Understanding Flammability Ratings: A Guide to Fire-Resistant Materials and Safety

When working in an industry that deals in high heat operations, it’s important to understand what different flammability ratings mean in order to ensure safety within the work environment. In this blog post, we dive into what each rating represents so you can make a better and more informed decision on your next purchase.

What is a flammability rating?

Plastics, wires, and interiors have specific manufacturing regulations they have to adhere to reduce risks in their applications. A flammability rating is the first thing a consumer, engineer, or designer will look at to gain a better understanding of these risks. The flammability rating of a product details the propensity of a specific material to ignite and spread a flame.

3 Most Common Flammability Tests and Ratings

UL 94

UL 94 is also referred to as the Standard for Safety of Plastic Materials for Parts. This plastics flammability standard was created by Underwriters Laboratories. It determines a material’s propensity to extinguish a flame or cause it to spread upon ignition.

When a product is UL 94-rated, it is commonly misconstrued as inflammable which is not at all true. The test only describes the characteristics of a specimen that has been ignited.

The six specified flame classifications are listed below from least flame-retardant to most flame-retardant:

• HB - slow burning on a horizontal specimen; burning rate less than 76 mm/min for thickness less than 3 mm or burning stops before 100 mm
• V-2 - burning stops in less than 30 seconds on a vertical specimen; flaming particle drips are allowed.
• V-1 - burning stops in less than 30 seconds on a vertical specimen; particle drips are allowed so long as they are not inflamed.
• V-0 - burning stops in less than 10 seconds on a vertical specimen; particle drips are allowed so long as they are not inflamed.
• 5VB - burning stops in less than 60 seconds on a vertical specimen; no drips are allowed; plaque specimens may develop a hole.
• 5VA - burning stops in less than 60 seconds on a vertical specimen; no drips allowed; plaque specimens may not develop a hole.

Under UL 94, there are multiple tests which are given their own classification designation. For example, the UL 94-V0 is a vertical burn test for which a V-0, V-1, and V-2 classification may be achieved depending on the results. The 94V-0 is the most difficult to accomplish and is the most commonly required by consumers.

VW-1 (UL 1581)

This Vertical Wire (VW) flammability test was developed in order to measure the flame retardancy of wires, sleeves, and similar products. A Tirrill burner is used instead of a Bunsen burner for a more controlled flame that is only applied for 15 seconds, removed, and then reapplied after another 15 seconds or once the flame ceases. This will be done for a total of five 15-second applications.

The pass/fail conditions for this test are described below:

• After the five 15-second cycles, a wire sample that has gone through the test must cease to burn within one minute.
• No more than 25% of the Kraft paper flag must be carbonized.
• Additionally, any dropping material must not ignite the surgical cotton placed at the bottom of the burner.

FAR 25.853

The Federal Aviation Administration designed this vertical Bunsen burner flammability test in order to provide guidance material for demonstrating compliance with the Federal Aviation Regulations (FAR) pertaining to the flammability of aircraft seat cushions.

The goal was to determine the maximum burn rate of the materials used in these applications in order to reduce the instances of burn injuries, or at the very least, the severity of said injuries.

The pass/fail criteria for these materials are based on the following:

• In a 60-second test, burning must stop within 15 seconds; any flaming material that falls from the test sample extinguishes within 3 seconds on average; farthest damage of the sample must not exceed 6” (152 mm) on average.
• In a 12-second test, burning must stop within 15 seconds; any flaming material that falls from the test sample extinguishes within 5 seconds on average; farthest damage of the sample must not exceed 8” (203 mm) on average.

More Flammability Tests and Ratings

The three aforementioned ratings cover a wide range of fire-resistant materials from plastics to sleeving. The following are flammability tests that are used in other industries pertaining to automotive and railway vehicles.

SAE J369

This standard was released by SAE International in order to determine the flammability of polymeric interior materials used in automotive vehicles and self-propelled machines from various industries (i.e. construction, agriculture).

FMVSS No. 302

Based on the practice developed by the SAE, the Federal Motor Vehicle Safety Standard was released in order to address fire safety in vehicle interiors. The standard was adopted in 1971 and specified a burn rate that does not exceed 102 mm per minute on materials within 13mm of the occupant compartment interior.

Test Method D45 1333

This standard was developed by PSA Peugeot Citroen group in Europe and explains the combustion behavior of materials used for the interior compartment of a car when exposed to horizontal and vertical flames. The principle of this standard’s test method is igniting the top of a test piece and observing its burn pattern.

EN45545-2

The European Railway Standard for Fire Safety affects manufacturers of all railway vehicles including high-speed, regional, and industrial trains. The railway vehicles are then classified in accordance with the fire hazard level: HL1, HL2, HL3, with HL1 being the lowest and HL3, the highest; associated with their design and operation.

NF F 16-101

The standard for French fire testing of railway components is described in NF F 16-101 (Railway Rolling Stock Fire Behavior Choice of Material) and NF F 16-102 (For Electrical Equipment). Rolling stock materials are tested and classified into burning behavior I rating; burning behavior M rating; and smoke and toxicity F rating.

Why do you need to know this?

It’s important to note that these tests are done in controlled environments with controlled flames. It is rare for a product to mimic the exact same conditions as its rating describes. The size, environment, and even the geometry of the product can change the burn rate and distance of any product.

However, fire safety is important in all fields which means that even just the basic knowledge of the flame retardancy of products that are commonly found in your work environment can reduce the risk to you and those you work with. Knowing the flammability rating of these specific materials will give you an insight as to how it ignites, spreads, and extinguishes flames.

These tests and ratings are placed on fire-resistant materials used in various industries to help you make an informed overall decision on the products you purchase. Work closely with a product specialist in order to find the right fire-resistant sleeving that best fits your application here at Titan Electronics!