Target of design for Fire Protection

Fire prevention은 화재/폭발 예방. fire triangle이 동시에 같은 장소에 존재하지 않게 함으로써 화재를 예방하는 것이 목적임. Ignition control과 유사한 개념. 

반면에, Fire protection은 small fire가 large fire로 escalation하지 못하게 하는 것이 목적.

• 설비 design 측면에서 large fire를 대상 및 기준하는 것은 적절하지 않다. small fire를 대상으로 하는 것이 맞음

 

Definition of Small fires.

Large fires에 반대되는 개념임. 

• Large fire may threaten personnel outside the vicinity of the initial fire and even endanger the whole platform or plant.
• Small fire는 controllable fire로 escalation을 야기하지 않을 정도의 fires라고 정의할 수 있다. 즉, escalation을 예방하기 위한 여러 안전장치에 기준이 되는 fire zone/sectionalized zone/process segment 범위 내에만 영향을 줄 수 있는 fire임. Not impact to nearby process equipment resulting in loss of containment and release of significant quantities of combustibles

Fire protection system design을 위한 FHA 혹은 CA/QRA를 수행하는데 flammables의 leak size는 작게 적용하는 것이 바람직하다.  API RP 581이나 PSM에서 규정하는 worst case/alternative case의 leak size는 large fire를 초래하므로 design에 적용하는 leal size로 활용하는 것은 합리적이지 않다. 

 

References 

API std 521 (2020)

4.4.13.3 Confined Pool Fires

It is up to the user to determine the type and size of the pool fire used for design of protection systems (e.g. pressure relief, depressuring, fireproofing). Where the main objective with respect to fire protection of process piping and equipment is to prevent a small (and controllable) fire from escalating to a larger (and uncontrollable) fire, then the large confined fires can be disregarded and the confined fires can be modeled as an open fire. 

 

Guidelines for the Protection of Pressurized Systems Exposed to fires, Scanddower (2004) 

3. General Principles

The main objective in this context is to prevent a small (and controllable) fire to escalate to a larger (and uncontrollable) fire that may threaten personnel outside the vicinity of the initial fire and even endanger the whole platform or plant.

Hence, a key issue is to prevent escalation to nearby process equipment resulting in loss of containment and release of significant quantities of combustibles.