ASTM D2863 Limiting Oxygen Index (LOI) Testing for Plastics & Textiles
ASTM D2863 is a test method for measurement of the minimum concentration of oxygen, in an oxygen-nitrogen mixture present in a plastic sample, that supports Candle-like Plastic combustion (oxygen index).
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- Overview
- Scope, Applications, and Benefits
- Test Process
- Specifications
- Instrumentation
- Results and Deliverables
Overview
ASTM D2863 defines a standardised method for measuring the minimum concentration of oxygen in an oxygen-nitrogen mixture that will support flaming combustion of a plastic material — a value known as the Limiting Oxygen Index (LOI) or Oxygen Index (OI). Since normal air contains approximately 21% oxygen, materials with an LOI above 21% are considered self-extinguishing in air, while those below 21% will sustain burning.
The test involves supporting a specimen vertically in a transparent glass chimney, igniting the top of the specimen, and then flowing a controlled mixture of oxygen and nitrogen upward through the chimney. The oxygen concentration is systematically adjusted until the minimum concentration that just supports combustion for a specified duration or burn length is identified. This value directly reflects the inherent flammability behaviour of the material.
Scope, Applications, and Benefits
Scope
ASTM D2863 evaluates:
- Limiting oxygen index (LOI) of plastic materials
- Minimum oxygen concentration for sustained combustion
- Effect of flame retardant additives on LOI
- Comparative flammability ranking of polymers
- Influence of specimen orientation on burning behavior
- Effect of thickness on oxygen index values
Applications
- Flame retardant polymer formulation development
- Electrical and electronic enclosure materials
- Building and construction plastic components
- Transportation interior materials (aviation, rail)
- Wire and cable insulation qualification
- Textile and fibre flame retardancy evaluation
- Research and development in fire science
Benefits
- Provides a precise numerical flammability index
- Enables rapid screening of flame retardant effectiveness
- Supports comparative ranking of polymer flammability
- Guides flame-retardant additive selection and loading
- Provides data for fire safety material approvals
- Applicable to a wide range of polymer types
Test Process
Specimen Preparation
Specimens are cut or molded to the standard geometry and conditioned.
1Gas Flow Setup
Oxygen and nitrogen flow rates are set to achieve the target oxygen concentration.
2Ignition
The top surface of the specimen is ignited with the standard igniter.
3Concentration Adjustment
Oxygen concentration is incrementally adjusted to find the minimum value supporting sustained burning.
4Technical Specifications
| Parameter | Details |
|---|---|
| Specimen Orientation | Vertical |
| Applicable Materials | Plastics, polymer sheets, films, laminated and cellular materials |
| Specimen Thickness | Up to 10.5 mm (self-supporting materials) |
| Test Environment | Controlled gas flow and ambient laboratory conditions |
| Specimen Types | Vertical bars, sheets, films, and flexible specimens |
Instrumentation Used for Testing
- Oxygen index test column (glass chimney)
- Precision oxygen and nitrogen gas flow controllers
- Oxygen analyser / concentration monitor
- Specimen holder and ignition torch
- Stopwatch/timer
- Data recording system
Results and Deliverables
- Limiting oxygen index (LOI) value
- Combustion behavior observations
- Effect of flame retardant level on LOI (comparative)
- Specimen burn length and time data
- Flammability classification report
Frequently Asked Questions
It measures the minimum concentration of oxygen required to support continuous burning of a plastic specimen.
LOI stands for Limiting Oxygen Index, expressed as the percentage of oxygen in an oxygen–nitrogen mixture needed for sustained combustion.
A higher LOI value means better flame resistance and lower flammability.
Plastics, films, sheets, foams, laminates, and other polymer-based materials can be tested.
It is widely used in plastics, aerospace, automotive, cable insulation, electronics, and construction materials industries.
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