Any clothing textile sold in the United States has to meet the Standard for the Flammability of Clothing Textiles, 16 CFR Part 1610. The test itself takes seconds: a strip of fabric is held at 45°, a small butane flame touches it for one second, and a timer records how long the flame takes to travel up the specimen.
Because the burn is so short, the result is extremely sensitive to everything that happens before the flame. That is where most laboratories go wrong.
What the test actually measures
The regulation defines the apparatus and procedure in detail. The figures below come from the text of 16 CFR 1610 itself:
| Parameter | Requirement |
|---|---|
| Specimen | 50 mm × 150 mm |
| Angle | 45° |
| Flame | 16 mm, chemically pure butane |
| Flame impingement | 1 second |
| Stop thread | 127 mm from the point of impingement |
| Oven drying | 30 ± 2 min at 105 ± 3 °C |
| Desiccator | silica gel, not less than 15 min |
| Start of test | within 45 s of removal from the desiccator |
The burn time is the time from ignition until the flame burns the stop thread. Short burn times mean fast flame spread, which is the hazard the standard is written to catch.
Error 1: treating the drying step as optional
Many labs condition specimens to their normal textile atmosphere and test them as they are. The regulation does not do that. It dries the specimens in an oven, cools them over desiccant and then gives the operator 45 seconds to start the test.
A specimen that has re-absorbed moisture burns more slowly, so skipping or stretching this step makes fabrics look safer than they are. Put the desiccator next to the cabinet, not across the room, and time the transfer.
Error 2: brushing raised surfaces the wrong way
For raised-surface fabrics — fleece, velour, flannel, terry, chenille — the specimen is brushed once with the brushing device before testing. The carriage is drawn forward once by hand, against the lay of the fibres, with a brush pressing at a defined load.
Brushing with the lay, brushing twice or skipping it changes how the surface fibres stand and therefore how fast the surface flash travels. Raised fabrics are exactly where Class 2 and Class 3 results come from, so this is not a detail.
Error 3: forgetting the base burn
Raised-surface fabrics can show a surface flash: a flame that runs across the fibre tips without igniting the base fabric. The classification for raised surfaces depends on both the burn time and whether a base burn occurred.
An operator who only records the timer value cannot classify a raised fabric. Record, for every specimen, whether the base fabric ignited or fused. That observation must be made at the cabinet, during the test.
How classification works
The class is not decided on one specimen. Five specimens are tested first; if the results fall in the retest zone, five more are tested and the class is decided on ten.
Plain-surface fabrics
- Class 1 (normal flammability): no burn times, or an average burn time of 3.5 s or more.
- Class 3 (rapid and intense burning): in ten specimens, two or more burn times averaging under 3.5 s.
Raised-surface fabrics use a 4.0 s and 7.0 s structure combined with the number of base burns. In short:
- an average over 7.0 s is Class 1 whatever the base burns;
- an average of 4.0–7.0 s with enough base burns becomes Class 2;
- an average under 4.0 s with enough base burns becomes Class 3.
The exact counts of base burns that trigger each class differ between the five-specimen and ten-specimen stage, so work from the decision table in 16 CFR 1610.7, not from memory.
Error 4: testing only the original fabric
Fabrics are tested twice: in the original state and after refurbishing. Refurbishing means one dry-cleaning cycle followed by one laundering cycle, with the laundering done according to AATCC LP1 as cited in the regulation. Flame-retardant finishes and surface treatments can wash out; that is why the step exists.
The final classification is the more severe of the two results. A fabric that is Class 1 as received and Class 2 after refurbishing is a Class 2 fabric.
If your report shows only one set of burn times, it is not a 16 CFR 1610 report.
Error 5: misreading the exemptions
The regulation exempts some fabrics from testing when issuing a guaranty:
- plain-surface fabrics weighing 2.6 oz/yd² (about 88 g/m²) or more, regardless of fibre content;
- fabrics, plain or raised, made entirely of acrylic, modacrylic, nylon, olefin, polyester or wool, or blends of only those fibres.
Two traps follow. First, the weight exemption applies to plain-surface fabrics only — a heavy brushed fleece is not exempt by weight. Second, the fibre exemption is lost as soon as a non-listed fibre enters the blend. A polyester fleece with a small cotton or viscose component is no longer automatically exempt.
The regulation also excludes some products from its scope altogether, such as certain hats, gloves, footwear and interlining fabrics. Read 16 CFR 1610.1 before deciding a product is out of scope.
16 CFR 1610 and ASTM D1230
ASTM D1230 describes a very similar 45° test, and both are run in the same type of cabinet. They are not interchangeable on a report. When the customer is shipping apparel into the US, the regulatory reference is 16 CFR 1610; quote it, and quote the edition of the procedure you followed.
Practical checklist
- Were specimens oven-dried, cooled in a desiccator and tested within 45 s?
- Were raised surfaces brushed once, against the lay?
- Was a base burn recorded for every raised-surface specimen?
- Were both original and refurbished specimens tested?
- Was the exemption claim checked against both weight and surface type?
Our 45° flammability tester is built in our own workshop in Istanbul for 16 CFR 1610 and ASTM D1230 work; see the 16 CFR 1610 standard page for the related equipment.