Flame tests outer cover comparison - The development of pressure relieving devices by using thr

Sample K Sample A

Carol Diane Hepburn 178 | P a g e

6.5 Analysis of the experimental results

The aim of these bench-level experiments was to determine the potential flammability behaviour of the prototype wheelchair cushions. Some of the areas of potential use for these prototypes are in the healthcare sector. Some of the regulations applicable to the healthcare sector require wheelchair cushions to pass some of these standards: BS 5852 Ignition Source 5 (Crib 5); BS 7175: 1989 Section 3 Ignition source 5; BS 5852 Part 1 Ignition Source 0; and BS 5852 Part 1 Ignition Source 1. More details on this can be found in Chapter 3. In particular, it was important that these prototypes had the potential to pass the BS 5852 Ignition Source 5 (Crib 5) test. Therefore, these experiments would be used to determine this viability.

Sample A, which represented the basic configuration of the prototype wheelchair

cushions ASD4, ASD4-S and ASD450-S, with an outer PU cover, incorporated one layer of the FR viscose fabric M6810. This combination produced good results at the 10 second exposure stage, protecting the main core sections of the sample which was the thicker spacer fabric M8960. The two outer layers, the PU layer and the FR layer, self-extinguished almost immediately after the removal of the source flame at 10 seconds. At the 20 and 30 second flame exposure, subsequent layers were affected and the following occurred at layer 3. The stretch spacer fabric M3250 and layer 4, the

soft spacer fabric A1301-235 – burning and melting; scorching and melting or only

scorching. However, once again, the core layer M8960 remained intact, with no scorching in some cases.

The speed at which total self-extinguishing occurred was nearly always determined by the behaviour of the PU layer. The burning behaviour of the PU layer could include, significant melting as well as burning, especially if the flames began to climb up the sample, dropping molten PU onto the FR layer. Observations revealed that the FR layer always self-extinguished, but the total extinguishing of the flame for the whole sample was determined by, whether the PU layer just melted, or burnt and melted. If the FR layer was unable to stop the PU layer catching light & burning, then when the flame was removed the PU continued to burn and melt. Therefore, burning continued until the PU layer self-extinguished, not the FR layer, which did not burn after the removal of the flame. Therefore, even though this combination had the potential to be flame resistant, there was a need for more protection. Therefore, sample B was created.

Carol Diane Hepburn 179 | P a g e

Sample L was also created with a second FR layer, however the FR layers were

separated, by laying them either side of the stretch spacer fabric M3250. This was to investigate a further increase in flame resistance. Both samples exhibited the ability to self-extinguish almost immediately or within the 2-minute pass criteria. Both samples protected the core layer M8960, with the soft spacer fabric layer A1301-235 exhibiting only slight scorching, to more severe scorching, however no burning or melting was seen at this layer from a flame application of 40 seconds. The arrangement of layers used in samples B and L appeared to be the best configurations, as judged by these bench-scale tests, indicating the potential for these two configurations to pass the BS 5852 Ignition Source 5 (Crib 5) standard test. The prototype cushions needed to conform to this standard with a waterproof outer cover in place, due to the intended use of these cushions in the healthcare sector. The PU fabric used in these tests would be used to make that cover. Sample K, although similar in configuration, did not need to be waterproof to meet some of these regulations in the domestic sector. In comparison, samples A and K performed well against each other, however, the spacer fabric cover appeared to create a more ‘controlled burn’ initially. The polyester knitted spacer fabric M3730 melted during the application of the flame, rather than burned, which assisted both the FR and the polyester spacer layer to quickly self-extinguish. This is demonstrated in Tables 6.5 and 6.6, also Figure 6.35, in the after-burn times collected for these samples. Although both sample configurations gave good test results, the spacer fabric cover self-extinguished much quicker in general, than the PU fabric cover. This meant that the potential for the prototype wheelchair cushions to pass the BS 5852 Ignition Source 5 (Crib 5) standard test was good when using either, a waterproof outer cover (PU fabric) or a knitted spacer fabric outer cover (M3730). Overall, the bench-level tests were successful in determining the potential flame resistance of a selection of effective experimental configurations for the prototype wheelchair cushions. The final configurations for the prototype cushions can be seen in Tables 6.10 and 6.11.

Carol Diane Hepburn 180 | P a g e

Table 6.10. Basic composite construction: Prototype ASD4-S with PU cover

LAYER QUALITY DESCRIPTION

Outer Cover – 4 PU Interchangeable Outer cover – water proof

Inner cover – 3 M6810 FR protection cover – sealed

Inner cover – 2 M6810 FR protection cover – sealed

Inner cover – 1 M3250 Stretch cover – sealed

Core – 1 A1301-235 Soft moulding spacer layer

Core – 2 M8960 Castellated - Recess, Abductor and Adductor layer

Core – 3 M8960 Recess layer

Core – 4 M8960 Flat layer

Core – 5 D0100-03 Rigid base layer

This configuration has been fully tested externally and successfully met the BS 5852:2006 Ignition Source 5 (crib 5) see Table 6.9

Table 6.11. Basic composite construction: Prototype ASD4-S with spacer fabric cover