. Yu (emphasis mine):
The following was related to me by the named individual above:
The victim Thea Ekins-Coward was working as a Post-Doctoral Fellow trained in Marine Science and a Chemical Engineer.
She was hired by Dr. Yu October 2015 to conduct research in bioplastics and biofuels.
In response to my questions he related that:
The tank that failed was Ms. Ekins-Coward's design. She bought the equipment (tank, digital gauge, pressure relieve valve, and fittings) between November 2015 and January 2016. The tank was to have been rated at 10 bar or 150 psi. When the tank was assembled with its parts, a pressure test was done using the buildings air which produced 91.2 psi. Several leaks were detected. So the tank assembly was taken to the Universities maintenance for help in stopping the leaks.
This particular tank was used to contain a mixture of gases to include: 70% Hydrogen, 10% Carbon dioxide, and 20% Oxygen in that order and to a normal operating pressure of 50 psi.
The tank was not grounded and was normally moved from a stored location to areas where it could be filled. The tank would be moved approximately 3 feet to fill it with Hydrogen and Carbon Dioxide, then moved approximately 13' so it can be filled with Oxygen.And here's the relevant paragraph from the interview with Dr. Ekins-Coward:
The air tank and assembly that failed was purchased between November 2015 and January 2016. The parts were assembled and pressure tested with the building supplied air. This output of air was 91.2 psi which was sufficient enough to cause leaks at the connections so the tank assembly was taken to the Universities maintenance shop where they helped stop the leaks. The design of this tank assembly was that of Dr. Jian Yu. The tank was rated at 145 psi.So, it's time for some questions that will ultimately need to be answered:
- Who designed the tank and selected the pressure gauge?
- Is it accurate that both the PI and postdoc were trained as chemical engineers, as brief Google searching seems to indicate?
- What is the role of the institution and its EH&S office in this? Did the EH&S office know about the Yu Laboratory's experimental systems?
- This was clearly an unsafe experimental setup - will the comments about this experiment being safely performed since 2008 be walked back?
- What disciplinary actions are going to be carried out by the department or institution?
- Will there be civil penalties from the state occupational health and safety regulatory agency or from the local fire authorities?
- Will there be criminal penalties?
UPDATE 160419 4:49 PM: Jyllian has a story up about the Honolulu Fire Department report at C&EN's website; some background on the experiment follows:
The gas mixture was “food” for bacteria being used to produce biofuels and bioplastics. Ekins-Coward was working for the Hawaii Natural Energy Institute under researcher Jian Yu. A 2013 paper by Yu indicates a set-up in which gases are plumbed through a mixing device called a gas proportioner directly into the bioreactor (Int. J. Hydrogen Energy 2013, DOI: 10.1016/j.ijhydene.2013.04.153). The gas gauge identified in the paper is an “intrinsically safe” model designed to prevent ignition.
But after Ekins-Coward started in the lab last fall, she purchased a 49-L steel gas tank, a different gauge not rated as intrinsically safe, a pressure-relief valve, and fittings, and she put them together, Yu and Ekins-Coward told fire department investigators, according to the report. Ekins-Coward would add the gases to the portable tank, which would then be connected to the bioreactor. She was using a mixture of 70% hydrogen, 25% oxygen, and 5% carbon dioxide for her experiments, the report says.
In the week before the incident, a similar set-up with a 3.8-L tank resulted in a “small internal explosion” when Ekins-Coward pressed the off button on the gauge, the fire department report says.Also, she links to a longer version of the report.