The limiting oxygen index (LOI) is the most quoted single number in polymer flammability: the minimum percentage of oxygen in an oxygen-nitrogen mixture that will just support combustion of a small vertical specimen. Higher LOI means a material is harder to keep burning. Motis builds the test in two forms: the COI with an imported paramagnetic oxygen sensor and digital gas-flow display, and the fully automatic AOI, including high-temperature versions for ISO 4589-3 elevated-temperature testing.
How the Oxygen Index Tester (LOI) works
A small bar or film specimen is mounted vertically in a glass chimney. A controlled mixture of oxygen and nitrogen flows upward; the specimen is ignited at the top and the oxygen concentration is adjusted until the burning criterion of the standard is just met. That concentration is the oxygen index. The COI reads the mixed-gas oxygen percentage directly from its paramagnetic sensor, with no manual calculation from flow readings.
Key specifications
| Standards | ISO 4589-2, ISO 4589-3 (elevated temperature, AOI), ASTM D2863, GB/T 2406 |
|---|---|
| Oxygen sensor | Imported paramagnetic sensor, accuracy better than 0.1% (COI) |
| Display | Digital display of nitrogen flow, mixed-gas flow and oxygen concentration percentage; no manual calculation |
| Chimney | High-temperature resistant quartz glass tube |
| Ignition | Gas ignition device with adjustable flame length and gas cut-off |
| Specimen holders | Clamps for self-supporting and non-self-supporting specimens |
| Models | COI (paramagnetic), AOI (fully automatic), plus OI/LOI variants by configuration |
What the test reports
- Limiting oxygen index (oxygen concentration, %)
- Burning behaviour observations required by the standard
Applications
LOI is used across cable compounds, engineering plastics, textiles, foams and coatings for formulation screening and incoming-material control. It is a comparative small-scale test: use it to rank materials and to control consistency, and use the bench-scale instruments for classification evidence.
Frequently asked questions
Which standard should I order against?
Order against the standard your reports must cite. The instrument platform is shared across the listed standards, but fixtures, software templates and calibration routines differ, so name the standard (and its year) in your inquiry and the configuration will be matched to it.
COI or AOI - which should I choose?
Choose the AOI if you run the test at volume or need elevated-temperature testing to ISO 4589-3, since the automatic model controls the gas adjustment for you. The COI suits laboratories that run the test regularly but want direct digital readout with manual control.
What does an LOI value tell me about real fire behaviour?
It tells you how readily a small specimen keeps burning in a controlled oxygen mixture - a material property, not a prediction of a full-scale fire. Standards bodies use it for specification and quality purposes, not as a classification test on its own.
Configuration, installation and support
Every Oxygen Index Tester (LOI) is supplied as a configured system, not a bare instrument: the test chamber or frame, the burner or heater assemblies named in the method, the measurement chain and the control software with the report templates for ISO 4589-2, ISO 4589-3, ASTM D2863, GB/T 2406. Before quotation we confirm the installation conditions with you - floor loading and ceiling height for large rigs, exhaust and extraction routes, gas and fuel services, and power supply - because a fire test instrument only produces defensible data when the room around it is right. Commissioning covers assembly, calibration of the measurement chain against the method's own checks, and training of your operators on running the test and maintaining the apparatus. Spare ignition parts, thermocouples and other consumables for the first period of operation can be included in the supply, and the instrument is supported with calibration and maintenance services after installation.
What to include in your inquiry
To quote the Oxygen Index Tester (LOI) correctly the first time, send: the standard and edition you will test to (ISO 4589-2, ISO 4589-3, ASTM D2863, GB/T 2406); the materials or products you will test and their sizes; the configuration options you already know you need; and the destination laboratory's location and available services. If you are building a new fire laboratory rather than adding one instrument, say so - this apparatus is often planned together with the other instruments in its category, and a combined layout and exhaust plan is cheaper than three separate ones.