The lead fire investigator took the stand as testimony continued on Tuesday to figure out what caused a Michigan hyperbaric chamber explosion that led to the death of 5-year-old Thomas Cooper back in January.

The four suspects — Tamala Peterson, Gary Marken, Alita Moffitt and Jeffrey Mostellar — are accused of not following safety protocols while working at the Oxford Center in Troy earlier this year. One of the biggest arguments that remains in this case is the use of grounding straps.

When the defense asked if grounding straps could have reduced the likelihood of ignition, Troy Fire Deputy Fire Chief Shawn Hugg said, "I believe so, yes."

During the fourth day of the case's preliminary examination to determine whether all four of the defendants will go to trial, Hugg shared how he came to the conclusion of the cause of the explosion and how it may have been avoided.

"Through the use of a grounding strap on the patient, he would have been at the same electric potential as all the loaded conductors within the chamber and therefore would not have created the differential potential should we become charged with static electricity," he testified.

During cross-examination, defense attorneys for Peterson and Moffitt asked questions about how the deputy fire chief reviewed the evidence and what may still need to be analyzed.

"The fact is that you haven't yet analyzed any sample that might come from the oxygen tank to see whether or not there may have been some impurity in the oxygen tank, right? You haven't done that, right?" asked a defense attorney.

"That is correct," said Hugg.

With Judge Maureen McGinnis expecting the investigator's testimony to take a full day, no other witnesses were set to appear before the court on Tuesday.

After a break for the holidays, the preliminary examination is expected to continue on Jan. 12, 2026.