What Is ASTM G175 and Why Does It Matter for Oxygen Filters?

A filter that passes standard oxygen compatibility testing can still become the ignition point for a catastrophic system fire. Standard tests measure whether materials ignite under normal pressurization, but they cannot predict how a component responds when something goes wrong.

ASTM G175 Phase 2 solves this problem by simulating an active fire upstream of the filter and measuring whether the component contains the ignition event or breaches and propagates the fire downstream. For design engineers specifying oxygen filtration in aerospace, medical and industrial gas systems, this standard determines whether a filter protects critical equipment or accelerates failure.

What Is ASTM G175?

ASTM G175 is a standard test that ASTM International’s Committee G04 developed for medical oxygen pressure regulators. Engineers have since adapted the Phase 2 methodology to other oxygen service components, particularly filters, because it evaluates fault tolerance rather than basic compatibility.

The standard includes two distinct phases that measure different failure modes. Understanding what each phase tests helps engineers specify components that won’t contribute to system fires when operating conditions deteriorate.

Phase 1: The Oxygen Pressure Shock Test

The Phase 1 test subjects the filter to rapid high-pressure oxygen delivery to determine whether adiabatic compression alone triggers ignition or heat damage. This baseline oxygen filter testing phase assesses how easily realistic pressurization conditions cause a fire. It measures ignition sensitivity under the thermal conditions that rapid valve opening or pressure surges create in operational systems.

Components that pass Phase 1 demonstrate that they resist self-ignition during normal system dynamics. This phase cannot predict how the filter responds when contamination or mechanical failure introduces an ignition source.

Phase 2: The Promoted Ignition Test

Phase 2 evaluates what happens after something goes wrong. An ignition pill detonates upstream of the filter to simulate an active fire in the system. This promoted ignition methodology tests the filter’s fault tolerance in this active fire scenario. It measures the filter’s ability to contain the ignition event without breaching its body, expelling hazardous molten material downstream, or allowing the fire to propagate further into the system.

Engineers who specify filters for safety-critical applications need this data to ensure the filter protects downstream piping and components when an ignition event occurs.

The Unique Challenges of High-Pressure Oxygen Service

Oxygen service filtration operates under different rules than air or inert gas systems. The elevated concentration of oxygen lowers the ignition temperature of surrounding materials, turning the system’s own components into potential fuel. Piping, seals and filter elements that remain inert in air service can become combustible in high-pressure oxygen environments. Oxygen’s reactivity turns any heat-releasing mechanism into a potential ignition source.

The NFPA identifies three elements required for fire, including combustible material, an ignition source and oxygen. High-pressure oxygen systems concentrate the oxidizer to such extreme levels that separating these three elements becomes nearly impossible, so engineers must design components that remain fault-tolerant even when ignition occurs.

Ignition Mechanisms in Oxygen Systems

Filters face multiple ignition risks simultaneously:

• Adiabatic compression: Rapid pressure changes across the filter generate significant heat, which can ignite susceptible materials within the system.
• Particle impact: High-velocity contaminants striking internal surfaces create localized hot spots, serving as potent ignition points.
• Friction: Moving parts in contact within the filter assembly can generate sufficient thermal energy to reach ignition temperatures.
• Mechanical impact: Component failures or the sudden impact of debris can produce an energetic spark or heat release capable of triggering an ignition event.

Filters sit at the convergence of all these risks. They constantly capture particles that represent ignition hazards themselves, and they create the exact pressure drop conditions where adiabatic heating occurs. A filter that designers do not engineer and test for oxygen service can become the ignition point rather than the protection mechanism.

Why Material Selection Matters

Material choice determines whether a filter contains an ignition event or fails catastrophically when fire reaches the component. Research on promoted ignition testing shows that brass outperforms other materials in fault-tolerance applications. Stainless steel offers superior mechanical strength, but promoted combustion testing data demonstrates that it sustains burning, which can breach the filter body and eject molten debris.

Compare the following materials and their fire resistance:

• Aluminum supports combustion at approximately 25 PSI.
• Stainless steel sustains burning up to 500 PSI.
• Brass and bronze resist sustained combustion up to 10,000 PSI.

The difference in combustion resistance translates directly to fault tolerance. Brass construction contains fire within the filter body rather than allowing it to propagate through breaches or ejected material. Therefore, brass is an ideal material for oxygen-compatible filters to protect downstream equipment.

Why This Standard Is Critical for Many Industries

Multiple industries require defensible component qualification for oxygen service because system fires carry catastrophic consequences.

• Medical: Delivery systems fall under U.S. Food and Drug Administration scrutiny. The agency applies similar safety expectations to downstream filters based on the rigorous standards set for regulators.
• Industrial: Oxygen plants, cylinder filling stations and pipeline systems with continuous high-pressure flow demand components that operators can defend with third-party test data.
• Aerospace and military: In environments where system fires threaten lives, missions and equipment, the use of components with fully documented and traceable testing becomes mandatory.
• Energy and chemicals: Facilities using oxygen-enhanced combustion, bleaching or oxidation require filters that can simultaneously resist ignition while protecting other critical equipment from contamination.

The Difference Between Oxygen Cleaned and Fault-Tolerant Filters

An oxygen-cleaned filter does not equal an oxygen-tested filter. For safety-critical systems where engineers must prepare for worst-case scenarios, ASTM G175 Phase 2 testing is the only way to prove a filter will not turn into additional fuel when an ignition event occurs. While oxygen cleaning is a critical first step, requiring fault-tolerance testing allows engineers to enhance system integrity and verifiably guard equipment against chain-reaction failures.

Specifications Checklist for Oxygen Filters

When specifying industrial oxygen filters, remember these checks:

1. Demand test documentation: Insist on seeing the third-party ASTM G175 Phase 2 test report. This is the only way to verify a component is fault-tolerant and prepared for a worst-case ignition scenario.
2. Verify the material: Confirm the component is made from brass or another material with empirically proven fault tolerance.
3. Confirm oxygen cleaning: Ensure the component has documentation proving it was assembled in an oxygen-clean environment per standards like CGA G-4.1 to eliminate initial ignition risks from contaminants.
4. Require full traceability: For high-stakes applications such as aerospace and military, ensure complete component traceability to guarantee material provenance and quality control, where failure is not an option.

Setting the Standard for Oxygen Filters at Chase Filters & Components

Chase Filters & Components first developed high-pressure oxygen filters for U.S. Navy applications. Over the past three decades, we’ve built on that engineering foundation to serve aerospace, medical and industrial gas markets. Our brass oxygen filter lines completed Phase 2 testing by Wendell Hull International, proving these filters contain ignition events to protect your downstream equipment.

Contact our engineering team today to discuss your filtration requirements.