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Fire Water Pump Capacity Calculation Part 1 – Fire Zones Determination

Process safety and pressure relieving and depressuring system are two areas that I want to master. Since the topic is quite big, in this post I want to share you what I learnt about fire water pump capacity calculation, specifically how to determine fire zones.

Fire water pump capacity calculation begins with fire zones determination. The whole pictures of fire water pump capacity calculation is expressed in figure below.

Fire water pump capacity calculation
Fire water pump capacity calculation

To determine fire water pump capacity, we can say we determine fire water demandMaximum fire water demand is summation of fire water required for fixed system (water spray, foam, sprinkler) and fire water required for manual fire fighting equipment (fire hydrant, fire monitor, and hose reel).

Detail steps to calculate fire water demand is depicted in figure below.

Fire water demand calculation
Fire water demand calculation

I plan to create about six posts related with fire water demand calculation as shown in figure above.

  1. How to define fire zones
  2. Water spray and sprinkler calculation
  3. Fire monitor and fire hydrant calculation
  4. Foam system calculation
  5. Foam monitor and foam hydrant calculation
  6. Indoor hose reel system

Please support me! 🙂

In this first post, I will share you how to define fire zones.

When I was involved in well development project, I had an opportunity to prepare fire zones. How did I prepare it? I prepared it intuitively. I used my feeling, a bit logical, and simple calculation (how to make fire zones as minimum as possible but as logical as possible). I wondered if there is guidance to prepare fire zones.

After reading and browsing in several forums, I think this one is make sense for me: GS EP SAF 253 General Specification – Design of Field Facilities (Impacted Area, Restricted Area, and Fire Zones). So, in this post I want to share you about the specification.

What are Fire Zones?

Fire zones are the areas within the installation where equipment are grouped by nature and/or homogeneous level of risk at attached to them. Partition into fire zones results in significant reduction of risk level. This indicates that consequence of fire, flammable gas leak, or explosion corresponding to the credible event likely to occur in concerned fire zone, shall not impact other fire zones.

Fire zones are also created to segregate hazards and limit the probability of escalation. Simultaneous independent hazardous scenarios in two separate fire zones shall not be considered (single jeopardy concept).

How many Fire Zones commonly?

Number of fire zones should be reduced to minimize installation complexity, but it should be as small as possible to increase safety.

Fire Zone Partitioning

The main principle of fire zone partitioning is that it is not generally acceptable that a single credible event could result in the total loss of function of the plant.

  • For onshore facility, as a general rule, fire zone shall be separated by sufficient distance, for example at least 15 m between other process equipment
  • For offshore facility, as a general rule, fire zone shall coincide with platforms. However, certain platforms may be partitioned into more than one fire zone, if there are efficient physical protections (sufficient distance, blast wall) between two adjacent fire zones.

In particular, the following units and equipment shall be located in different fire zones:

  • Wellheads
  • Liquefied hydrocarbon storage
  • Liquid hydrocarbon storage
  • Process and utilities
  • Buildings
  • Hydrocarbon disposal systems (flares, cold vent)

This figures show example of fire zones in offshore facility:

Example of fire zones in platform
Example of fire zones in platform

One platform can be partitioned into more than one fire zone when there is sufficient physical protections. This figure shows that case:

Example of fire zones in platform 2
Example of fire zones in platform 2

For onshore facility, fire zones can be partitioned based on trains or units. This figure shows fire zones partitioned by trains:

Example of fire zones in onshore facility (partitioned by train)
Example of fire zones in onshore facility (partitioned by train)

While fire zones partitioned by units:

Example of fire zones in onshore facility (partitioned by units)
Example of fire zones in onshore facility (partitioned by units)

How large fire zones should be?

This question comes again. When we see example above, we ask a question, “Why fire zones building is divided into three fire zones?”. When zoning, there are several considerations that have to be taken into account:

  • Capabilities of fire-fighting means, for example:
    • Maximum practical range of fire monitors is about 45 m for a standard flow of 120 m3/h
    • The largest pool fire which can be extinguished by standard foaming agents is about 7000 m2
  • Access and operation of a fire-fighting team shall be possible for any combination of fire scenarios and weather conditions
    • Fire zones shall be convex and preferably rectangular
    • External fire monitors shall be located away from the edge of the fire zone
    • For onshore, the path between fire zones shall be straight and open at both end

Reference:

GS EP SAF 253 General Specification – Design of Field Facilities (Impacted Area, Restricted Area, and Fire Zones)

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