Fire Protection Philosophy and Design Guide

FIRE PROTECTION PHILOSOPHY AND DESIGN GUIDE
PROCEDURE NO.
PTD-DGS-133
REV
0
DATE
Nov. 11, PAGE OF Fire and smoke alarms detect the fire and alert personnel to use along fire extinguishers. If normally unoccupied, some type of automatic non- aqueous extinguishment system might be considered.
VESDA (Very Early Smoke Detection and Alarm) systems have been used to detect very low levels of smoke and allow personnel to confirm the problem and use fire extinguishers or switch power through auxiliary wiring systems Storage Tank Farms
Storage tanks (for flammable liquids) and their containment areas experience pool fires and these are most effectively fought with foam. For flammable liquids, which are heavier than water, copious amounts of water can suffocate the fire. For flammable liquids, which are very soluble in water, copious amounts of water dilute and cool the burning liquid sufficiently to stop the fire. For flammable liquids, which are lighter than water, water will just spread the fire and is most appropriately used to make foam and to cool hot surfaces (which keep reigniting fires or keep producing flammable vapors or which would eventually lead to structural failure) and to cool adjacent tanks.
In relatively compact tank farm installations the use of fixed foam systems is considered appropriate. Several tanks can share such a system. They are activated manually (remotely or from a safe location) and the foam solution directed to the appropriate tank. A single source of foam is provided. Firewater flow is started which automatically begins educting foam. This foam solution travels to the target tank through a foam distribution network. Fixed systems are used in order to cut down on response time, which is of the essence in close quarters where neighboring tanks can be rapidly affected.
Fixed foam systems are also appropriate for closed tanks with no floating roof. In such tanks, any fire is a full surface fire. Any delay in application of foam or cooling water spray increases the likelihood that a foam layer will be impossible to form and a fully involved tank fire will ensue. Fully involved tank fires are very difficult to fight and are usually left to burnout. Focus is on protecting adjacent tanks and equipment, de-inventory of the burning tank, and prediction of when ‘boil-over’, ‘froth-over’, or tank unzip may occur.
For relatively spread out tank farms, and tanks with unsinkable internal floating roofs, semi-fixed foam systems maybe appropriate.

FIRE PROTECTION PHILOSOPHY AND DESIGN GUIDE
PROCEDURE NO.
PTD-DGS-133
REV
0
DATE
Nov. 11, PAGE OF For external unsinkable floating roof tanks, mobile foam systems maybe used.
Where the vapor space inside a storage tank is reliably padded, it is unlikely that flammability levels will be achieved and therefore foam application systems maybe waived. Passive protections:
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Frangible roofs are provided on storage tanks to minimize blast damage to a tank if ignition occurs.
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Flame arrestors are used to prevent back flash from a vent fire from entering the tank.
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Electrical shunts are used to ground floating roofs to sidewalls preventing ignition due to lightning (for external floating roofs) or due to static buildup on internal floating roofs.
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Air vents are used to maintain a high concentration of air inside a tank to stay out of flammability limits.
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Containment, grading, drainage, remote impoundment, intermediate berms are used to carry spilled hydrocarbons away from tanks, equipment, foam and process liquid lines LPG Storage Tanks
The storage of LPG’s shall be provided with remote impounding in accordance with the philosophy contained in API Standard 2510, Design and Construction of LPG Installations. The amount of and arrangement of the remote impounding shall be determined based upon the physical properties of the LPG, the climate conditions, and selected release scenarios
Many installations have used fireproofing to protect the tank supports and have provided deluge systems to protect the tank itself. Deluge systems may include a water spray or a simple dump of water on top of the sphere allowing the water to flow down over the surface in a film. To some degree this film also covers the bottom half of the vessel. Additional water spray is often also applied to the lower hemisphere of the vessel.
Usually, there are also two fire monitors located to be able to cover the bottom half of each tank.
In some recent cases, fireproofing of the entire vessel has replaced the use of water spray and deluge systems.

FIRE PROTECTION PHILOSOPHY AND DESIGN GUIDE
PROCEDURE NO.
PTD-DGS-133
REV
0
DATE
Nov. 11, PAGE OF LPG storage vessel leaks can produce vapor clouds, which explode if they reach an ignition source. Detection is the key to preventing this. Water spray to disperse, absorb, or knockdown the vapor is atypical method of preventing fire until the leak can be isolated. Provision for vessel flooding with water should be considered
If the LPG ignites before a vapor cloud is formed, then a vapor cloud cannot form. Do not putout the fire isolate the leak and allow it to burn out.
LPG fires are hot and radiant heat can start the production of vapors from the leaking LPG vessel or adjacent tanks. The vent system should be designed to carry away this vapor if not, relief valves start to open to the atmosphere releasing additional LPG vapors.
LPG leaks are often jets and when ignited may directly impinge on the burning vessel or adjacent vessels. If this impingement occurs above the liquid level of the vessel (which is probably falling due to venting, leakage, or de-inventory efforts, the shell will quickly fail, resulting in a BLEVE. This is the worst case LPG incident Offshore
Offshore facilities have the following characteristics:
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Limited opportunity for evacuation so protection of living control spaces is vital. Evacuation must be allowed for.
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The facilities are relatively expensive to build and are at the front end of profit centers. Staffing is at a minimum.
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The facilities are usually congested, so afire will spread rapidly if adjacent equipment isn’t designed to resist fire conditions.
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Excepting pipelines, the reservoirs of flammable liquids and gases are relatively small.
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Passive systems and automatic shutdown and isolation systems are prevalent.
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Water spray systems are often used.
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There is an abundant supply of firewater. All that is required is to pump it reliably and to have distribution piping to deliver it where required. Fire Water Pumps and Fire Protection System controls must be protected. Corrosion is an issue.

FIRE PROTECTION PHILOSOPHY AND DESIGN GUIDE
PROCEDURE NO.
PTD-DGS-133
REV
0
DATE
Nov. 11, PAGE OF Refer to the API RP series Cold Climate
Cold climate facilities have the following characteristics:
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The opportunities for evacuation are limited so protection of living control spaces is vital. Evacuation must be allowed for.
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The facilities are relatively expensive and are at the front end of profit centers. Staffing is at a minimum. The atmosphere is frequently very dry, contributing to static electrical discharges.
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It is difficult to maintain a large reservoir of liquid firewater.
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Passive systems and automatic shutdown and isolation systems are prevalent.
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Fire Water systems are often heated, heat traced, and inconstant circulation. High-pressure low-volume fine mist water spray systems are often used where firewater is required.

FIRE PROTECTION PHILOSOPHY AND DESIGN GUIDE
PROCEDURE NO.
PTD-DGS-133
REV
0
DATE
Nov. 11, PAGE OF 50

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