System Level Analysis

ASTM G88 is a standard guide for the design of oxygen systems. This standard addresses system-level factors that affect the ignition and propagation of fire. Oxygen fires require the presence of an oxidizer (oxygen), a fuel (system materials or contamination), and a credible source of ignition (heat generating mechanism). WHA's system-level analyses using ASTM G88 focus on quickly identifying the most severe areas of a given system by considering system layout, the compatibility of materials of construction, and operational procedures, all of which can contribute to potential ignition and fire

Applying ASTM G88 on a system level requires three important steps, each of which functions to identify system-level hazards. Step 1 is to obtain system drawings or flow schematics that show oxygen flow from source to end-use and to list all system components. Included in this first step is the compilation of information from each component, including identification numbers, vendor information, and material specifications, if available.

Step 2 is to evaluate the severity of each component by considering three critical ASTM G88 factors as criteria for developing the Component Severity Ranking: material flammability, particle impact/adiabatic compression ignition, and personnel exposure. The factors are expressed as the following questions:

  1. Are the body and trim materials in the component considered flammable at the worst-case operating conditions? (Y/N) If all materials for a given component are NOT known, answer YES to this question.
  2. Does this component function as a throttling device (i.e. reducing pressure and/or controlling flow) OR does this component have a fast-opening characteristic (capable of pressurizing a downstream segment in less than a second, i.e. ball valves, globe valves, gate valves, etc.) (Y/N)
  3. Is this component manually operated OR are personnel within close reach of this component when it's being operated? (Y/N)

To answer Question 1, metals flammability test data is referenced. For metals; data per Standard Test Method for Determining the Combustion Behavior of Metallic Materials in Oxygen-Enriched Atmospheres (ASTM G124). For nonmetals, oxygen index data is referenced per the Standard Test Method for Measuring the Minimum Oxygen Concentration to Support Candle-Like Combustion of Plastics (Oxygen Index, ASTM D2863).

To answer Question 2, WHA considers the component's function and operation as well as its location in the system relevant to other components. Finally, to answer Question 3, the component's operation and associated system conditions are considered in context with the potential for personnel exposure to a fire.

Step 3 of the system level assessment uses the answers to the above three questions to rank the severity of components. This analysis is designed to inventory the system and quickly identify and rank the "severe" components, those at greatest risk to ignition and fire propagation, and hazardous to personnel. The severe components are then required to undergo a Component Level Assessment.

Download WHA's System-level worksheet

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