Gwenael J. A. Chiffoleau

Adiabatic Compression Testing—Part II: Background and Approach to Estimating Severity of Test Methodology

Adiabatic compression testing of components in gaseous oxygen is a test method that is utilized worldwide and is commonly required to qualify a component for ignition tolerance under its intended service. This testing is required by many industry standards organizations and government agencies; however, a thorough evaluation of the test parameters and test system influences on the thermal energy produced during the test has not yet been performed. This paper presents a background for adiabatic compression testing and discusses an approach to estimating potential differences in the thermal profiles produced by different test laboratories. A “Thermal Profile Test Fixture” (TPTF) is described that is capable of measuring and characterizing the thermal energy for a typical pressure shock by any test system. The test systems at Wendell Hull & Associates, Inc. (WHA) in the USA and at the BAM Federal Institute for Materials Research and Testing in Germany are compared in this manner and some of the data obtained is presented. The paper also introduces a new way of comparing the test method to idealized processes to perform system-by-system comparisons. Thus, the paper introduces an “Idealized Severity Index” (ISI) of the thermal energy to characterize a rapid pressure surge. From the TPTF data a “Test Severity Index” (TSI) can also be calculated so that the thermal energies developed by different test systems can be compared to each other and to the ISI for the equivalent isentropic process. Finally, a “Service Severity Index” (SSI) is introduced to characterizing the thermal energy of actual service conditions. This paper is the second in a series of publications planned on the subject of adiabatic compression testing.

Reflection of structural waves at a solid/liquid interface

This paper investigates the reflection characteristics of structural or guided waves in rods at a solid/liquid interface. Structural waves, whose wavelengths are much larger than the diameter of the rod, are described in a first approximation by classical one-dimensional wave theory. The reflection characteristics of such waves at a solid/liquid (melting) interface has been reported by two different ultrasonic measurement techniques: first, measuring the fast regression rate of a melting interface during the burning of metal rod samples in an oxygen-enriched environment, and second, monitoring the propagation of the solid/liquid interface during the slow melting and solidification of a rod sample in a furnace. The second work clearly shows that the major reflection occurs from the solid/liquid interface and not the liquid/gas interface as predicted by plane longitudinal wave reflectivity theory. The present work confirms this observation by reporting on the results of some specially designed experiments to identify the main interface of reflection for structural waves in rods. Hence, it helps in explaining the fundamental discrepancy between the reflection characteristics at a solid/liquid interface between low frequency structural waves and high frequency bulk waves, and confirms that the detected echo within a burning metallic rod clearly represents a reflection from the solid/liquid interface.

The selection of skin care products for use in hyperbaric chamber may depend on flammability acceptability indices score

PURPOSE: Current protocols call for stopping adjunctive skin care treatments during hyperbaric oxygen therapy (HBOT) because the hyperbaric environment is considered unsafe for skin care products. The elevated oxygen fraction and the increased pressure in the hyperbaric chamber dramatically increase the flammability potential of materials, leading to the need for rigorous standards to prevent flame ignition. A scientific method of evaluating the flammability risks associated with skin care products would be helpful. Several skin care products were tested, using established industrial techniques for determining flammability potential with some modification. The information obtained from these tests can help clinicians make more rational decisions about which topical products can be used safely on patients undergoing HBOT. METHODS AND MATERIALS: Wendell Hull & Associates conducted independent studies, comparing the oxygen compatibility for leading skin care products. Oxygen compatibility was determined using autogenous ignition temperature (AIT), oxygen index (OI), and heat of combustion (HoC) testing. AIT, a relative indication of a materials propensity for ignition, is the minimum temperature needed to cause a sample to self-ignite at a given pressure and oxygen concentration. OI, a relative indication of a materials flammability, is the minimum oxygen percentage that, when mixed with nitrogen, will sustain burning. HoC is the absolute value of a materials energy release when burning, if ignition occurs. Products with a high AIT, a high OI, and a low HoC are more compatible in an oxygen-enriched atmosphere (OEA). An acceptability index (AI) based on these 3 factors was calculated for the products, so the testers could rank overall material compatibility in OEAs (Lapin A. Oxygen Compatibility of Materials. International Institute of Refrigeration Commission Meeting; Brighton, England; 1973). RESULTS: Test results for the skin products varied widely. The AIT, OI, HoC, and AI were determined for each product under described circumstances. The AIT results indicate that all products in 99.5% oxygen concentration under pressure will ignite and that a pattern based on the absence or presence of petroleum-based ingredients does not seem to exist. Products containing petrolatum, mineral oil, paraffin, and paraffin wax had a HoC that equaled or exceeded the HoC of gasoline, whereas products without petroleum-based ingredients had a significantly lower HoC. The OI of skin products not containing petrolateum-based ingredients was significantly higher than the OI of products containing it. The AI values the OI as the most important value: the higher the AI, the more acceptable the product is for use with oxygen. The silicone-containing, petroleum-free products received an AI up to 25 times higher than the petrolatum-based products. These findings suggest a wide variation in the safety profiles of skin products. Skin products being considered for use in an OEA should be screened for flammability risks. This screening will allow informed decisions about the fire safety of the products. Further research is indicated.

Determination of the Regression Rate of a Fast Moving Solid/Liquid Interface Using Ultrasonics

This paper reports on an ultrasonic measurement system and its application for in situ real-time measurement of very fast regression rates (>200 mm/s) of the melting interface (RRMI) produced when burning particular metals such as aluminium at high pressures. The RRMI is referred to as the rate at which a solid/liquid interface moves along a metallic rod while burning in an oxygen-enriched atmosphere. The ultrasonic transducer and associated equipment used to drive and record the transducers output signal and conversion of this output into a regression rate is described. Aluminium rods were burned in pure gaseous oxygen at pressures up to 69 MPa (10,000 psia) where the RRMI was calculated at 204+/-2 mm/s. Other tests with a variety of sample materials, geometric shapes and test conditions were also conducted. The resulting RRMIs calculated with the ultrasonic measurement system compare excellently with rates obtained using a visual review of the same tests and with published results (where available).

An Approach to Understanding Flow Friction Ignition: A Computational Fluid Dynamics (CFD) Study on Temperature Development of High-Pressure Oxygen Flow Inside Micron-Scale Seal Cracks

Flow friction ignition of non-metallic materials in oxygen is a poorly understood heat- generating mechanism thought to be caused by oxygen flow past a non-metallic sealing surface. Micron- scale fatigue cracks or channels were observed on non-metallic sealing surfaces of oxygen components and could provide a leak path for the high-pressure oxygen to flow across the seal. Literature in the field of micro-fluidics research has noted that viscous dissipation, a heat-generating mechanism, may not be negligible as the flow dimension of the channel is reduced to the micron-scale. Results of a computational fluid dynamics study are presented and used to determine if temperatures developed in high-pressure driven micro-channel oxygen flows are capable of reaching the reported autogenous ignition temperature of non-metallic materials in oxygen.

Instantaneous RRMI of iron rods in reduced gravity

Standard upward-burning promoted ignition tests (“Standard Test Method for Determining the Combustion Behavior of Metallic Materials in Oxygen-Enriched Atmospheres,” ASTM G4-124 [1] or “Flammability, Odor, Offgassing, and Compatibility Requirements and Test Procedures for Materials in Environments that Support Combustion,” NASA-STD-6001, NASA Test 17 [2]) were performed on cylindrical iron (99.95% pure) rods in various oxygen purities (95.0–99.98%) in reduced gravity onboard NASA JSCs KC-135 to investigate the effect of gravity on the regression rate of the melting interface. Visual analysis of experiments agrees with previous published observations showing distinct motions of the molten mass attached to the solid rod during testing. Using an ultrasonic technique to record the real-time rod length, comparison of the instantaneous regression rate of the melting interface and visual recording shows a non-steady-state regression rate of the melting interface for the duration of a test. Precessional motion is associated with a higher regression rate of the melting interface than for test periods in which the molten mass does not show lateral motion. The transition between the two types of molten mass motion during a test was accompanied by a reduced regression rate of the melting interface, approximately 15–50% of the average regression rate of the melting interface for the entire test.

Promoted Ignition Testing of Metallic Filters in High-Pressure Oxygen

Currently, no test standard exists for evaluating the ignition tolerance and fault tolerance of metallic filters in high-pressure oxygen. Filters are a critical component in oxygen systems to ensure system cleanliness and mitigate ignitions by particle impact and contamination. However, filters are at risk to these same ignition mechanisms and fires have occurred in service. A new test method was developed using ASTM Standard G175 Phase 2 as a basis. The test subjects a pre-contaminated filter to a forced ignition event using an ignition pill while the filter is maintained at elevated pressure. Prior to testing, contaminant was applied to the filter element and was also placed at the filter inlet. This additional contaminant was based on contaminant that could potentially accumulate in a filter over time. This contaminant consisted of aluminum powder, iron particles, and perfluorinated lubricant. An ignition pill, consistent with ASTM Standard G175 Phase 2, was located on the upstream side of the filter. A back pressure was applied downstream of the ignition pill to ensure that the filter was pressurized during the ignition and burning of the pill. Testing was performed on brass and stainless steel filters of the same design using an oxygen shock to ignite the ignition pill at a test pressure greater than the back pressure applied to the filter. The brass filters safely contained the ignition event without breaching through the filter element or body. For the stainless steel filters, the ignition event kindled the filter element and burned through the filter body. This testing showed that the ignition fault tolerance of the brass filters was far superior to that of the stainless steel filters, which was consistent with the relative flammability of these metallic materials, and therefore verified the test methodology.

Analysis Tools Used to Evaluate Oxygen Hazards and the Oxygen Compatibility of Metals

Performing analyses of the fire hazards in oxygen systems is critical to avoiding fires. Over the years, several systematic approaches to analyzing fire hazards in oxygen systems have been proposed and analysis methodologies for oxygen systems have become more refined. Specific evaluation is performed on the compatibility of materials of construction, the presence of ignition mechanisms, and the effects that ignition or a fire would have on the component, system, and personnel. The authors of this paper routinely perform hazards analyses and failure analyses of oxygen systems for their clients and have applied new engineering technologies and materials test data to better understand, discern, and characterize oxygen fire hazards. This paper describes some of the new technologies and materials test data used and how they can be applied to evaluating the compatibility of metals in oxygen service, including three-dimensional component analysis; Computational Fluid Dynamics (CFD) flow modeling; metals flammability test data in static, flowing, and high-temperature oxygen; and metals ignition test data.

Ultrasonic Measurement Technique of Burning Metals in Normal and Reduced Gravity

The in situ real time measurement of the regression rate of a melting interface (RRMI) is performed by the ultrasonic measurement system reported here. The RRMI is the rate at which a solid/liquid interface (SLI) moves along a metallic rod while burning in an oxygen-enriched atmosphere and is an important flatnmability indicator. The ultrasonic transducer and associated equipment used to drive the transducer and record the echo signal is described, along with the process that transforms the acquired signals into a RRMI value. Test rods of various metals and geometric shapes were burned at several test conditions in different test facilities. The RRMI results with quantified errors are presented and reviewed. The effect of reduced gravity on burning metals is important to space-applications and RRMI results obtained in a reduced gravity environment are also presented.

Oxygen Fire Hazards in Valve-Integrated Pressure Regulators for Medical Oxygen

In recent years, medical oxygen regulators that incorporate a cylinder isolation valve have increased in popularity. These devices, often called valve-integrated pressure regulators (VIPRs), essentially combine several components into one highly compact manifold design, typically including a fill valve, shut-off valve, residual pressure valve, regulator, and relief valve. Combining these components into a single manifold block presents unique oxygen fire hazards that can differ greatly from those found in the stand-alone versions of the components. In order to avoid fires, these hazards must be understood and addressed in the design of the VIPR. This paper presents the most common oxygen fire hazards found in VIPR devices as well as the ASTM analysis and testing methods used to qualify a new design, specifically considering oxygen compatibility of materials, toxicity of combustion products, ignition mechanisms, and reaction effects of a fire.