FAIRFIRE - Fire fighting foams: Small scale fire test procedure

Small scale fire tests has many advantages

In the coming EN standard, EN 1568, the foam is tested against a 4,5 m2 heptane fire and a 1,73 m2 acetone fire. In the small scale method these fires are reduced to 0,66 m2 and 0,41 m2 respectively, e.i. with a factor 7 and 4. This meens of course many advantages, such as:

• reducing heat and smoke emission
• reducing the testing cost
• avoiding the disposal of large quantities of contaminated fuel
• being suitable for routine quality control tests
• allowing testing of a number of flammable chemicals and hydrocarbons
• permitting possibilities to study the effects of various parameters such as water quality, temperatures, foam ageing, preburn time, etc
• allowing cheaper and more environmentally friendly testing activity in the development of new foam concentrates

Small scale nozzle was developed

One of the main difficulties in reducing the scale of a fire test for foams is to achieve a foam generation with the same quality as in the larger scale. A different foam quality has been one of the main problems with some existing small scale fire test methods. A small scale version of the UNI 86 nozzle, specified in the coming EN 1568 and ISO 7203, was therefore developed by TRI. The nozzle is designated UNI 86 R and is providing the possibilities to achieve a foam solution flow rate of 1.48 to 3.00 l/min.

Correlation between standard scale and small scale verified by a large number of tests

The scaling work was made on empirical basis using time to control, time to extinction and time to burnback as correlation parameters. The variables investigated to achieve the best correlation with standard scale was tray size, tray geometry, nozzle position and application rate.The bulk of the scaling tests were performed with the same types of foam as used in standard scale. In total, 43 standard scale tests and 126 small scale tests were conducted at SP.

The analysis of the fire tests involved correlating mean data from small and standard scale tests for every combination of foam, proportioning rate and water quality that was tested both under the selected small scale conditions and the standard scale conditions. An overall comparison of fire performance grades generated by small and standard scale tests was made for each of the three fire types. The following correlation was achieved between the standard scale and small scale ratings:

These results are considered as very good although slightly lower correlation figures for Heptane/forceful. The correlation problems with the heptane/forceful tests were mainly related to that many of the tested foams were on the borderline between two classes.

The proposal to a small scale fire test procedure have been presented to the CEN working group on foam media, CEN TC191/WG3, who desides if the method shall be included in the future EN standard for foam, EN 1568.