Compliance
Fire performance of acrylic: what the ratings mean and when you need one
Standard acrylic burns. Flame-retardant grades burn much less readily, and the difference is documented by a test report rather than by a supplier assurance.
Compliance
Standard acrylic burns. Flame-retardant grades burn much less readily, and the difference is documented by a test report rather than by a supplier assurance.
Acrylic is a thermoplastic that will burn if a flame is held to it, and it drips as it burns. That is true of standard PMMA, and it is why some applications cannot use it at all, and why others specify a flame-retardant grade that costs noticeably more and is slightly less clear.
| Rating | What it tests | What it does not tell you |
|---|---|---|
| UL 94 V-2 | Vertical burn on a small specimen; burning drips are allowed but must not ignite cotton below | How the material behaves in a real fire, or at full scale |
| UL 94 V-0 | Vertical burn; burning stops within 10 s, with no dripping that ignites cotton | Flame spread across a large surface |
| UL 94 HB | Horizontal burn, the least demanding horizontal rating | Almost nothing about vertical flame behaviour |
| EN 13501 building class | Reaction to fire at a defined scale and mounting | Small-part behaviour |
| ASTM E84 Class A, B, C | Surface burning characteristics of a lining material | Component-level performance |
V-0 and V-2 are small-scale tests. A material that passes V-0 at 3 mm may fail at 1.5 mm, and the rating is always quoted with a thickness. A supplier who says V-0 without a thickness and a report has not given you a specification.
| Property | Standard cast PMMA | Flame-retardant PMMA |
|---|---|---|
| UL 94 at 3 mm | HB or unrated | V-2 or V-0 depending on grade |
| Clarity | Water-white | Slightly warmer, very slightly hazy |
| Cost | Baseline | Typically 1.5 to 2.5 times the standard sheet |
| Availability | Stock in most thicknesses | Ordered in, longer lead time |
| Machining | Standard | Standard, slightly more brittle |
| Colour range | Wide | Limited, mostly clear, opal and a few tints |
| Use it when | General fabrication, displays, guards without a fire requirement | A code, an insurer or a customer standard demands a rating |
For a retail display, a machine guard in a non-classified area, or a signage face, a fire rating is usually not required by any code. Specifying an FR grade there is money spent on nothing, unless the customer own standard asks for it.
We supply the sheet manufacturer report with the shipment where an FR grade is specified. What we cannot do is certify a rating ourselves: the rating belongs to the sheet, tested at a thickness, not to the part we machined from it.
Yes. Standard PMMA ignites and burns with dripping. Flame-retardant grades resist ignition and self-extinguish in the UL 94 test, but they are still combustible.
We can supply the sheet manufacturer UL 94 report for the grade and thickness used. The rating applies to the sheet as tested, not to the machined part, and we state it that way rather than issuing our own certificate.
Slightly. It is marginally warmer and very slightly less clear than standard cast acrylic, which matters on an optical or high-end display part. For a guard or an enclosure it is not noticeable.
It depends on the grade. FR polycarbonate can achieve V-0 with better impact performance, but it yellows outdoors and costs more. The choice is driven by the rating required and the other service conditions.
The thickness at which the rating was achieved. A V-0 rating at 3 mm does not automatically apply at 1.5 mm. State the part thickness and ask for a report at that thickness.
A flame-retardant claim is only as good as the document behind it, and the document that gets accepted is rarely the one printed on the supplier's website.
| Document | What it actually says | What it does not say |
|---|---|---|
| UL 94 V-0 / V-2 sheet report | A 125 mm specimen of a stated thickness self-extinguishes within a stated time | How a finished 3 mm part behaves, or how a building code classifies it |
| EN 13501-1 classification | A reaction-to-fire class for the product as tested | That the class applies to a different thickness or colour |
| Mill certificate | Grade, batch, and compliance statement from the sheet maker | Anything about the fabricated part |
| Building code flame-spread class | A class (A, B, or a national equivalent) for an interior finish | Whether your authority accepts the test standard |
Two traps. First, thickness matters: a V-0 result at 6 mm does not transfer to 2 mm, because the burn behaviour changes with section. Specify the thickness the test was run at, or expect the certificate to be rejected. Second, colour matters on some grades — pigments can change the result, so a black FR sheet and a clear FR sheet may not share a classification even when they share a data sheet.
The practical approach is to ask the sheet supplier for the report at the thickness you intend to use, in the colour you intend to use, and to keep that document with the batch card. That single habit answers the question a fire officer actually asks, which is not "is acrylic flame retardant" but "show me the test on the material in this panel".
If a standard or a customer specification requires a rating, send the clause and the thickness and we will quote the grade that meets it with its report.