There are two common types of fire that may occur in a hydrocarbon-processing complex: The first is a pool fire and this occurs when a flammable liquid leaks from a vessel or pipeline to form a fluid reservoir, which then ignites; The second, and potentially more dangerous type, is a jet fire which can happen following the rupture of a pressurised vessel and/or gas line.
A hydrocarbon pool fire will generate temperatures of more than 1000 Celsius within ten minutes of ignition with heat fluxes of around 150kW/m2. A jet fire will exhibit the same temperature rise, but the heat flux could be double that of the pool fire. Three distinct types of passive fire protection products are normally used in hydrocarbon-processing complexes:-.
- Cementitious products generally based on Portland cement plus lightweight aggregates. Cementitious materials protect the steel in two ways. Firstly, they contain trapped moisture, which in a fire situation will boil and keep the steel temperature around 100 Celsius until all the water has disappeared. The product then acts, secondly, as an insulator.
- Intumescent coatings generally epoxy based spray or hand applied. In the event of a fire these coatings intumesce (i.e.they swell to many times their original thickness) to form a tough insulating char.
- Blanket systems made from man-made fibres which use insulation as their primary fire protection mechanism. They are used primarily for cable tray and valve protection.
In order to protect structures against hydrocarbon fires in an onshore petrochemical complex, steel (such as that in piperacks and vessel skirts) is fire proofed with passive fire protection products that have been fire tested to the appropriate standard. Hydrocarbon standards/tests include BS476: Part 20; 1987 Appendix D, Underwriters Laboratory 1709, and the Norwegian Petroleum Directorate 'H' Class Test. Products used for onshore protection are applied at thicknesses that prevent the collapse of the steel for a certain time period.