Oxygen Index

on . Posted in Chemical Engineering

Oxygen index, abbreviated as OI, is a measure of the flammability or combustibility of a material in the presence of oxygen.  It is used to assess the fire retardant properties of materials, particularly polymers and other substances.  The OI is expressed as a percentage and indicates the minimum concentration of oxygen in the air that is required to sustain combustion of a material.

The test for determining the OI involves placing a specimen of the material in a combustion chamber where the oxygen concentration can be controlled.  The material is then ignited at one end, and the concentration of oxygen is gradually decreased until the material stops burning.

The higher the oxygen index, the less likely the material is to support combustion.  Materials with high OI values are considered to have better fire resistance.  This index is particularly useful in assessing the fire safety characteristics of polymers and other materials used in various industries, including construction, electronics, and transportation.  Materials with high OI values are often preferred in applications where fire safety is a critical consideration.


Oxygen index Formula

\( OI =  ( O_c \;/\; O_n ) \;100 \)     (Oxygen Index)

\( O_c =   OI \; O_n \;/\; 100   \)

\( O_n =   OI \; 100 \;/\; OI   \)

Symbol English Metric
\( OI \) = oxygen index   \(dimensionless\)
\( O_c \) = oxygen concentration at which material sustains combustion \(ft^3 / sec\) \(m^3 / s\)
\( O_n \) = oxygen concentration in normal air \(ft^3 / sec\) \(m^3 / s\)


Oxygen Index

Oxygen index is an calculation of the flammability of plastics and other materials.

LOI = Limited Oxygen Index

Material LOI
Nomex 28.5
Nylon 6.6 24 - 29
Polymethyl Methacrylate (PMMA) 17.3
Phenolic 26 - 64
Plywood 23.0
Polycarbonate (PC) 25 - 44
Polyethylene (PE) 17.4
Polypropylene (PP) 17.4
Polystyrene (PS) 17.8
Polyester (GRP) 21- 43
Polytetrafluoroethylene (PTFE) 95
Polyvinyl Chloride (PVC) (unplasticised) 45 - 49
Std. Polyurethane (PU) foam 16.5


P D Logo 1

Tags: Air Tables Materials