INTRODUCTION

Overview

Safety must be the cornerstone of every hyperbaric oxygen therapy (HBOT) program. Documented hyperbaric disasters have repeatedly shown that strict adherence to safety protocols - especially routine safety checks - is critical to the safe delivery of HBOT. [1]

It is imperative that the integrity of the patient grounding system be verified prior to each treatment session. [1]  This topic provides a comprehensive overview of the technical operations involved in patient grounding - an essential aspect of HBOT safety.

Background

In January 2025, a tragic fire occurred in a monoplace chamber in the United States, resulting in the death of a 5-year-old patient. An investigation by the state's Attorney General revealed that essential safety practices had been neglected. The most egregious oversight was the failure to ground the patient in a monoplace chamber pressurized with 100% USP medical oxygen. [2] 

In July 2025, another accident took place in a monoplace chamber in the United States: a 43-year-old physical therapist was found dead inside a hyperbaric oxygen chamber at his health clinic in Arizona, after  the intact hyperbaric chamber appeared to have had a flash fire.  [3]

To prevent such accidents, daily inspection of hyperbaric chambers is essential before initiating treatment. This includes thorough testing of all grounding systems. Grounding procedures consist of three main components:

• 1. The patient wrist strap
• 2. The patient ground connection to the chamber hull
• 3. The chamber’s connection to the hospital's grounding system

The Undersea and Hyperbaric Medical Society (UHMS) urges all HBOT providers to review and adhere to current safety standards and codes to ensure full compliance.

The U.S. Food and Drug Administration (FDA) has also advised patients seeking HBOT to choose facilities accredited by UHMS. Such accreditation reflects a facility’s demonstrated commitment to safety and excellence. [4]  Accredited hyperbaric centers must document and verify adherence to critical safety protocols, including the elimination of electrical and static hazards through appropriate grounding practices. [4]

Definition

• Grounding:  the term used to describe the process of electrically connecting something to earth.  [1]
• Grounding is accomplished by physical contact with a conductive material that has electrical continuity to earth. This procedure is the most reliable way to eliminate static charge. 
• Common ground of a building: the terminology used for the practice of every grounding wire throughout a building being tied to a single earth ground.  
• Common ground is the standard for hospital buildings in the United States. 
• It is important to know that throughout the world, the reliability of grounding systems in buildings will vary.  [1]

Relevance

• Implementing grounding protocols is a key component of comprehensive hyperbaric safety programs and is required by the National Fire Protection Association (NFPA) regulatory standards.  [5]
• Proper grounding minimizes the accumulation of static electricity and reduces the likelihood of accidental sparks and mitigates the risk of fire.
• While oxygen itself is not flammable, it is an oxidizer that supports combustion and can increase the flammability of other materials. Since oxygen-enriched environments offer conditions for a fire to grow rapidly, care must be taken to prevent any means of ignition from entering an oxygen-enriched environment such as a hyperbaric chamber.  [6]
• Static discharge or electrical sparks whether inside or near the hyperbaric chamber can serve as an ignition source with potentially catastrophic consequences.
• Failure to adhere to proper grounding protocols poses significant risks, including:
• Chamber fire and explosion
• Injury or death to patients and staff
• Facility infrastructure damage
• Potential criminal charges for administrators and staff

Static Electricity 

• Static electricity: is an electrical charge created by the accumulation of free electrons. 
• Free electrons: electrons become free when friction tears them from their atoms or when dissimilar materials contact and then separate from one another. Examples of situations which may result in free electrons are: 
• Fabrics rubbing together
• Skin rubbing against fabric
• Shoes moving across flooring/carpet
• Friction of something moving through air 
• Electrical charge will build on the surface of a material as free electrons accumulate. When the charge builds high enough, a spark will jump to earth (or to another material):  [1]
• All textiles are capable of generating static electricity and some materials tend to generate more static electricity than others. 
• Silk, wool, and synthetic textiles are examples of materials known to generate more static electricity. These materials are not suitable for the hyperbaric environment and are prohibited for safety reasons.
• Cotton is a material that generates little static electricity and for this reason is the material of choice for HBOT patient garments worn in a hyperbaric chamber.

Controlling Static Charge 

• There are two considerations when attempting to reduce or eliminate static electricity:
• 1. Select materials that generate less static charge  See section “ Static Electricity” above.
• 2. Provide static charge a pathway to earth by using conductive materials.  [1] 
• Humidity: humidity provides a flow path for static charge because water is conductive.
• In general, high humidity in a chamber means less static accumulation; and low humidity in a chamber means more static accumulation.
• At a relative humidity of 65% or greater, a material should not accumulate static charge. The lower the relative humidity, the more static charge can accumulate.
• High chamber flow rates (e.g., 450 lpm) have an impact on relative humidity. Reducing the chamber flow rate (e.g., 240 liters per minute or lpm) will lead to an increase in relative humidity within the chamber.  [7]
• Humidity levels in hyperbaric chambers vary greatly depending on several factors including the chamber air intake compressor system, ventilation, and even the size of the patient.  [1]
• Because of the variables involved, humidity is generally not a reliable way to control static electricity in a hyperbaric chamber.  [1]
• Grounding system for the building: the preferred way to ground a hyperbaric chamber and therefore control static electricity is with the grounding system for the building if it is reliable (rather than the chamber having a separate earth ground).
• Separate earth ground for the chamber: if the grounding system for the building is unreliable, a separate earth ground for the chamber might be used.  [1]

Regulatory Guidelines

NFPA

The National Fire Protection Association (NFPA) code for hyperbaric facilities (NFPA 99 2024 edition) has specific requirements for grounding:

• 14.3.1.6.3.1:  antistatic procedures, as directed by the safety director, shall be employed whenever atmospheres containing more than 23.5 percent oxygen by volume are used.   [5]
• 14.3.1.6.3.2:  in Class A and Class B chambers with atmospheres containing more than 23.5 percent oxygen by volume, electrical grounding of the patient shall be ensured by the provision of a high-impedance conductive pathway (resistance) in contact with the patient’s skin.   [5]
• 14.2.9.4.1:  all chamber hulls shall be grounded to an electrical ground or grounding system.  [5]
• 14.2.9.4.1.3:  the resistance between the grounded chamber hull and the electrical ground shall not exceed 1 ohm.  [5]

UHMS 

According to the UHMS Clinical Hyperbaric Facility Accreditation Manual, Fourth edition:  

• HBOE 3.3.1.2:  the integrity of the electrical ground of a Class B monoplace chamber is verified prior to each patient treatment.  [5]

The UHMS safety guidelines to eliminate electrical and static hazards include recommendations to  [8] :

• Exclude all electrical or static-generating devices from the chamber
• Conduct a procedural "time-out" before each treatment to confirm the patient’s identity, treatment plan, and safety readiness
• Take extra precautions for pediatric patients or those with cognitive impairment, including physical checks when warranted
• In monoplace chambers using 100% oxygen, patients should wear grounding straps to eliminate static discharge risks.

TECHNICAL OPERATIONS

Patient Safety

Wrist Straps

• Occupants in a hyperbaric chamber are grounded to protect them from producing static by wearing a wrist strap.
• The wrist strap, which can be made of either metal or an elastic band, is attached to a coiled wire that serves as a high-resistance conductive pathway.
• The resistance across the wrist strap is intended to be one million ohms (1MΩ ).
• Use of a wrist strap is common practice in monoplace chambers which are typically filled with oxygen.  Wrist straps are rarely, if ever, employed in multiplace chambers which are filled with air.  [1]
• Use of a high-resistance pathway (resistance) to ground people is the standard practice of the electrostatic discharge industry.

Testing Ground Continuity 

Common Points of Ground Testing

• The same principles of ground testing apply to both monoplace and multiplace chambers. However, some issues (e.g. patient grounding, wrist strap testers) are not typically encountered in multiplace chambers. In order to address all grounding issues, a monoplace chamber is used to illustrate ground testing procedures. The testing points and techniques are similar for all brands and models of monoplace chambers. Figure 1 and Video 1 illustrate a grounding continuity test. 
• An ohmmeter is an instrument for measuring electrical resistance, which is expressed in ohms (1Ω)
• A handheld ohmmeter uses a small electrical current to check the continuity of a circuit and is the device used for grounding tests in the HBOT environment (Figure 2).
• The meter has two probes that provide a measurement in ohms (1Ω) of resistance when the probes are touched to different points (i.e. wall ground stud to chamber frame).  

Figure 1.   Grounding continuity test  

Figure 2. Grounding test with ohmmeter

Chamber Ground

• Monoplace chambers are typically grounded by means of a thick wire connecting some point on the metal shell of the chamber to a ground stud on a nearby wall.
• Inside the wall, the ground stud is connected to either common ground for the building (preferred) or to a separate earth ground.
• The NFPA 99 specification for resistance of this ground is no more than one ohm (1Ω ).  [1]

Patient Ground to Chamber

Test for continuity from the common ground for the building stud on a nearby wall to the patient grounding point on the chamber (wrist strap socket).

• If this socket is mounted directly to the metal framework of the chamber, there should be less than one ohm (1Ω) of resistance between this point and the common ground for the building.
• This grounding test assures that the wrist strap will have a ground path when connected. [1]

Patient Ground to Chamber Bed

If the wrist strap socket is on the chamber bed, the measurement between the wrist strap socket and the common ground for the building will likely be more than one ohm (1Ω) of resistance.

• The wheels on the underside of the chamber bed will have variable resistance because of variable contact of the axles with the inside of the wheels and variable contact of the wheels with the chamber rails. If the chamber bed is made up of multiple parts bolted together, the bolts can become loose and increase resistance through the frame of the bed. The goal in this case is to ensure the bed does not interfere with the patient ground path. [1]
• There is no guidance on the acceptable amount of resistance through the chamber bed, because NFPA 99 does not specifically address it. However, it is logical to assume that if the wrist strap has one million ohms (1 MΩ) of resistance by design, it would be acceptable for the bed to have as much as one million ohms (1 MΩ) of resistance. [1]

Chamber Bed Ground

• When the bed is part of the patient ground path, it should be tested frequently. The test is performed by loading the bed into the chamber, then touching one ohmmeter probe to the wrist strap socket and the other probe to common ground for the building (or to the chamber rail).  [1]
• Even when the patient is not grounded through the chamber bed, the bed itself should be grounded to prevent it from building up static charge. NFPA 99 has no specific guidance on the acceptable amount of resistance. [1]
• However, the guideline "NFPA 77: Recommended Practice on Static Electricity" discusses the desired limits of resistance for grounding of conductive equipment. [9] It recommends a resistance of one million ohms (1 MΩ) or less. [9]
• The test is performed by loading the bed into the chamber, then touching one ohmmeter probe to a conductive point on the frame of the bed and the other probe to the common ground for the building (or the chamber rail).
• The amount of weight on the bed will change the resistance.
• More weight will press the wheels tighter against the chamber rails.
• The same effect can be illustrated by holding the ohmmeter probes loosely then tightly with your fingertips.

Patient to Wrist Strap

• The continuity between the patient's skin and the wrist strap socket should be tested prior to each treatment. NFPA 99 does not offer any specific guidance on the frequency of this testing. [1]
• Moistening the patient's grounding strap with normal saline can improve the connection with the patient’s skin.
• It is essential to develop and implement procedures for actions to take if the patient's ground strap becomes disconnected. Recommended actions include:
• Having the patient lie still, then safely ascending them, removing them from the chamber, and reconnecting the ground strap.
• This procedure aims to prevent the patient from moving around in search of the strap, which could potentially cause an electrostatic build-up and discharge.

Patient Ground-Check Instructions per Manufacturer

• Check with the chamber and wrist band manufacturer for specific patient ground-check instructions, search Hyperbaric Oxygen Chambers in the “Product Navigator” tool.

Video

Video 1. Checking chamber ground from wall to chamber and wall to grounding bracelet (Southeast Iowa Regional Medical Center's technique)