Pool size를 산정할 때 surface drainage를 고려할 수 있는가?

HSE-RM-ST09

7.7. FIRE ASSESSMENT

Pool Fire:
While studying the pool fire assessment consideration shall be given to following:

 

• While determining the size of the pool and spread, the facilities surrounding such as drainage facilities, dyke etc. shall be considered. Empirical models does not take these into account and thus may provide very conservative results for large and full bore releases which may be unrealistic;
• Many available pool fire models determine size of the pool based on release rate comparison with either burn rate or evaporation rates. Considering various drainage facilities, gutter provisions, obstructions, and upon ignition the burn rate is considerable higher than evaporation rates, evaporation rates are generally governing in determining long duration fires and hence pool size shall be considering these rates;

7.11. FIRE ZONE ASSESSMENT
Fire zones are areas of the plant sub-divided  based on the potential for fire & explosion hazard, as assessed by the consequence & risk modeling and the efficiency of response means and protective equipment. Fire zones are areas within the installation where equipment are grouped by nature and/or by similar level of risk attached to them. Fire zone assists in managing the separation distances between independent plant, emergency shutdown, flare design and defining firewater requirements.
The partition into Fire zones is such that the consequence of fire, a flammable gas leak or an explosion corresponding to the worst credible event likely to occur in the concerned fire zone shall not impact other fire zones to an extent where their integrity could be put at risk. The partition into fire zone is intended to limit the consequence of credible events but is not intended to avoid the occurrence of the credible events. A fire zone may be physically separated from other areas by space, fire barriers, diking, special drainage (e.g. impoundment basis) or by a combination of these so that fire is expected to be contained within that area. The escalation of the event is restricted to the affected fire zone and a minor impact on adjacent fire zones only.

 

SP-1258 QRA & PEM

A5.2.3.4 Pool Fire Modelling

In such cases where pool geometry is not known (e.g. free run on different types of surfaces with no restrictions) one of the scenario that can be modelled is assuming (somewhat immediate ignition i.e. ignition before the pool spreads in wider area) the fuel being consumed in pool fire as it is released. With such assumption equilibrium diameter (a diameter at which the pool does not spread further) can be calculated using the formula given below. By using the equilibrium diameter calculate pool fire effects using the stand-alone Pool Fire scenario in FRED.

 

The diameter of an equilibrium pool fire (i.e. where all the fuel is being consumed as it is released) is easily calculated by equating the mass release rate over the pool surface with the burning rate.

 

Drainage system design 

DEP 34.14.20.31 Drainage systems and primary treatment facilities 

Drainage layout plan 등을 참조하여 가능한 maximum pool size를 정할 수 있다. Modeling 결과의 신뢰성을 높일 수 있다. 

 

DNV Phast에서는

(1) Maximum pool size를 직접 규정할 수 있음. (단 pool thickness는 규정할 수 없음). 

(2) **pool fire 시나리오에서 pool size (pool diameter)**를 계산할 때, 일반적으로 사용자가 직접 burning rate (연소 속도)를 입력할 수 없습니다. 대신, Phast 내장 모델이 자체 수식 및 물성치, 환경조건 등을 바탕으로 자동 계산함. (by ChatGPT). 

=> 이는 DNV PHAST 자료를 통해 확인이 필요하다.

[Ref.] AN INTEGRAL MODEL FOR POOL SPREADING, VAPORISATION AND DISSOLUTION OF HYDROCARBON MIXTURES (DNV GL London)