On August 27, 2021, a PDM3700 caught fire underground at the Warrior Met No. 7 mine. This photo was taken during the A&CC investigation. (Photo: MSHA)

The agency should have issued a Safety Alert years ago

By Steve Fiscor, Editor-in-Chief

On May 9, 2024, the U.S. Mine Safety and Health Administration issued a Safety Alert for Continuous Personal Dust Monitors (CPDMs). The Alert warned that the CPDMs could burn in certain events. It was apparently based on an incident that occurred almost a month prior.

In that incident, the agency said, a CPDM was placed on top of a continuous miner and was struck by a rock (approximately 24-in. diameter and 10-in. thick) that fell approximately 6 feet on April 11, 2024. Miners reported that, immediately after impact, flames erupted from the device, followed by an explosion and larger flames encompassing the unit for a short period of time.

The agency waited for nearly a month to make that announcement, but it wasn’t the first time this has happened.

In an internal memo, distributed on December 7, 2021, electrical engineers from the Electrical Safety Division of MSHA’s Approval & Certification Center (A&CC) answered a request for technical assistance regarding a Thermo Fisher Scientific PDM3700 recovered from a “non-reportable fire” at the Warrior Met Coal No. 7 mine in Alabama. The memo stemmed from a request for technical assistance by MSHA’s Birmingham District. The District sought help in the investigation of the PDM3700, which had reportedly caught fire while inside a pocket of a nylon work vest on August 27, 2021.

The vest was not being worn at the time, and the fire was extinguished with a portable fire extinguisher in a working section of the underground mine. The Birmingham District asked the A&CC to determine the cause of the fire.

The Alert and the memo show that MSHA has known for more than two years that there was a problem with these units, but it did not disclose it publicly until the second occurrence. The internal memo and other information related to the faulty CPDMs were daylighted through a Freedom of Information Act (FOIA) request.

Lithium-ion batteries are used in many devices that are taken underground. Some of these devices and
instruments are taken past the last open crosscut, which is why they must be approved by MSHA as intrinsically safe. MSHA asserts that when designed, manufactured, used and maintained properly, Li-ion and other battery sources used for approved devices are safe. In the Safety Alert, the agency advised coal operators on safe use, but they also said users should “keep fire extinguishing equipment readily available.” If a coal miner must keep a fire-extinguisher handy, are the CPDMs intrinsically safe? The PDM3700 is the only approved unit that coal operators can use to comply with the agency’s current respirable dust regulations. The estimated cost of a PDM-3700 is approximately $22,000 and collectively the U.S. coal industry has spent $60 million or more to purchase 2,500 to 3,000 of these instruments.

Chad Huntley, an electrical engineer for MSHA, was an acting supervisor who was involved in the investigation of the Warrior Met CPDM that caught fire. He believed strongly enough that MSHA should have issued a warning to the coal industry that he brought it to the attention of U.S. Sen. Shelley Moore Capito (R-WV). The A&CC is in Triadelphia, W.Va.

When Assistant Secretary for Mine Safety and Health Chris Williamson, responded to questions about the faulty CPDMs and the approval process raised by Sen. Capito, the agency realized it had a problem and then the second unit caught fire.

A&CC investigators determine the fire originated from the battery compartment. (Photo: Thermo)

The A&CC Investigation Stops Short

The Alabama District specifically asked the A&CC to determine the cause of the fire. In the memo, the A&CC said it determined the fire originated in the battery compartment of the CPDM, but they did not determine what caused it. The investigation appeared to stop short of drawing a conclusion related to the Li-ion batteries even though MSHA accident investigation protocol stresses that the agency should strive to find the root cause.

When Sen. Capito asked: What has been done to warn the mining industry of potential hazards related to the CPDM? Williamson answered: “MSHA was not able to determine the cause of that fire and has no reason to believe the CPDM is not safe to use. MSHA did not have a basis for issuing a Safety Alert regarding the fire or the CPDM, as the MSHA investigation did not reveal a fault with the MSHA process or with the CPDM.”

Williamson’s response to Sen. Capito was dated March 15, 2024. The second known incident occurred on April 11, 2024, and MSHA issued the Safety Alert.

More Questions Than Answers

Williamson’s response to Sen. Capito seems to raise more questions than it answered, Huntley said. As an example, Willamson said: “MSHA was not able to determine the cause of that fire and has no reason to believe the CPDM is not safe to use.”

Both units caught fire underground. “If MSHA doesn’t know what caused the fire, one would think that the agency would err on the side of safety and take the CPDM out of service until they determine the root cause, but they have not done that,” Huntley said.

Williamson also said: “MSHA did not have a basis for issuing a Safety Alert regarding the fire or the CPDM, as the MSHA investigation did not reveal a fault with the MSHA process or with the CPDM.”

This statement is true, Huntley explained, because the A&CC determined the fire originated in the battery compartment and did not determine the root cause.

The PDM3700 battery pack has 10 cells. Because a Li-ion fire, or thermal runaway, is so powerful and hot, all the evidence may have been destroyed. “If that were the case, MSHA could not with 100% certainty say what caused the fire, but they should have been able to draw some strong conclusions,” Huntley said. “The agency could have said it’s not 100% certain, but the Li-ion batteries were likely the source.”

Had MSHA interviewed the roof bolter operator, he could have helped rule out whether the device was impacted, Huntley said. “He could have also said the unit just caught fire.”

Could a cell short circuit? What about the charging process? Overcharging can damage these batteries. Exposure to heat can also damage them.

MSHA stopped short of saying the device was faulty. In his response to Sen. Capito, Williamson said: “Since the CPDM was fully implemented in mines in February 2016, MSHA has only been notified of a single fire involving the CPDM.”

Isn’t one fire, one too many, Huntley asked.

“The investigation…. into the Warrior Met No. 7 Mine did not reveal any issues with the CPDM, or with the battery, that contributed to the incident,” Williamson said.

How can he say that when the agency doesn’t know what caused the fire inside the compartment, Huntley asked.

“While the investigation conducted by the [A&CC] indicates that the fire originated in the battery compartment of the CPDM, the investigators could not determine the initial ignition source. In other words, while not verifiable, it is suspected that the CPDM could have been damaged such that the battery compartment was vulnerable to outside ignition sources,” Williamson said.

The A&CC report does not mention the possibility of an outside ignition source. It doesn’t offer non-verifiable suspicions and it shouldn’t, Huntley explained. “Why would MSHA administrators talk about
suspicions that are not verifiable,” Huntley asked.

The fire with this unit at Warrior Met involving an MSHA-approved product deserved a Safety Alert, Huntley said. The only people outside of MSHA who were aware of this fire were those at the Warrior Met mine. The mines in Alabama are deep and gassy and, if a CPDM fire were to occur, these operations would be more susceptible to a larger hazard such as a mine explosion.

The PDM3700 is larger than the traditional cap lamp. (Photo: Thermo)

The A&CC Investigation

The A&CC issued Approval No. l 8-A140015-0 on December 4, 2014, to Thermo for the PDM3700. The original approval included a battery pack comprised of Panasonic (Sanyo) Li-ion 18650 cells. In January 2020, Thermo added an alternate battery pack to the product’s approval, an LG Corp. Li-ion 18650 cell.

On September 2, 2021, the A&CC received the CPDM from Warrior Met with one loose cell from a battery pack and the 3M nylon work vest. Thermo confirmed that the PDM3700 was manufactured in October 2015. Thermo’s May 2020 service records show that they changed the battery pack to the LG 18650 Li-ion cells.

The investigators conducted a detailed inspection of the CPDM, loose cell, and 3M nylon work vest. The investigators took photographs while removing charred material and disassembling the CPDM components to record the process. Coal Age believes the photo time stamped 9/17/2021 is the PDM3700 that caught fire at Warrior Met.

The A&CC investigators noted that the PDM3700 exhibited extensive fire damage, mostly around the battery compartment. The back cover case material around the battery compartment had melted. A few small areas burned and melted through from the battery compartment into the electronic compartment containing the the mass transducer, and through the front cover.

The A&CC investigators noted that the manufacturers datasheet indicated the melting specification of the PDM3700 case material was 221°C. Therefore, the investigators concluded that the heat of the fire was greater than this temperature. The concentration of the heat and fire damage to the battery compartment and minimal heat and fire damage to the material in the electronic and mass transducer compartments led to the conclusion that the initial stage of the fire occurred in the battery compartment.

The A&CC investigators also noted that the case of the single loose cell was ruptured along its length and its internal material was fire-charred and friable. The length and diameter of this cell was consistent with the size of an 18650 type Li-ion cell and could have been a cell manufactured by LG or Panasonic. The investigators could not determine from the evidence the initial ignition source involving this cell or cells from the CPDM battery pack.

The nylon work vest was reportedly hanging from a roof bolting machine with the CPDM inside a pocket when the fire occurred. The rear inside pocket of the vest exhibited melting on the bottom area of the vest pocket consistent in size with the dimensions of the PDM3700.

The data downloaded from the day of the incident for the Warrior Met PDM3700 did not show any unusual trends when compared to other data sets analyzed from the same unit. These other data sets were from normal mine use in the year prior to the fire. The last recorded line of data occurred at the presumed time of the fire (2:36 a.m. CST on August 27, 2021) and showed an error code of “CPU RESET.” Thermo identified the “CPU RESET” code as an error code that would occur when power was lost to the CPDM.

The investigators determined that the PDM 3700 was assembled according to the approval drawings on-file with MSHA.

The concentration of the heat and fire damage to the battery compartment and minimal heat and fire damage to the material in the electronic and mass transducer compartments led the A&CC investigators to conclude that the initial stage of the fire occurred in the battery compartment. The investigators said they could not determine from the evidence the initial ignition source involving this cell or the other nine cells from the CPDM battery pack.

The Power Source

The PDM3700 has one battery pack assembly that Thermo says should be replaced when its capacity diminishes. According to the manufacturer, the PDM3700 battery pack (PN: 56-010897-2300) is designed with specific individual battery cells. These battery cells are not user replaceable. The battery packs may be replaced only by MSHA certified individuals pursuant to 30 CFR Parts 70, 71 & 90.

Thermo tells the users that the battery packs should be charged while installed in the PDM3700 and in fresh air in battery charging stations as defined in 30 CFR 75.340 or fresh air above ground. Thermo explains that it requires about six hours to fully charge the instrument, it does not warn the user about overcharging the battery packs.

Thermo states repeatedly on all the product information related to the PDM3700 that, if the case is damaged or otherwise compromised, it should not be placed into service. Whenever the PDM3700 case is opened, Thermo advises the users to perform a case-leak check after reassembling the case. The system must pass the case-leak check prior to operating the instrument. The leak must be fixed, and the instrument must be re-tested if the leak check does not initially pass. Users must not operate the instrument if the system does not pass the case leak check.

MSHA implemented a more stringent dust policy in 2014. Mine operators were offered one device manufactured by Thermo to comply with the policy. From 2016 to 2020, no incidents were reported. In 2020, Thermo switched from Panasonic to LG 18650 Li-ion batteries. A year later a PDM3700 catches fire at Warrior Met.

Why Did MSHA Drag Its Feet?

In his letter to Sen. Capito, Williamson also said: “Huntley contributed technical input to the investigation and was involved in reviewing the report. At that time, Huntley concurred that neither the CPDM nor CPDM battery could be identified as the cause of the ignition.” Williamson said. Huntley did not indicate he believed the CPDM or the battery pack were hazardous products; recommend that either the CPDM or the battery pack should be removed from service; suggest that MSHA should notify the mining community of a potential fire hazard related to CPDM use; or recommend changes to either the CPDM design or the MSHA product approval process.

“I was an acting supervisor from mid-September to late December 2021,” Huntley said. “This period covered almost the first four months after the CPDM fire at Warrior Met 7 in Alabama. I know the accident investigators who were conducting the investigation and trust their professional judgment. It was my assumption that MSHA would attempt to determine the facts leading up to the fire.

On December 7, 2021, the accident investigators sent a memo to Alabama District Manager Mary Jo Bishop copying Huntley’s supervisor Patrick Retzer and A&CC Center Chief Juliette Hill, saying the investigation determined that the fire occurred in the battery compartment. The memo said the investigators could not determine from the evidence the initial ignition source involving this cell or the other nine cells from the CPDM battery pack.

At that time, Huntley said he was toward the end of his stint as an acting supervisor. Huntley said he has more than 25 years of experience as an electrical engineer at A&CC. “Based upon my experience and knowledge of MSHA policies, procedures, regulations, etc., MSHA would have continued its investigation,” he said.

“The memo from the investigators would have been a starting point, not the end of the line as it came to be,” Huntley said. “I did not see the need to provide my recommendations because the investigation appeared to be on-going.”

On June 17, 2022, Huntley emailed Retzer and the other employees in his group. “While we’re on the topic of lithium batteries, do we have any plans of addressing the CPDM fire that appears to have started in the lithium battery compartment or to look into it further to figure out what started it,” Huntley wrote. “It doesn’t look good to have an IS [intrinsically safe] permissible product appear to be the source of a fire which violates the definitions of both ‘permissible’ and ‘intrinsically safe.’”

Huntley said another coworker relayed information to the group on July 13, 2022, from Thermo in which Thermo said it believed the Warrior Met 7 CPDM fire was an isolated incident.

MSHA has given Thermo special treatment, Huntley explained. “MSHA personnel, including the IS group, met with Thermo monthly starting around 2018, which is a privilege not given to other MSHA A&CC applicants,” Huntley said. “IS personnel have no other monthly meetings with any other customers/applicants. A general rule of thumb is that MSHA A&CC will only offer customers/applicants a 1-hour free consultation per product/application while Thermo has been given many hours (estimated to be hundreds of hours) of free consultation over the years. The special treatment for this product continues.”

“Deciding whether or not to notify the mining community was not within my purview,” Huntley said. “It is among the responsibilities of the A&CC Center Chief, District Managers, or MSHA Headquarters. It is offensive that Williamson tried to give Sen. Capito the impression that MSHA would have demanded a redesign of the CPDM, a change in the battery source, or notify the mining community if I would have made these recommendations. I am at the bottom of the totem pole, seven levels below Williamson.

“The units need to be taken out of service before an ignition, fire or explosion occurs,” Huntley said.

“More importantly, MSHA needs to alert the industry about faulty equipment as soon as possible,” Huntley said. “The MSHA I once knew would never have hesitated to issue a Safety Alert when miners’ lives were at risk.”