OAKLAND COUNTY, Mich. – A former Oxford Center employee testified that grounding wrist straps that prevent static electric buildup in hyperbaric chambers stopped being used in 2017, years before a 2025 explosion that killed a 5-year-old boy.
Tamela Peterson, 59, of Brighton, Jeffrey Mosteller, 65, of Clinton Township, Gary Marken, 66, of Spring Arbor and Aleta Moffitt, 61, of Rochester Hills, were charged after Thomas Cooper was killed when the hyperbaric chamber he was receiving treatment in exploded at the Oxford Center in Troy on Jan. 31, 2025. The boy’s mother was also injured in the explosion.
Recommended Videos
The four workers are accused of ignoring several safety guidelines for operating hyperbaric chambers, including not using a grounding wrist strap, rolling back the chamber cycle count, giving the 5-year-old boy a blanket straight from a running dryer, using polyester pillows and more.
They appeared in court before Oakland County Judge Maureen McGinnis in 52-4 District Court on Monday, Jan. 12, 2026, for a continuation of their preliminary examination. The purpose of this hearing is for the judge to decide whether a crime was committed by each defendant and whether enough evidence exists to refer the case to a higher court for trial.
Bowen Geng, a former employee who worked at the Oxford Center for nearly 10 years, testified about employee training, safety protocols, and patient procedures during his time at the facility, offering insight into how policies were communicated and implemented. Mosteller’s attorney, Alona Sharon, called him as a witness. He testified under an immunity agreement.
He worked at the Oxford Center in Troy from 2015 to 2025, so he was employed by the company when Cooper was killed in the explosion. However, Geng was not present at the center on the day the explosion happened.
Geng’s testimony comes after another former employee testified about how his safety concerns were dismissed while he worked at the Oxford Center in Brighton.
Read more --> ‘Deal with it’: Former Oxford Center employee testifies about how safety concerns were dismissed
Grounding wrist straps were previously used, but not for the majority of his time there, ex-employee says
Geng was questioned about policies related to patient wrist grounding straps. He testified that when he first began working at the Oxford Center, wrist straps were in use. Later, he was told they were no longer necessary.
“I would say the grand majority of the time I was there they were not used,” Geng said.
Geng testified that when he first saw that the grounding wrist straps weren’t being used, he was “a little shocked,” but was assured they weren’t needed.
When asked who had the authority to make that decision, Geng said, “Tammy.”
Geng said Mosteller started working at the Oxford Center in 2019.
The center stopped using grounding wrist straps before Mosteller was hired.
Geng recalled that when Mosteller was hired, Mosteller was unsure about the center’s policy of not using grounding straps.
He said he wouldn’t say Mosteller was concerned, but that he wanted to do some testing on grounding without using a grounding strap.
Related --> Key safety item found in ‘junk drawer’ after Troy hyperbaric chamber death, officer testifies
Sechrist, the manufacturer of the hyperbaric chambers, and the National Fire Protection Association (NFPA) code for fire safety, say that grounding wrist straps must be used in monoplace hyperbaric chambers.
He also testified that he completed a safety director course taught by Jeff, which was part of the Oxford Center’s training program. The course was offered to both staff and outside participants.
Geng said that he participated in one of the first pilot courses in 2019 or 2020 and that the course was still being offered as recently as 2025.
When asked whether hyperbaric technicians were required to take the course, Geng said the initial group was required to complete it.
He also testified that Moffitt did not take the safety course. Moffitt was the technician who was operating the chamber when Cooper was receiving treatment and it exploded.
‘One of the best’: Former employee says Moffit was good at her job as a hyperbaric tech
Geng said that he worked directly with Moffitt during her time at the Oxford Center. He said he helped train her and worked alongside her.
He indicated that new staff, including Moffitt, learned procedures by shadowing technicians and then by working shifts and being shadowed by the experienced technicians.
When the former employee was asked about how Moffitt performed in the job, he confirmed that she was good at her job and said she was “one of the best” technicians.
Geng said Moffitt said her patient care was good and she wasn’t afraid to ask questions. He also testified that Moffitt took really good notes.
He said that technicians were trained to make all required chart entries at the beginning of a dive.
According to Geng, he would occasionally “pre-chart” and fill in expected times in advance, particularly when the center was busy, as a matter of efficiency. He said he tried to avoid pre-charting when possible but acknowledged it was sometimes used during high-volume periods.
Geng said that if something changed during a session, such as a patient needing to use the bathroom, he would add a note in the log that explained what happened.
He said Moffitt took good notes and would make sure information was documented in the paper log book and the electronic records.
Regarding corrections, Geng testified that there was no strict deadline for updating or correcting entries, but staff were expected to make changes as soon as possible. He said corrections should be completed before the end of a technician’s shift.
Safety checks, chamber preparation
He testified that he conducted verbal safety checks with every patient before treatment, regardless of how many prior sessions they had completed. Even if a patient was on their 30th dive, the verbal check was still performed.
For child patients, Geng stated that staff would direct questions to the parent.
Geng testified that as a technician, he was responsible for laundry and for preparing patient comfort items for hyperbaric chamber sessions. This included providing blankets and pillows.
Typically, patients received two pillows, a bottle of water, and a blanket. Patients were given a choice between a warm or cold blanket, with warm blankets prepared by placing them in a dryer.
Marken’s role at the facility
Geng testified that Marken was known to him as a facilities or maintenance manager and was contacted for building-related issues such as plumbing problems, drafts from doors, or safety equipment like smoke detectors and fire extinguishers, but not for hyperbaric operations or technician training.
He said Marken wasn’t in charge of training hyperbaric technicians, advising on wrist straps, or overseeing chamber use, and Geng would not have relied on him for patient safety or treatment concerns when it comes to hyperbaric chambers.
Geng recalled limited contact with Marken at the Troy facility, stating that after 2022, he did not remember seeing him there and that their interactions were primarily related to maintenance matters.
Prosecution asks about decision-making, grounding straps, training
Assistant Attorney General Chris Kessel asked about decision-making at the Oxford Center, and Geng testified that if there was anything important that needed to be decided, Peterson made the decision.
He confirmed that she was also responsible for ordering items that the center needed, including office supplies, sheets and pillows.
He confirmed that when he first started working at the center, grounding wrist straps were used to mitigate the risk of static electricity and fire in the hyperbaric chambers, but that practice stopped around 2017 at Peterson’s direction, before safety director Jeff Mosteller was hired.
Geng said he was surprised when the straps were discontinued and confirmed that he trained Aleta Moffitt in the same manner he had been trained.
Geng confirmed that grounding was supposed to be checked, but he did not perform it himself before Mosteller was hired as safety director. He said one of the other technicians may have been checking the grounding at that time, but he wasn’t sure.
He said the testing he did with Mosteller to check the grounding on the chamber, to see if grounding straps were necessary, was only conducted once, and was never peer-reviewed or published anywhere, to his knowledge.
The chamber that exploded had exceeded 20,000 cycles, the maximum recommended before replacement, according to Sechrist, the manufacturer. Geng said he was aware that Sechrist employees had told Peterson the chamber reached over 20,000 cycles in 2022, but he never placed patients in chambers that had exceeded 20,000 dives, and that the Oxford Center’s culture had stressed safety.
Previous coverage about cycle counts --> Oakland County hyperbaric chamber explosion: What we learned from experts, police during key hearing
Although the staff believed the chambers were fully grounded through contact with grounded surfaces, Geng acknowledged that not wearing straps created a risk of fire.
Geng said he was friends with both Mosteller and Peterson and her family, and said he cared for them.
When asked whether he would ever place a patient in a chamber without a grounding strap if he believed it would put their life at risk, Geng responded, “No, I would not.”
What’s next
Testimony has concluded in the preliminary hearing.
They will return to court on Tuesday, Jan. 20, 2026, where the prosecutor will make arguments to the judge explaining why the case should be bound over to a higher court, followed by the defense attorneys’ arguments.
After that, the judge will consider all the evidence that was presented and determine if there is probable cause to bind the case over.