Hyperbaric Oxygen Test Facility
WHA has established a Hyperbaric Test Facility to gain a better understanding of chamber fire safety and to determine the oxygen compatibility of materials in hyperbaric oxygen (HBO). The test results provide HBO users with the necessary information and data to make educated decisions for safe material selection. WHA has four Seachrist 2500 series monoplace hyperbaric chambers which were generously donated by Diversified Clinical Services.
Compared to the number of HBO treatment facilities around the world, fires are an extremely rare event. Historically, the HBO community has been able to mitigate the risk of fire. However, most materials used in the construction of monoplace hyperbaric chambers and brought into these chambers during use are considered flammable at the most severe HBO conditions (i.e., highest pressure and oxygen concentration). These materials require a significant amount of energy for ignition to initially occur and ignition mechanisms are well controlled in HBO chambers since HBO fires are extremely rare. However, ignition mechanisms such as electrostatic discharge (ESD), exothermic reactions, frictional heating, electric arcing and electrical heating are always a concern in these chambers; yet, there is a lack of applicable data and guidance in the hyperbaric community to support an ignition risk analysis.
Although most non-metallic materials are flammable in hyperbaric conditions, these materials exhibit various rates of fire-propagation and amounts of energy release. A material that burns faster and with greater energy release provides less opportunity for 1) surrounding flammable materials to reject and dissipate heat energy and; 2) extinguishment measures to react and become effective. Based on the limited amount of existing fire-propagation and energy release data, there are significant differences between various materials. Certain materials need 100% oxygen to burn and will not burn in air or burn with significantly less energy in air. With this information quantified, monoplace hyperbaric chamber design and material selection would improve the ability to limit or extinguish a fire event. Such information would also be vital to studying effective fire suppression procedures and/or methods since propagation testing would allow fire-spread data to be collected and evaluated.
WHA, therefore, recommends the following testing options:
Autogenous Ignition Temperature
Consistent with the guidance of ASTM G63 Standard Guide for Evaluating Nonmetallic Materials for Oxygen Service, the typical method of evaluating material ignitability is performed by obtaining the material's autogenous ignition temperature (AIT). ASTM G72 Standard Test Method for Autogenous Ignition Temperature of Liquids and Solids in a High-Pressure Oxygen Enriched Environment is the standard test method for measuring the AIT in oxygen and was designed for high pressure oxygen (test pressure of 1500 psig). WHA has shown that the test cannot be simply modified to test at three atmospheres (43.5 psi) for hyperbaric conditions and still obtain repeatable and valid results. There is, therefore, a need to develop a new test standard to dependably obtain the AIT at three atmospheres of oxygen. This test could be located in a hyperbaric chamber, but it depends on the eventual design and procedure required for successful testing. Based on its interaction with the hyperbaric community, WHA believes this test is of the upmost priority and demand within the community.
Electrostatic discharge (ESD) is a possible ignition mechanism of concern in the HBO community. Although the fires associated with ESD seldom occur, and electrical grounding is commonly available, the risk remains poorly defined because of the lack of applicable experimental work. WHA has developed an ESD generator, consistent with standard human body models, that could be incorporated into a chamber simulating hyperbaric conditions. This would be used to determine the ignition energy of common materials found in hyperbaric chambers and then compare this energy to the potential ESD developed in chamber use. Small samples of materials such as clothing, bed sheets, and mattress covers could be exposed to ESD by the test system to determine the minimum spark ignition energy and establish whether these materials are at risk to the potential ESD in a HBO chamber.
New Component Ignition Risk Testing - Oxygen Exposure Testing
New products that have yet to be used in hyperbaric chambers such as exothermic creams, hand warmers, and other personal products that produce heat can be tested for HBO safety at WHA under worst case conditions. This would allow manufacturers to develop a good history of use and even consider testing single point mechanical/electrical failures before the devices are accepted for general hyperbaric use. Electrical components such as diagnostic tools, computers, audio devices and cell phones could also undergo a long-term oxygen exposure test in a controlled environment to ensure the product behaves safely in an HBO environment.