 This particular one relates to the construction products regulations and is the results of the mistaken claim by one system manufacturer that the smoke classification of S1 is higher than that of S1A or S1B. The duration of the EN5399 test used to classify the smoke production is 20 minutes, during which time a 20.5 kilowatt flame is applied to the test sample. Typically this involves 24 individual cables that are attached to a ladder in a vertical test chamber. The smoke production classification has three levels. S1 having the following limits. Total smoke production of 50 square meters with a peak smoke production rate of less than 0.25 square meters per second. S2 is less than 400 square meters at a rate of no more than 1.5 square meters per second. Lastly S3 is very simple. It does not meet either S1 or S2. Now to clear up any confusion. If you pass S1 you can then opt to add an additional test to establish what is termed transmittance. This test is not new to us and we've been using it for a number of years to qualify an LS0H cable and it is related to smoke capacity or density. Effectively it is the amount of light that can be measured through the smoke produced. More than 80% is classified as an S1A and between 60 and 80% it is S1B. Below 60% it is a fail and could actually impact upon the claimed S1 rating. In conclusion having just S1 is not good enough as the majority of countries have declared or intend to declare a minimum requirements of S1B. The UK being one of them. Furthermore if you only have an S1 cable it could be argued that you're taking a backward step. If you don't establish the smoke density by way of additional or third-party verification testing. We trust this has cleared up any confusion.