OAKLAND COUNTY, Mich. – The four people charged in the death of a 5-year-old boy who was killed in a hyperbaric chamber explosion at a health care facility in Oakland County were back in court this week.
Tamela Peterson, 58, of Brighton, Jeffrey Mosteller, 65, of Clinton Township, Gary Marken, 66, of Spring Arbor and Aleta Moffitt, 60, 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.
All four workers appeared in 52-4 District Court before Judge Maureen McGinnis on Monday, Dec. 1, 2025, and Tuesday, Dec. 2, 2025, for a continuation of their preliminary examinations.
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.
The first two days of their preliminary hearings were held in September, and two more days were held on Dec. 1 and Dec. 2. The hearing is scheduled to continue on Dec. 12.
Read more from the September days of the hearing --> Testimony says 5-year-old’s hyperbaric chamber death at Oxford Center was preventable
Monday, Dec. 1, 2025
The first person called to testify on Monday was Andrew Melnyczenko, the technical and safety director of the hyperbaric and altitude medicine program at the Mayo Clinic in Minnesota. He has nearly 30 years of experience in hyperbaric medicine and chairs the Hyperbaric Oxygen Safety Committee for Undersea and Hyperbaric Medical Society.
Melnyczenko has also taught safety courses for medical professionals and served in the U.S. Air Force as an aerospace physiology technician.
When Melnyczenko was called to testify in September, the defense argued that Melnyczenko didn’t have qualifications related to fire prevention and that there was little he could say that they hadn’t already heard from Burman.
The prosecution argued that there can be more than one expert in any given field and that Melnyczenko would primarily focus on what parts of the hyperbaric chamber’s manual were allegedly ignored by workers at the Oxford Center. The judge allowed Melnyczenko to be called to testify.
On Monday, Dec. 1, Melnyczenko was asked about safety guidelines for operating hyperbaric chambers.
The concentration of oxygen that pressurizes multiplace chambers (Class A) is 21%, while the concentration of oxygen in monoplace chambers (Class B) is generally around 100%. According to Melnyczenko, there is an increased fire risk with monoplace chambers because of the increased oxygen.
“Increased oxygen concentrations cause a spark or flame to burn intensely, so it increases the flame spread rate by more than five times and the heat of a fire by more than 1,000 times,” said Melnyczenko.
Grounding straps
Due to this increased fire risk, grounding straps are required and are a “critical safety component” for monoplace chambers, because they keep static from building up and discharging.
He was also asked if he knew of any instance of a child choking on a grounding strap, and Melnyczenko said he had never heard of this happening.
Melnyczenko explained that at the Mayo Clinic, staff always confirm a patient’s identity and complete all safety checks, including using a grounding strap, before treatment in a hyperbaric chamber—regardless of whether they recognize the patient.
He also testified that he worked with Mosteller at Beaumont from 2004 to 2005, and during that time, Mosteller was his supervisor. Melnyczenko said they lost contact about seven years ago.
Melnyczenko was asked if they used grounding straps when he worked with Mosteller, and he said that at the time they were working on Class A chambers, so the use of grounding straps didn’t apply.
Polyester pillows
Melnyczenko said that after the hyperbaric chamber explosion, he and Burman, who previously testified, went to the Oxford Center with law enforcement officials.
He said the pillow in the exploded chamber was destroyed, but the other pillows at the center appeared to be of the same type, with a 100% polyester filling.
This is problematic because polyester is capable of generating more static than other materials, and may have contributed to the static generation in the chamber that exploded, according to Melnyczenko.
Melnyczenko also reviewed Thomas’ medical records, including the consent form for treatment. He said the form didn’t mention the risk of fire at all, and wasn’t signed by any staff member.
Review of video footage from day of explosion
Melnyczenko also testified about reviewing video footage of the explosion.
Inside the hyperbaric chamber with Thomas were a mattress covered with a sheet, a pillow, and an extra blanket. Melnyczenko said Thomas was wearing pajamas, and the 5-year-old wasn’t wearing a grounding strap.
Melnyczenko said about 40 minutes after the chamber was pressurized, a flame had sparked.
Thomas was moving from left to right and up and down inside the chamber, and that movement exposed a portion of the mattress.
His left knee moved toward the mattress, and that’s where the flame was seen, according to Melnyczenko.
Melnyczenko explained that because Thomas wasn’t wearing a grounding strap, the only thing that could’ve grounded him was the grounded mattress.
“So if he had built up static and came into contact with a grounded surface, then that increases the potential for a static discharge to occur,” Melnyczenko said.
Menyczenko said because “the grounded mattress was exposed, and there was a potentially high-energy charge surrounding Thomas,” the discharge happened.
User manuals
Melnyczenko said manuals for operating hyperbaric chambers are upgraded as National Fire Protection Association (NFPA) fire codes are updated to improve safety. They’re also updated if there are new features are added to chambers.
When Melnyczenko wrote his report about the incident, he referenced a slightly newer manual than the one that was found at the Oxford Center after the explosion, but said the safety requirements were the same, and the differences involved where in the book information was placed.
However, Melnyczenko said using a grounding strap for these types of hyperbaric chambers is a requirement that’s in all manuals.
During cross-examination, Melnyczenko said he didn’t believe the explosion was mechanical and explained that everyone working on hyperbaric chambers at his facility ensures patients are grounded.
In addition, Marken and Peterson’s defense attorneys questioned Melnyczenko about a conversation he had with Burman after Burman gave his testimony in September.
Melnyczenko said they didn’t discuss what questions Burman was asked when he testified, and only talked about Burman’s personal experience on the witness stand.
When asked if he knew what questions Burman had been asked, Melnyczenko said he only did once it was made public by the media, and not from talking with Burman.
Alona Sharon, Mosteller’s attorney, said Melnyczenko’s sequestration order was violated and asked for his testimony to be thrown out.
She claimed that allowing his testimony would violate the court’s orders and gave Melnyczenko an “unfair advantage” because it allowed him to prepare answers for the questions that he may be asked.
McGinnis said he clearly answered that they only discussed the experience of testifying, with no attempt to learn the questions. The judge also noted the case’s public record due to media coverage.
McGinnis decided that Melnyczenko’s testimony would be included.
Ellen Michaels, Moffit’s attorney, questioned Melnyczenko about differences between his report and Burman’s, specifically regarding the source of static electricity. Melnyczenko stood by his conclusion that static discharged from the pillowcase to the grounded mattress, explaining that the polyester pillowcase material generated high static concentrations.
He described how Thomas was sitting on the pillow, which came in contact with his skin, allowing static to accumulate around his body and discharge to the ground. Melnyczenko noted that Thomas was moving during treatment, which would have increased static buildup on the pillow.
When Michaels challenged whether Thomas was sitting on the pillow at the time of the spark, Melnyczenko maintained that he was.
Melnyczenko said a grounding bracelet worn by the patient would have provided a grounded pathway to absorb the static energy.
He also testified that no Sechrist employees were present during his initial investigation in February.
Regarding safety protocols at the Oxford Center, Melnyczenko said he did not observe a safety pause in the video showing the start of treatment on the day Thomas died.
He explained that a safety pause must occur at the chamber side to check grounding straps and that the safety check must be documented. Melnyczenko said he saw no documentation of a safety pause at Troy.
He described how safety protocols are typically created by a safety director and medical director, not by the chamber operator. Melnyczenko noted that grounding the patient was not included in the daily, weekly, or monthly checklists he reviewed.
Without checking the grounding bracelet, he said any safety pause would be incomplete for a Class B chamber, according to industry protocols.
When asked about licensing requirements for chamber operators, Melnyczenko said Michigan does not require licensing. Training typically occurs on the job.
Melnyczenko continued testifying on Tuesday, Dec. 2, 2025.
Sechrist Industries VP called to testify
The next person called to testify on Monday was Majid Mashayekh, the vice president of quality assurance for Sechrist Industries.
Mashayekh explained that Sechrist field service engineers follow specific guidelines when they go to do maintenance on chambers, including running a full cycle to verify chamber functionality.
He also talked about how user manuals are included with every chamber that gets delivered, and that grounding wrist straps are required for treatment inside a chamber.
The witness testimony also included a discussion about cycle counts.
Mashayekh explained that chambers have a visible cycle counter and a logbook for recording usage, and when field engineers check chambers, they take note of the cycle count.
The defense attorneys questioned the accuracy of the cycle counter and also inquired about the company’s procedures to ensure that a field engineer doesn’t record the incorrect count number.
In November 2022, Sechrist informed the Oxford Center that the chamber where the explosion happened had exceeded 20,000 cycles and would no longer be serviced.
While the chamber had reached its usage limit, Mashayekh testified that the explosion didn’t have anything to do with the cycle count.
Tuesday, Dec. 2, 2025
On Tuesday, December 2, 2025, Melnyczenko was the first person called to testify, allowing the defense attorneys to continue their cross-examination.
Melnyczenko has experience treating pediatric patients in hyperbaric chambers, mainly at the Mayo Clinic and a few at Beaumont. He said these cases involved patients who needed wound healing care, and he has never treated pediatric patients for autism or ADHD.
He noted that the chamber is grounded, and since the mattress is touching it, it is also grounded.
Melnyczenko explained that sheets act as a barrier preventing grounding, which is why wrist straps are industry standard for safety, though Sechrist’s manual does not explicitly state that the mattress is a grounded surface.
Static electricity is always present and builds up more when the patient moves, Melnyczenko explained. If ungrounded, static moves from high concentration to low concentration and can discharge as a spark when a conductor touches a grounded surface.
Melnyczenko was asked about safety pauses again during Sharon’s cross-examination. He said they became industry standard around 2015 and must be documented. He said that from what he observed, safety checks were not consistently performed or documented at the Oxford Center.
When asked, Melnyczenko said that if there was no sheet between the patient and mattress, the patient would be grounded, but this is not considered proper grounding per NFPA 99 standards.
Melnyczenko did not see any prohibited items brought into the chamber and said it is impossible to know if flammable vapors were present. He concluded the fire was caused by static discharge because the patient was not grounded.
He explained that if the patient had been grounded, the static would have dissipated continuously, preventing the spark seen in the video.
Melnyczenko also noted differences between monoplace and multiplace chambers and claimed that some of the referenced articles included tests that did not fully replicate monoplace chamber conditions.
Troy Detective Ryan Whiteside testifies
Another person called to testify on Tuesday was Troy Detective Whiteside, who has 14 years of experience in digital forensics and video recovery, and investigated Thomas’ death.
He visited the Oxford Center on Jan. 31 to retrieve video evidence and coordinated with an Oxford representative to obtain footage from multiple camera angles of the incident.
An Oxford representative showed up to assist with retrieving video, and Whiteside said they sent the worker a link to a site where he could upload video files.
On Feb. 5, Whiteside executed a search warrant at Mosteller’s residence, recovering a cell phone and laptop, and on Feb. 12, he executed a search warrant at the Brighton location to access DVR systems.
When authorities originally went to the Troy location, the representative uploaded videos to the link, but told them that the actual video would need to be gathered at the Brighton location.
The detective explained that sometimes video is stored at a different location and accessed remotely, and they wanted to gather footage of Thomas’ treatments before the accident.
Once Whiteside arrived at the Brighton center, an IT worker told them that the video was actually stored at the Troy location, so he ended up going back to that location to retrieve DVRs and video files showing Thomas’ treatments from Dec. 9 to Jan. 31.
Reviewing Thomas’ treatment videos
Whiteside reviewed 35 treatment videos and noted Thomas never wore a grounding bracelet and mostly wore pajamas, sometimes using blankets fresh from the dryer.
He observed only one instance where Thomas appeared to be patted down before treatment; no other safety checks were evident, including on the day of the explosion.
During cross-examination, Whiteside also explained the digital evidence process, including the use of software to extract data from the defendants’ phones.
Whiteside said he did not see any sparks or damage in the videos before the incident and did not observe prohibited items brought into the chamber. He also noted that the video quality was insufficient to see if there were any sparks in the laundry machine.
The detective was also asked about text messages regarding cycle count numbers.
In a text sent in August 2023, Peterson asked Mosteller for the cycle counts, and he said the count for chamber 2 (where the explosion later happened) was at 17,988.
Then, in another text shown in court, Peterson asked him for the cycle count of the chambers again in November 2024, and Mosteller said that the chamber was at 19,585, which is below 20,000, Sharon noted during her cross-examination of Whiteside.
Sechrist Industries reported that it couldn’t perform maintenance on the chamber that had exploded because its cycle count was over 20,000 as of 2022.
“They further advised that they had written documentation between themselves and Peterson advising her that the cycle count on the chamber that had exploded was over 20,000 cycles when they were at the facility in 2022,” a detective previously said in a swear-to. “I reviewed photos of the chamber cycle counter from the date of the incident that were taken on scene, which showed that the chamber cycle count on that date was 19,894, which would be consistent with the rollbacks reported by ex-employees.”
Arriving at the ‘chaotic’ scene
The next person called to testify was Troy Detective Danielle Trigger. She testified that she was the on-call investigator on Jan. 31 and had overheard a dispatch run to the Oxford Center in Troy for a reported explosion.
She and other investigators responded to the scene and said they arrived shortly after EMS and road officers arrived at the scene.
She describes arriving at the scene as “chaotic,” and recalled “distraught” staff outside the center.
When she went into the center, she said firefighters were working inside a room that had three hyperbaric chambers, noting that the middle chamber, the one where the explosion had occurred, was “visibly very burnt.”
Trigger said what appeared to be a gurney was pulled out of that chamber, and the child’s body was “burnt severely” and “unrecognizable.”
While at the scene, Tigger said she didn’t interview Moffit, but said Peterson arrived a short time after law enforcement arrived at the scene. Shortly after that, Trigger said Mosteller arrived, and that she never saw Marken at the scene that day.
Trigger said she heard Peterson say the manufacturer had to get out there to figure out what had gone wrong “because they do everything by the book.”
Recovering items from the facility
At the scene, investigators recovered medical records, maintenance logs, and the user manual for the chamber involved. Trigger reviewed the manual and noted that the wrist grounding strap pictured was not used during the incident, as confirmed by video footage.
Trigger returned to the police department after attending the autopsy and continued reviewing records, determining that grounding wrist straps did not appear to be common practice at the facility.
During the investigation, Trigger drafted search warrants and recovered extensive training materials from the Oxford Center, including documents emphasizing fire prevention, safety protocols, and the critical importance of grounding patients with wrist straps.
One training manual warned that in the event of a fire in a monoplace chamber filled with 100% oxygen, survival chances for the patient are virtually nonexistent, underscoring the need for prevention.
The chamber that exploded was a monoplace chamber. Throughout expert testimony, we’ve learned that the concentration of oxygen that pressurizes multiplace chambers (Class A) is 21%, while the concentration of oxygen in monoplace chambers (Class B) is generally around 100%.
Other training materials and documents recovered had multiple sections that included making sure a grounding strap was secured, emphasizing the importance of one being used.
Trigger was also asked by Assistant Attorney General Chris Kessel to look at a picture from a document recovered at the Oxford Center, which was a photo of a child with hair that appears to be rising.
The detective said that video footage showed the boy’s hair rising just before the explosion, consistent with the buildup of static electricity.
Grounding wrist straps found in ‘junk drawer’
She noted that grounding wrist straps were found unused in a drawer at the facility that she described as being a “junk drawer,” as it also contained half-eaten bags of chips and tape.
Trigger said the wrist straps appeared as though they hadn’t been used or touched in some time.
Certification isn’t required to operate a hyperbaric chamber in Michigan. Trigger testified that Mosteller had a current certification, though. Multiple attorneys objected to this testimony, saying it wasn’t relevant because certification isn’t required in the state, but the judge found the information to be relevant, since those certified would have had to be exposed to training materials, which she said is relevant to the case.
Questions about evidence being shared
Trigger also explained how detectives upload materials related to investigations into Evidence.com, which allows them to create a link to share with others, including prosecutors and defense attorneys.
Then, if additional items are added, detectives are prompted with the opportunity to share new items with any party who previously received the link.
Since Trigger first created and shared the link to the materials, she said about eight or nine items were added, including information about bond violations for one of the defendants, the fire report, the autopsy report and supplemental reports that were created after a taint team reviewed electronic devices.
Although Trigger sent the updated links to the defense attorneys, they said they never received them. This appeared to be some sort of glitch with the platform, since the detective had verification on her end that it was sent.
Kessel said the attorney general’s office personally sent some of the documents to the defense attorneys, including the autopsy report and the fire report, so they should have most of the materials.
Cycle counts, maintenance records
During Trigger’s cross-examination, questions about cycle counts on the chambers came up, and the detective was asked about how she investigated the chambers.
Todd Flood, Marken’s attorney, asked her if they had discovered whether any of the chambers had done 3,000 cycles in a four-month period, and Trigger said they only investigated the chamber where the explosion occurred, but the facility didn’t keep a log of the chambers, so she couldn’t speak to how many cycles were done in that time period.
Alona Sharon, Mosteller’s attorney, asked her about finding wrist straps, as well as about the number of dives (treatment sessions) that had been done on the chamber where the explosion occurred.
Trigger said that in the span of nine years, the chamber accrued over 20,000 dives, based on the evidence.
Additionally, a maintenance record from December 2022 indicated that Sechrist Industries, the manufacturer of the chambers, said they would no longer service the chamber because it had over 20,000 dives.
The preliminary examinations are scheduled to continue on Dec. 12, and the cross-examination of Trigger will continue.