An oxygen index test apparatus determines fire resistance by the minimum concentration of oxygen that can sustain combustion. The result of this measurement is called the Limiting Oxygen Index, which is expressed as a percentage. The higher the LOI value, the better the fire resistance of the material, since it requires a high oxygen environment to burn; hence, this test is a critical evaluation for safety-focused industries.
It works by exposing a vertically mounted material sample in a controlled oxygen-nitrogen atmosphere. A flame is presented to the material to ignite it, and the oxygen level is gradually changed. The observations that can be made are whether the material continues to burn for a specific time, usually three minutes, or burns through a specified length. For example, a material that has an LOI of 30% cannot burn in normal atmospheric conditions, with 21% oxygen, which offers greater safety in real life.
The testing process has very wide applications. In one case in 2021, an electronics manufacturer tested polymer casings and found that increasing LOI from 22% to 28% reduces ignition risks by 40%. The test results guided the company in the selection of flame-retardant materials, improving product safety and compliance with the standards laid down by UL 94.
“Safety doesn’t happen by accident” is a principle underlining the importance of correct fire resistance testing, in good congruence with the role of LOI measurements. Results of such are highly important in aerospace, automotive, and construction industries. For instance, one aerospace firm used LOI data to help certify cabin materials and, in the process, achieved a 25% reduction in fire spread during simulations and met FAA regulatory requirements.
The test apparatus also supports material innovation. A furniture manufacturer redesigned foam cushions after testing revealed vulnerabilities in fire resistance. By incorporating flame-retardant additives, the LOI increased from 20% to 32%, significantly enhancing the material’s safety profile.
The Oxygen Index Test Apparatus is a pivotal tool in the assessment and development of fire-resistant materials. Offering accurate and reproducible results, it underpins the development of safer designs and regulatory compliance, improving consumer confidence in a wide range of products.