Control or monitoring of the LIP testing process: The fitness for purpose of the LIP standard products
Lower Ignition Propensity (LIP) is a product safety standard intended to increase the probability that a cigarette will self-extinguish under strictly controlled laboratory conditions. LIP compliance indicates that the probability that a cigarette taken from the population will self-extinguish under the conditions of the test is ≥87.5%. Test validity is ensured by adhering to the rigorous requirements concerning the environment, apparatus and materials, coupled with periodic testing of a control, reference and/or monitor whose characteristics have been established. These materials have different functions dependent upon the experimental context. For example, a control displays the characteristic of interest under the conditions of the test; a reference provides a basis for comparison with an unknown sample, and a monitor is used to assess the temporal stability of the analytical process. When using a reference or monitor it must be demonstrated that the analytical process being evaluated is measuring a homogenous characteristic. This may be established when it is notionally possible to obtain an unlimited range of finite values. However, when LIP is the characteristic of interest, the population from which samples are derived is considered heterogeneous by means of a mathematical construct in which the population contains both compliant and non-LIP compliant cigarettes. Statistical modelling demonstrates that a range of Full Length Burn (FLB) rates will be measured irrespective of the target FLB rate. Several target FLB rates have been modelled supporting the conclusion that the NIST standard is an appropriate control to ensure test validity due to the low probabilities of finding this non-LIP compliant and a 0% FLB rate. Given the rigorous conditions prescribed within the analytical methods it is uncertain what additional value is offered by the use of a reference or monitor when the aim is to ensure test validity.