The harsh environment of the arctic requires specialized safety solutions. An important safety issue in the arctic is the need for additional enclosed modules. Enclosed modules are used to prevent: ice and snow from process equipment; cold climate from imposing an unduly harsh working environment on the operators. Enclosed mechanically ventilated process modules differ from the open naturally ventilated process modules normally used in offshore facilities. The explosion safety performance of the non-standard mechanically ventilated process modules has been studied in detail through an extensive program of CFD simulations. Mechanically ventilated modules have explosion risk drivers distinct from risk drivers in naturally ventilated modules. Significant factors which primarily impact the explosion risk levels on confined process modules are: module size; HVAC philosophy; ignition source isolation efficiency; and the use of pressure relief panels. The impacts of these factors on explosion risk are discussed in this paper, along with significant conclusions to consider with future development in the arctic climatic environment.
The primary difference between enclosed and open modules is that any gas leak will be trapped inside the enclosed module. Only the HVAC system can extract the gas from an enclosed module (open module gas leaks can be directed out of the module, with accumulated flammable gas negligible). For all leaks (except smallest) in a confined module, the gas will accumulate relatively fast to flammable concentration levels and greater in large portions of the module. After the leak has stopped and the gas is slowly vented out of the module by the HVAC system, the rich gas will pass through flammable concentrations and form a large flammable gas cloud. This secondary peak of flammable volumes (first peak occurs soon after the leak with the growing gas cloud) is usually significantly larger and persists longer than the first peak. Safety systems which control the transient of the secondary peak (and the ignition intensity in this period) are seen to be significant in controlling the explosion risk.