Reducing the Burn in Oxygen Delivery Systems

Minimize the oxygen concentration, control ignition sources, and maximize fire-resistant materials 

A patient went into an operating room to have a neck mole removed but came out with second-degree burns across their face. How could a common surgical procedure go wrong like this?

Of the approximately 550 to 600 surgical fires that occur each year, about 75% involve oxygen-enriched environments. When supplemental oxygen is administered to patients, it can result in localized oxygen enrichment, particularly around the patient's head, neck, mouth, and breathing pathway. Oxygen can also become trapped and accumulate underneath equipment like medical drapes that may be placed over the patient.

In the case of the neck mole removal that resulted in second-degree burns, the patient was administered medical oxygen through a nasal cannula, and the surgeon began using an electrocautery tool. A spark from the device reacted with oxygen leaking from the nasal cannula, igniting surgical drapes near the patient and melting the cannula, which adhered to the patient's face, causing the burns.

Because devices like electrocautery tools are designed to produce high temperatures, they can readily ignite combustibles (such as artificial tissue or medical-grade liquids and solvents) used near the nasal cannula in the presence of elevated oxygen levels. Once ignition occurs, a fire can rapidly spread to other combustibles, including the plastic tubing of the oxygen delivery system and surgical drapes on the patient. 

Manufacturers of oxygen systems for hospitals, clinics, hyperbaric chambers, or at-home use can reduce oxygen-related fire risks by conducting oxygen compatibility assessments of the components used in their systems. 

The fire hazards associated with localized oxygen-enrichment are not limited to the operating room. Medical treatments involving hyperbaric chambers or at-home oxygen therapy can also result in localized oxygen-enriched environments that increase potential fire risks. Preventing fire accidents in these settings requires minimizing the concentration of oxygen being administered and controlling ignition sources through a multidisciplinary approach involving design engineers, regulatory agencies, risk managers, and healthcare professionals.

Identifying ignition sources and understanding the local oxygen environment

Identifying ignition sources can be complex, as a variety of sources may be present in a single context. In the operating room, ignition sources could include lasers, non-rated light sources, electric drills, electrocautery tools, defibrillators, and others. In clinical hyperbaric chambers, ancillary devices are typically the most common cause of fires, where medical products can serve as unintended ignition sources via electric arcing, electrostatic discharge, frictional heating, electric heating, or exothermic reactions. For home oxygen therapy systems, smoking materials are the leading cause of fire fatalities, according to a recent National Fire Protection Association (NFPA) study.

NFPA noted that while sprinklers and smoke alarms play an important role in fire protection systems, oxygen-enriched fires burn more intensely and spread more rapidly, making prevention critical. Other factors that make reducing oxygen-related fire risks challenging include understanding the local oxygen environment. 

• Estimating the local oxygen concentration: During therapy, the administered oxygen may not be completely metabolized by the human body, creating an oxygen-enriched environment around patients as they exhale. In many cases, measuring or estimating these local oxygen concentrations is challenging given the complexity of how each individual's respiratory system absorbs oxygen, variability in the settings where patients receive supplemental oxygen therapy, and the available instrumentation, which focuses on the concentration of oxygen in the bloodstream, not in the surrounding air.
• Oxygen index: The minimum oxygen concentration required to sustain the combustion of a non-metal material at room temperature and ambient pressure is known as the oxygen index. It can be determined using standardized testing techniques such as ASTM D2863 or ISO 4589-2. Testing results have shown several examples of materials that only require slight to moderate enrichment (oxygen indices between 21 and 30%) to support combustion.

Stopping the burn

Multidisciplinary approaches can be extraordinarily valuable in anticipating and effectively mitigating potentially deadly fire risks. Fire investigators perform forensic failure investigations in residential, commercial, and industrial settings to determine the origin and cause of a fire according to the guidelines provided in NFPA 921 (Guide for Fire and Explosion Investigations). Manufacturers can use findings from these investigations to reduce or mitigate potential fire risks in their oxygen supply systems, as well as educate medical providers and patients who use medical oxygen supply systems. 

Manufacturers of oxygen systems for hospitals, clinics, hyperbaric chambers, or at-home use can reduce oxygen-related fire risks by conducting oxygen compatibility assessments of the components in their systems. In an oxygen compatibility assessment, the ignitibility and flammability of each component is evaluated under in-use conditions. The assessment also evaluates the ability of an incipient fire to spread and potentially cause a breach in the system. By systematically evaluating each component's ignitibility and flame spread behavior, manufacturers can confirm their system designs are robust and resilient to potential ignition mechanisms.

Manufacturers and other stakeholders also often have the option of designing and building safeguards into their products. Thermal fuses are one example of a safety device that can mitigate the fire risk of medical oxygen therapy delivery systems. Currently, the U.S. Veterans Health Administration requires the use of thermal fuses on all home-oxygen therapy systems. The American Burn Association and the International Association of Fire Chiefs both recently published position statements supporting the use of thermal fuses in home oxygen delivery systems. In Europe, adding thermal fuses to oxygen delivery systems has greatly reduced home-oxygen therapy incidents and fatalities, and one U.S. study found that a national mandate for thermal fuses would be a cost-effective solution towards preventing oxygen-related fires. 

A thermal fuse cuts off the flow of oxygen when downstream delivery equipment (such as tubing or the cannula) ignites, thereby preventing the propagation of the flame towards the oxygen source. By interrupting the oxygen supply, the combustion of the ignited fuels is less energetic, and the ignition propensity of nearby combustibles can be drastically reduced, mitigating further spread of the fire and limiting the potential consequences.

When designing consumer and medical products that utilize medical oxygen, conducting rigorous assessments that account for codes, standards, and industry best practices can help manufacturers minimize fire hazards and improve patient safety. These standards aim to help manufacturers and industry users of oxygen systems evaluate potential fire risks; understand the ignitability and flammability of their materials and maximize their use of ignition resistant materials; analyze objectives and constraints on their systems to minimize any hazards associated with a design; and utilize and incorporate effective cleaning practices into their designs. 

Similarly, NFPA 99 (Health Care Facilities Code) and NFPA 99B (Standard for Hypobaric Facilities) regulate the construction, operation, and maintenance of hyper- and hypobaric chambers with a focus on fire mitigation and protection.These regulations include the types of electrical equipment and wiring systems that can be used during construction as well as electrical and electronic equipment that is allowed inside a hyper- or hypobaric chamber during oxygen threapy.

A significant addition to the 2024 edition of NFPA 99 provides additional guidance for hyperbaric chamber operators and saftey directors related to the types of personal electrical and electronic equipment that are permitted inside a monopod-type (single patient) hyperbaric chamber. This additional guidance, with the approval of the hyperbaric medical director or saftey coordinator, allows equipment that conforms to one of the following conditions:

• Is intrinsically safe
• Is compliant with Class 1 requirements of NFPA 70 (National Electrical Code) Article 500
• Has batteries or circuitry sealed in such a way that they are isolated from the oxygen-enriched environment, has a maximum voltage and power requirement of 3V and 4W, and does not contain any volatile lubricants or solvents

Oxygen risk assessments can help healthcare providers identify and control potential fire safety issues.

Design practices for reducing fire risks

Manufacturers can also benefit from accounting for the following in their design practices to further inform mitigation strategies for fire risks in medical oxygen delivery systems. For medical facility operators, risk teams, and other potential stakeholders such as insurers, these practices are also valuable when evaluating potential fire risks and mitigation measures in settings where oxygen systems are used. Our expert teams help stakeholders understand and implement these practices to reduce the likelihood, consequence, and associated risk of an oxygen-enriched fire event. 

• Maximizing ignition-resistant materials: Designers can replace materials within their systems with alternatives that are more resistant to ignition (e.g., replace stainless steel with high nickel alloys, or select a gasket made from a material with a higher oxygen index). Maximizing the use of materials that are less susceptible to ignition helps mitigate potential fire risks.
• Minimizing the oxygen concentration and pressure: Higher oxygen concentrations and pressures mean more oxygen to support further fire growth. Designers can mitigate risks in their oxygen systems by avoiding unnecessarily high oxygen concentrations and pressures. Health professionals can employ a similar strategy when evaluating oxygen dosing rates and concentrations for patients by selecting settings that limit excess oxygen concentrations beyond the patient's medical needs. Other strategies healthcare providers can employ include using special draping procedures to avoid trapping oxygen under medical drapes and discontinuing the oxygen supply for a prescribed period before using a potential ignition source to allow the enriched oxygen atmosphere to dissipate.
• Following effective practices for ignition source control: Oxygen system designers recognize that many materials used in their systems can burn violently if exposed to a competent ignition source in an oxygen-enriched environment. Designers can employ effective practices — especially for cleaning — to eliminate factors like contamination that are known to contribute to ignition susceptibility of materials used in and around medical oxygen delivery systems. Contamination in oxygen systems, such as solid particulate matter or hydrocarbon residues, can compromise the fire safety of otherwise robustly designed systems. Oxygen safety experts frequently repeat the mantra "design clean, install clean, and maintain clean" as a well-known formula for fire risk control in oxygen system design. 

Industry-accepted practices for ignition source control can also apply to developing medical devices. Fire risk management can be woven into the design process, starting with identifying key product attributes and intended uses/environments that might present increased risk. As an example, ASTM's Technical Committee that oversees its oxygen standards (G04 Committee) has formed a task group to develop a new guide for performing oxygen compatibility assessments on oxygen components and systems. The guideline is influenced by NASA's Guide for Oxygen Compatibility Assessments, developed by NASA White Sands Test Facility personnel. Information from these types of assessments can then be translated into purposeful design engineering and labeling of the fire risks and key considerations for uses around medical oxygen use. Within the local environment, oxygen risk assessments can help healthcare providers identify and control potential fire safety issues in an effort to further mitigate the hazards associated with oxygen enrichment.