General Passive fire protection isdefined as any fire protection system that by its nature plays an inactive rolein the protection of person- nel and property from damage by fire.
Appendix Fcontains additional information on passive fire protection maintenance, ratings,and penetrations. Passive fire protection is quite often generically referredto as Structural Fire Protection (SFP), particularly in governmentalregulations. Examples of passive fire protection systems would be spray-oninsulating materials or insulating blankets of fireproof materials. Conversely,examples of active fire protection systems would be tire water, APPP, CO, ordry chemical systems. API Publ 2218 Fireproofing Practices in Petroleum andPetrochemical Processing Plants can provide useful information regardingfireproofing practices, materials, etc. Uses Generally,passive fire protection is not used as the only means of fire protection, butrather it is used in concert with active fire protection systems.
This isbecause passive fire protection does not, in and of itself, provide inherentprotection and is normally effective only for a finite time period. Oncepassive fire protection is exhausted, the protected component is vul- nerableto damage by fire. Examples of where passive fire protection is used are:critical structural steel, living quarters, firewalls, etc. FireproofingMaterials Them are many types of fireproofing materials availableand in use throughout the industry. These materials are lightweight con-cretes, preformed inorganic panels, masonry blocks and bricks, man-made mineralfibers, and subliming, intumescent, and abla- tivemastics. However, the fireproofing materials that have been most commonly usedin the offshore petroleum industry, and which will be addressed here, can bebroken down into two generic groups; active and inactive insulants. The activeinsulants undergo chemical and physical changes when exposed to fire and theinactive insulants do not. Activefnsulants.
The active insulants are generally available asceramic fiber (or similar fireproof materials) structures in an epoxy-basedmatrix which contains additional chemicals designed to cause some chemical orphysical reaction upon exposure to heat. The active insulants typically areavailable in multiple-part mixtures which when mixed together form a slurrysuitable for spray application. However, they can be purchased in pre-castpanels which can be bolted in place. Active insulants are also known asintumescent materials because when they are exposed to heat, they undergo aphysical and chemical change which causes them to expand to several times theirapplied volumes, thereby providing enhanced insulation. InactiveInslliants.
The inactive insultants can be grouped into twogeneral groups: cementitious materials and man-made fibers, such as ceramicfiber or mineral wool. The cementitious materials, as the name implies, areessentially cement-based mate- rials of a fire brick refractory blend, whichare normally mixed as a slurry and spray-applied; however, these materials arealso available in precast slabs which can be bolted in place. Man-made fiberinsulants come in many different forms: blankets, bulk, panels, etc. Thesesystems are installed by mechanically supporting them in or on a wall orsimilar structure. FoamSystems Foamforming additives increase the effectiveness ofwater in controlling pooledliquid-hydrocarbon fires.
A tire fighting foam is a stable aggregation of smallbubbles of lower density than water or oil having a tenacious quality forcovering and clinging to horizontal or inclined surfaces. It has the capabilityof flowing freely over a burning liquid surface, cooling the liquid, and form-ing a tough, air-excluding, continuous blanket to seal combustible vapors fromaccess to air. Foam systems are not effective on gas pressure tires or gratedareas. NFPA 11 Foam Extinguishing Systems should be consulted whenplanning, designing, or installing foam systems. Foamsmay be employed using (I) hose stations, (2) fixed systems, or (3) portableextinguishers and should capable of being actuated manually. The foaming agentmay be applied by directly introducing foam concentrate into the fire watersystem or may be applied as a premixed solution of concentrate and water. Foammay be stored in a tank or in the vendor’s shipping container. The storagelocation(s) of foam concentrate and premixed solutions should be selectedconsidering the difficulty to replenish the system during an emergency, and theminimum ambient temperature because foam concentrates and premixed solutionsare subject to freezing.
The foam concentrate must be kept in ade- quate supplyand not contaminated or diluted and the operator should follow themanufacturer’s recommendation for testing. When dry chemical and foamextinguishing agents can be used at the same location, compatibility of the twoproducts should be confirmed with the manufacturer(s). a. ConcentrateProportioning. Foam concentrates are available for mixing with water infixed proportions; commonly, one through 6% mixtures with water. The correctamount of concentrate may be introduced directly into the fire water system byuse o f either eductor stations or diaphragm tanks.
I. EductorStations. A simple means to supply foam to a hose station is through theuse of an eductor to pick up the foam and proportion it into the water stream.The main disadvantage of an eductor is the pressure loss across it (on theorder of one- third). This loss must be taken into account in the design of asystem.
Conventional fire hose nozzles are available that will providesufficient aeration to form a foam. Because eductors are sensitive to backpressure, fixed rate nozzle gallonage rating and eductor ratings must match.Manufacturers’ data should be consulted for maximum lengths of hose that can beused. Actual length of hose used should not exceed the manufacturers’recommendation less equivalent lengths of fittings, etc., downstream oftheeductor. Eductor concentrate hose stations can be provided in a packagecontaining all the components pre- assembled, including a concentrate storagetank. b. PremixSystems.
Premix systems may be used when a self-contained fire fightingsystem is desired. A means of storing the solution is required along with ameans to expel the solution. Commercial equipment is available for this purposeand must be tai- lored to fit a particular application. Premixed foam-watersolutions should be periodically tested and replaced to ensure their properconcentration and chemical integrity.
Dry Chemical Systems Drychemicals extinguish by interrupting the chemical reaction of the fire. Dry chemicalis very effective at reducing flame, but does not cool or provide reflashprotection. Dry chemical is most commonly used in portable or semi-portableextinguishers, but may be used in hose reel or fixed system applications. Fixedsystems are typically employed over cooking surfaces or deep fat fryers. Drychemical is deployed as a powder driven by a compressed gas propellant. Thepowder poses risk of injury if inhaled, and can be dissipated by wind, reducingits effectiveness in exterior applications. The powder can be corrosive toelectrical com- ponents. The nature of potential fires should be carefullyconsidered in selecting and sizing the type of dry chemical and equip- ment.
NFPA 17 Dry Chemical Systems should be consulted when planning, designing,or installing dry chemical systems. a. Typeso/Dry Chemical Agents. Dry chemical agents are available for all classes offires. The terms “regular dry chemical” and “ordinary drychemical” refer to powders that are listed for use on Class B and Class Cfires. “Multipurpose dry chemical” refer Watermist Systems Watermist, or tine water spray systems extinguish firesby rapid cooling effect, combined with localized displacement of oxygen at theflame source as the mist is flashed into steam. Watermist systems may be usedin applications suitable for a fixed gaseous or sprinkler system. Watermistutilizes stored fresh or distilled water and leaves no residues.
Electricalequipment should be de-ener- gized before deployment ofwatermist, although it canbe safely discharged while electrical equipment is energized. Types o f Watermist Systems. Watermist systems may be designed to protect a single location ormultiple locations. The systems come in two basic configurations: I. High-pressure systems provide fresh water propelledby Nitrogen or other compressed gas at pressures of 150 psi – 4,000 psi.
Wateris distributed by a single high-pressure piping system to nozzles, where thewater is atomized into a fine mist as it passes through an orifice.2. Low-pressure systems operate at under 150 psi. Water and compressed air areseparately piped to each nozzle, where they mix to create a mist. b.
Fixed System Considerations. Watermistsystems typically use far less water than sprinkling systems. The space andvolume requirements for watermist systems are comparable to that for a fixedgaseous system.