ABS - 311
GUIDANCE NOTES ON GAS DISPERSION STUDIES OF GAS FUELED VESSELS
|Publication Date:||1 October 2019|
For vessels using gases or other low-flashpoint fuels, the ABS Rules for Building and Classing Marine Vessels (Marine Vessel Rules) (5C-13-6/7.2) require the vent exit of pressure relief systems to be located not less than one-third of the vessel breadth or 6 m (19.7 ft), whichever is greater, above the weather deck; 6 m (19.7 ft) above working area and walkways; and at least 10 m (32.8 ft) away from air intakes, air outlets or openings to accommodation, service and control spaces, engine combustion air intakes (5C-13-10/3.1.11 of the Marine Vessel Rules), or other non-hazardous areas.
Because of their size limits, it may be impractical for some small vessels to meet these requirements. The ABS Rules recognize this and allow alternative arrangements to be accepted on a case-by-case basis. An appropriate risk assessment based on a vessel-specific gas dispersion analysis is required in accordance with recognized standards (e.g., IEC-60079-10-1).
Computational Fluid Dynamics (CFD) has been widely recognized as a useful tool for assessing various engineering applications. In comparison to other approaches such as empirical correlations models (Chen & Rodi, 1980) and integral models (Lee & Chu, 2003), CFD is an advanced modeling technology which solves the conservation equations of mass, momentum, gas species, energy, and turbulence and provides detailed information on the gas cloud in both near and far fields. A summary of the capabilities and limitations of these modeling approaches can be found in Ivings et al. (2007).
These Guidance Notes provide the general information and guidelines for carrying out a gas dispersion study using CFD. These Guidance Notes were developed on the basis of industry experiences mostly for vessels less than 60 m (197 ft) in length and are not intended to address all aspects of gas dispersion CFD analysis. Application to larger vessels may need additional considerations.