Fire protection of surface coatings

Abstract

Multilayer paint is a significant fire hazard particularly concerning rapid spread of flame,smoke and toxic species production. Fire protective coatings are often employed to protect this unpredictably flammable substrate from ignition (for example resulting from arson attacks in the communal areas of multi- occupancy buildings). Literature shows a gap in the understanding of this problem,a lack of suitable flammability tests,and methods for screening new fire protective coatings required to address this problem. This work investigates the factors affecting coating performance and develops screening test methods to estimate protection performance in standard fire tests. The dependence of these tests has been investigated with regard to substrate, coating thickness,composition of coating, thermal conductivity and rheological properties, to inform the development of modified coating formulations with enhanced fire safety.Coating materials have been investigated using thermogravimetric ana lysis (TGA) in both air and inert atmospheres and their burning behaviour using the cone calorimeter (ISO 5660). Novel screening test methods also include a test adapted from BS EN 367 for measurement of thermal conductivity, a thermocouple embedded in cone samples to assess the temperature profile at the substrate-coating interface and BS 476: Part 6 (adapted) as a scaled down version of the standard fire test. The chemical changes occurring during burning of current coatings formulations were investigated using CHN analysis, pyrolysis gas chromatography coupled with mass spectrometry (pyGC-MS),inductively coupled plasma coupled with mass spectrometry (ICP-MS),diamond attenuated total reflectance coupled with fourier transform infra-red (dATR-FTIR),nuclear magnetic resonance (NMR} and scanning electron microscopy coupled with electron dispersive X-ray analysis (SEM- EDAX} to inform the development of novel formulations.
Generally,intumescent formulations tend to exhibit lower fire propagation indexes when assessed in the BS
476: Part 6,longer time to ignition and lower peak heat release rates in the cone calorimeter, as well as reduced thermal conductivity recorded in the BS EN
367. Results report mixed performance,suggesting
that it is not only char residue formation that ensures a pass in the standard fire tests. Rheological properties
of the coatings are crucial to performance,with softening temperature and reduction in viscosity coinciding with gas release of the fire retardant additive. Each screening test method assesses one particular aspect of flammability, they are dependent on the controlled conditions under which results are collected,and the limited correlation observed with the performance in the standard fire tests, do not conclusively predict performance in a real fire situation.