UL94 Standard Operating Procedures

Purpose

The UL 94 Flammability Test is intended to provide an indication of the acceptability of polymeric materials used in devices and appliances based on their flammability characteristics. This is solely based on their response to a small open flame under controlled laboratory conditions.

Safety Procedures

Personal Protective Equipment

                Heat Resistant Gloves

                Safety Glasses

                Fire Resistant Jacket

                Long Pants

                Closed Toed Shoes

                Hair tied back for those with long hair

These tests must be performed under a fume hood to prevent inhalation of fumes and ashes from the burning materials.

Equipment

The following items should be available and used during testing: Bunsen burner, stand with a clamp holder, cotton pads, an accurate timer (a timer is available on the test apparatus, but an additional timer is useful), a conditioning chamber, and a lighter.

Sample Preparation

Two sets of five samples (ten total) of dimensions 125mm x 13mm x 3.175mm should be conditioned as follows: one set at 23 C and 50% RH for the 48 hours prior to testing and one set with no conditioning (as received).

Procedure

1. Ensure that the sample holder (the stand and clamp) is positioned in such a way that the sample will be held at least 425 mm above the working surface.
2. Place cotton pads directly below the clamp ensuring a 50mm x 50mm area is covered. Additionally, the thickness of the cotton should not exceed 6 mm.
3. Check that the valves for main and pilot at the back of the flame control module are closed. 
4. Use provided calibration strip (metal strip of specimen dimensions) in steps 5-12 to properly align the burner to sample. Once the apparatus is in alignment, begin at step 10 using the test specimen. 
5. Open the house gas line by moving the handle into the open position (parallel to the pipe). This valve is along the wall near the fume hood. Additionally the gas valve on the fume hood needs to be opened. 
6. First open the gas line to the pilot flame by turning the knob labeled pilot at the back of the apparatus. Use the lighter to ignite the pilot. Adjust the flame height by opening or closing the pilot valve.
7. Partially open the valve to the main Bunsen burner. No gas will flow until the switch on the controller is flipped on.
8. Flip the switch on the bottom of the controller to start the flow of gas to the main burner. The pilot burner should ignite the main burner. If it does not, adjust the height of the pilot flame. Note the gas will only flow for 11.4 seconds. If additional time is needed, press the reset button at the top of the controller’s front panel. Use this time to adjust the flame height of the burner via the valve at the back of the controller. It should be a 20±1 mm high blue flame.
9. Once the settings on both valves are adjusted, flip the switch to turn off the test.
10. Place the top 6 mm of the specimen vertically in the clamp. Adjust the holder so that the bottom edge of the specimen is 300±10 mm above the cotton as shown in Figure 1
11. Start the burning portion of the test by flipping the switch. 
12. Apply the flame to the midpoint of the bottom edge of the specimen for 10±0.5 seconds. The application point should be 10±1mm above the top the Bunsen burner. The apparatus should be set up close to these specifications already, but the burner will be on for 11.4 seconds. This will allow for minor adjustments to be made.  Additionally the Bunsen burner should be angled up to 45° to prevent dripping onto to the Bunsen burner. If dripping is present, it should fall onto the cotton underneath the specimen.  
13. A timer will start on the controller after the 11.4 seconds of burning finishes. If an additional timer is being used, start it when the burner extinguishes.
14. At this time, the specimen is most likely flaming. When the flaming burn stops, record this time as t1 and reapply the burner for another 10±0.5 seconds. To reapply the flame, use the reset button at the top of the controller.
15. If flaming ceases immediately on the specimen after the first removal of the Bunsen burner flame, immediately reapply the flame.
16. After removing the flame for the second time, the timer should be reset. This happens on the controller automatically when the reset button is pressed. Record the end of the flaming burn as t2.  
17. Without resetting the timer, watch for the end of the glowing burn period. Record the end of the glowing burn as time t3.
18. Record whether or not any flaming or smoldering has traveled up to the holding clamp.
19. Record whether or not the cotton beneath the sample was ignited from the specimen dripping.
    
    

    

    Figure 1: Schematic for UL94 Burn Test

Results

The following results should be recorded:

                t1: The flaming combustion time after the removal of the first flame

                t2: The flaming combustion time after the removal of the second flame

                t3: The glowing combustion time after the removal of the second flame

                Whether or not the specimen burned up to the holding clamp

                Whether or not the dripping from the specimen ignited the cotton

Flammability Criteria

The following table should be used to rate the material as V-0, V-1, or V-2, with V-0 being the most flame retardant material

If only one specimen from a set of five specimens does not comply with the requirements, another set of five specimens is to be tested.

In the case of the total number of seconds of flaming, an additional set of five specimens is to be tested if the totals are in the range of 51-55 seconds for V-0 and 251-255 seconds for V-1 and V-2.

All specimens from the second set should comply with the appropriate requirements in order for the material in that thickness to be classified V-0, V-1, or V-2. 

For more information, see the UL94 standard.

UL94-2013.pdf