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Understanding CAN/CGSB 4.2 No. 73.5-M91 (2013): Textile Flame Spread Test Method
Comprehensive Guide to the 45° Angle Flame Spread Test for Textile Fabrics
Scope and Application
The CAN/CGSB 4.2 No. 73.5-M91 (2013) standard is part of the Canadian General Standards Board (CGSB) 4.2 series of textile test methods. Specifically, it describes a procedure for determining the flame spread time of textile fabrics using a 45° angle test apparatus. This method is applied to evaluate the flammability of apparel textiles, upholstery fabrics, and certain household textiles when subjected to a small, open flame.
The test measures the time required for a flame to travel a specified distance along the surface of a fabric specimen mounted at an angle of 45°. It is intended for use in quality control, product certification, and regulatory compliance within Canada. The method is applicable to woven, knitted, and nonwoven fabrics, as well as coated or laminated textiles, provided they can be cut to the required specimen dimensions.
Tip: This test is often referenced alongside other flammability methods such as CAN/CGSB 4.2 No. 73.1 (vertical flame test) and No. 73.2 (hose test). The 45° test is especially relevant for garments and curtains where flame spread along a sloping surface is a realistic fire scenario.
Technical Requirements
Test Apparatus
The standard specifies a test chamber equipped with a specimen holder that maintains the fabric at a 45° angle. A standardized ignition source, typically a small butane or methane flame of defined length (e.g., 16 mm), is applied to the lower edge of the specimen. A suitable timing device (stopwatch or automatic timer) is used to record flame spread over a gauge line located 125 mm from the point of ignition.
Specimen Preparation and Conditioning
Each test specimen is cut to dimensions of 150 mm × 75 mm. A total of five specimens are tested in the warp (lengthwise) direction and five in the weft (crosswise) direction. Before testing, specimens are conditioned at 20 °C ± 2 °C and 65 % ± 5 % relative humidity for at least 24 hours. This conditioning ensures reproducible moisture content, which can significantly influence flammability results.
Test Procedure
The specimen is mounted in the holder with the side to be exposed facing upward. The flame is applied for a specified time—usually 1 second—and then removed. The timer starts when the flame touches the fabric. The end point is defined as the moment the flame front reaches the gauge line. If the specimen does not ignite, fails to propagate flame to the gauge line, or self-extinguishes before reaching the line, the result is recorded as “no ignition” or “not applicable.”
The standard sets forth a pass/fail criterion: the average flame spread time for each direction must exceed a specified minimum value. For most apparel fabrics, the minimum average flame spread time is 3.5 seconds when tested by this method. Materials that burn faster than this threshold may be considered flammable and require special labelling or construction restrictions.
Parameter Requirement Specimen size 150 mm × 75 mm (± 1 mm) Number of specimens per direction 5 (warp), 5 (weft) Conditioning atmosphere 20 °C ± 2 °C, 65 % ± 5 % RH, ≥ 24 h Flame height 16 mm ± 1 mm (measured from nozzle) Ignition time 1.0 s ± 0.2 s Angle of specimen 45° from horizontal Gauge line distance 125 mm from ignition point Pass criterion (average per direction) ≥ 3.5 seconds flame spread time
Implementation Highlights
Laboratories implementing this standard must ensure that the test chamber and specimen holder are constructed according to the detailed drawings provided in the standard. The burner assembly must allow consistent gas flow, and a pressure gauge or regulator is recommended to maintain flame height reproducibility.
One crucial practical aspect is the interpretation of the flame front. The standard requires visual observation of the leading edge of the flame. For fabrics that exhibit melting or shrinkage before ignition, the operator must take care to distinguish between true flame propagation and melting behavior. In such cases, the fabric may need to be tested with a seam or edge treatment to simulate end-use performance.
Warning: Surface-textured fabrics (e.g., napped, brushed, fleece) often show rapid flame spread due to increased surface area. Test results for such materials should be interpreted with caution, and additional testing according to other methods may be required for regulatory approval.
Comparison with Other Standards
The CAN/CGSB 4.2 No. 73.5 test shares similarities with ASTM D1230 (Standard Test Method for Flammability of Apparel Textiles) but differs in specimen dimensions, conditioning requirements, and pass/fail limits. While ASTM D1230 uses a 150 mm × 50 mm specimen and a 45° angle, the Canadian standard requires a wider specimen (75 mm) and a different distance to the gauge line. Consequently, results are not directly interchangeable, and the correct standard must be cited in any Canadian compliance documentation.
Compliance and Regulatory Notes
This standard is referenced in several Canadian regulations, including:
- Hazardous Products Act – for flammability requirements of textile products (e.g., children’s sleepwear, camping tents).
- Canada Consumer Product Safety Act – for general apparel and upholstery.
- Transport Canada – for interior materials in public transportation vehicles.
Manufacturers and importers must ensure that their textile products meet the applicable flame spread limits when tested by a laboratory accredited to this method. The standard itself is a reaffirmation of the 1991 edition, meaning the technical requirements have not changed; only minor editorial corrections and updates to referenced documents are included in the 2013 reaffirmation.
Compliance Tip: Always verify the latest revision status of referenced standards (e.g., CAN/CGSB 4.2 No. 41.2 for conditioning) to ensure your testing regime is up to date.
Non-compliance can result in product recalls, fines, or restrictions on sale. It is advisable to maintain a documented testing schedule, retain records of all test results, and review any changes in the standard through the CGSB website or authorized distributors.
Important: This standard is part of a withdrawal process in favor of harmonized methods (e.g., ISO 6940/6941). Check with regulatory authorities before committing to long-term use of the 73.5 method for certification.
Frequently Asked Questions
Q: What is the main difference between CAN/CGSB 4.2 No. 73.5-M91 (2013) and the vertical flame test (No. 73.1)?
A: The primary difference is specimen orientation. No. 73.5 uses a 45° incline, which simulates flame spread on a garment worn by a standing person. The vertical test (No. 73.1) is more severe and is typically used for protective clothing and curtains. The pass/fail criteria also differ, with No. 73.5 requiring a minimum average spread time of 3.5 seconds, while No. 73.1 normally requires a maximum char length or after-flame time.
A: The primary difference is specimen orientation. No. 73.5 uses a 45° incline, which simulates flame spread on a garment worn by a standing person. The vertical test (No. 73.1) is more severe and is typically used for protective clothing and curtains. The pass/fail criteria also differ, with No. 73.5 requiring a minimum average spread time of 3.5 seconds, while No. 73.1 normally requires a maximum char length or after-flame time.
Q: Can I use CAN/CGSB 4.2 No. 73.5‑M91 for testing non‑woven fabrics?
A: Yes, the standard is applicable to non‑woven fabrics provided they can be cut to the specified size and do not melt or shrink away from the flame before ignition. If the fabric exhibits excessive melting, the test may not be valid, and alternative methods (e.g., ASTM D6413) should be considered.
A: Yes, the standard is applicable to non‑woven fabrics provided they can be cut to the specified size and do not melt or shrink away from the flame before ignition. If the fabric exhibits excessive melting, the test may not be valid, and alternative methods (e.g., ASTM D6413) should be considered.
Q: Does this standard require a specific number of specimens for each direction?
A: Yes, five specimens are required in the warp direction and five in the weft direction, for a total of ten tests per sample. If the fabric is non‑directional (e.g., knitted tubes), ten specimens are taken from representative areas.
A: Yes, five specimens are required in the warp direction and five in the weft direction, for a total of ten tests per sample. If the fabric is non‑directional (e.g., knitted tubes), ten specimens are taken from representative areas.
Q: How often is the standard updated?
A: The original edition was published in 1991, and it was reaffirmed in 2013. Reaffirmations typically occur every five to ten years. Users should monitor the CGSB website for announcements of future revisions or withdrawals.
A: The original edition was published in 1991, and it was reaffirmed in 2013. Reaffirmations typically occur every five to ten years. Users should monitor the CGSB website for announcements of future revisions or withdrawals.
This article provides general guidance on the CAN/CGSB 4.2 No. 73.5‑M91 (2013) standard. Always refer to the official standard document for complete and authoritative requirements. Last updated: 2026.