Nickel-Metal Hydride (NiMH) Batteries and Their Incompatibility with Hyperbaric Oxygen Therapy (HBOT)

Nickel-Metal Hydride (NiMH) Batteries and Their Incompatibility with Hyperbaric Oxygen Therapy (HBOT)

1. Overview of NiMH Batteries

NiMH (Nickel-Metal Hydride) batteries are a rechargeable battery type commonly used in:

• Consumer electronics (cameras, radios)
• Medical devices (older models)
• Emergency lighting
• Electric razors and portable monitors

Composition:

• Positive Electrode: Nickel oxyhydroxide (NiOOH)
• Negative Electrode: Hydrogen-absorbing metal alloy
• Electrolyte: Potassium hydroxide (KOH) – a highly alkaline, conductive solution
• Typical Voltage: 1.2V per cell

2. Thermochemical Risks in HBOT Environment

NiMH batteries, while more stable than lithium-ion, still present serious hazards in a hyperbaric oxygen environment due to the following:

A. Electrolyte Risk

• The KOH electrolyte is caustic and chemically reactive, posing severe tissue injury risk if leaked.
• Under high pressure and oxygen-enriched conditions, leakage or venting can accelerate corrosive reactions and combustion if sparked.

B. Internal Pressure Build-up

• NiMH cells generate internal gas pressure (mainly hydrogen and oxygen) during overcharge, deep discharge, or abuse.
• In a pressurized oxygen-rich environment, any failure can cause explosive venting or ignition.

C. Electrical Arc and Spark Hazard

• Although less likely than Li-ion batteries, a faulty cell or shorted contact in NiMH still has the potential to arc or spark, which is unacceptable in oxygen-enriched atmospheres.

D. Non-Intrinsically Safe

• NiMH battery packs are not manufactured or certified as “intrinsically safe” for use in Class I, Group A (acetylene) or Group B (hydrogen-rich) oxygen-enriched atmospheres as defined by NFPA 99.
• This lack of intrinsic safety design (no spark arrestors, no pressure vent redundancy) violates hyperbaric safety standards.

3. Regulatory and Safety Standards

• NFPA 99, Chapter 14: Strictly prohibits non-approved electrical devices, including any unsealed or non-tested batteries, inside Class A or B hyperbaric chambers.
• ASME PVHO Guidelines: Reinforce exclusion of devices that can produce heat, arcs, or flames.
• UHMS Guidelines: Advise against any battery-powered device inside the chamber unless tested and approved.

4. Conclusion: Why NiMH Batteries Are Unsafe in HBOT

Summary: NiMH batteries, despite their relative safety in normal environments, are unacceptable in HBOT due to their chemical, electrical, and regulatory risk profiles. No untested or unshielded battery — including NiMH — should be permitted in an oxygen-enriched pressurized chamber.