The Complete Guide To UL 94 Ratings

UL 94 is a standard developed by Underwriters Laboratories (UL) to evaluate the flammability of plastic materials used in devices and appliances. The UL 94 Standard for Tests for Flammability of Plastic Materials for Parts in Devices and Appliances includes small-scale tests that evaluate the flammability of polymeric (plastic) materials, used for parts in appliances and components, in response to a small, open flame or radiant heat source under controlled laboratory conditions. The ratings are established using small-scale tests in which approximately 5 inch by ½ inch samples are subject to a ¾ inch, 50W tirrel burner flame ignition source. Two UL 94 ratings that are typical to come across are HB (horizontal burn) and V (V-0, V-1, or V-2).

What are the UL ratings?

Why are UL 94 ratings important?

UL 94 ratings are important because they provide a method for rating the ignition characteristics of plastic materials. Model building, life safety and fire codes are some examples of fields where products and materials often require specified minimum flammability ratings. Among other things, this includes tests to determine the hourly fire resistance ratings, surface burning characteristics of interior finish materials (flame spread and smoke developed), roof covering flammability ratings, flammability of contents within the building (such as mattresses, furniture, fabrics or floor coverings), and stored commodity classification, which are important to these industries where fire safety would be a concern. The results of most UL 94 flammability tests are not applicable to materials whose thickness exceeds 13.0 mm, or whose surface area exceeds a square metre.

What is the difference between V2 and V0 ratings?

The difference between V2 and V0 is that V2 is less stringent than V0. To achieve a V2 rating, the test samples must extinguish within 30 seconds after the test flame is removed, not burning to the top clamp or dripping molten material which ignites a cotton indicator. To achieve a V0 rating, the test samples must extinguish within 10 seconds after the test flame is removed, not burning to the top clamp or dripping molten material which ignites the cotton indicator.

What is the highest UL rating? 

The highest UL 94 rating is V-0. To achieve a V-0 rating, the test samples must extinguish within 10 seconds after the test flame is removed, while not burning up to the top clamp or dripping molten material which ignites a cotton indicator.

What is a UL94 HB rating?

UL 94 HB rating indicates that the material was tested in a horizontal position (horizontal burn) and found to burn at a slower rate than a specified maximum. 

What regulations require UL 94 Ratings? 

The model building, life safety and fire codes include numerous requirements that products and materials have specified minimum flammability ratings. Among other things, this includes tests to determine the hourly fire resistance ratings, surface burning characteristics of interior finish materials (flame spread and smoke developed), roof covering flammability ratings, flammability of contents within the building (such as mattresses, furniture, fabrics or floor coverings), and stored commodity classification . Two UL 94 ratings that code officials commonly run across are HB and V (V-0, V-1, or V-2). These ratings are established using small-scale tests in which approximately 5 by ½ inch samples are subject to a ¾ inch, 50W tirrel burner flame ignition source.

How do you achieve UL 94 HB and UL 94 V ratings? 

To achieve a HB rating, test samples, placed horizontally, burn slowly across the sample when the test flame is applied to the end of the sample. In this test, compared to other UL 94 tests, the sample is only exposed to the flame once, as opposed to at least 2 times in some of the other tests. For thicknesses of 3-13mm, the burning rate must be less than or equal to 40mm per minute, to achieve a HB rating. For thicknesses of less than 3mm, it must be less than 75mm per minute to achieve this rating. And if the flame is extinguished before the first mark (0mm per minute), it is also awarded a HB rating. To achieve a V rating (e.g. V-2, V-1, or V-0) the test samples, placed vertically with the test flame impinging on the bottom of the sample, must extinguish within specified times, not burning to the top clamp or dripping molten material which ignites a cotton indicator. 

What is low smoke material?

When discussing UL ratings, the term “low smoke material” pertains to the quantity of smoke generated by a cable when it is burned. The phrase “low-smoke, halogen free” is composed of two separate performance characteristics that must be evaluated in a cable. The “low-smoke” component relates to the smoke quantity produced by a cable during combustion. The “halogen free” part pertains to the presence of individual halogen elements (such as Chlorine, Bromine, Fluorine, and Iodine) in each flammable cable component. For a cable to be classified as low-smoke halogen free (LSHF), it must meet the criteria for both of these characteristics. UL Solutions provides optional halogen free (HF) and LSHF certification marks for all wire and cable categories, in accordance with the IEC 62821 series of standards.

What products do we sell with UL flammability ratings? 

Our ranges of nylon screws & bolts and nylon hex nuts are both produced from UL 94-V2 rated nylon 66.

We supply plastic snap rivets which are made from UL 94-V2 rated nylon 66 as standard, but are available in UL 94-V0 upon request.

We also offer liquid tight break through plugs and liquid tight threaded plugs, which are manufactured from rated UL 94-HB TPE and UL 94-V2 rated nylon 66 respectively.

Our metal cable glands are UL94-V0 rated, made of stainless steel (A2 and A4), or brass.

We manufacture both plastic cable ties and metal cable ties, which are made from UL94-V2 rated nylon 66, and UL94-V0 rated metal and either epoxy or polyester coating, respectively.