General Passive fire protection is defined as any fire protectionsystem that by its nature plays an inactive role in the protection of person-nel and property from damage by fire. Appendix F contains additionalinformation on passive fire protection maintenance, rat- ings, andpenetrations. Passive fire protection is quite often generically referred to asStructural Fire Protection (SFP), particularly in governmental regulations.Examples of passive fire protection systems would be spray-on insulatingmaterials or insulating blankets of fireproof materials. Conversely, examplesof active fire protection systems would be tire water, APPP, CO, or drychemical 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 typesof fireproofing materials available and in use throughout the industry.
Thesematerials are lightweight con- cretes, preformed inorganic panels, masonryblocks and bricks, man-made mineral fibers, and subliming, intumescent, andabla- 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. FOAM SYSTEMS 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.Concentrate Proportioning. Foam concentrates are available for mixingwith water in fixed proportions; commonly, one through 6% mixtures with water.The correct amount of concentrate may be introduced directly into the firewater system by use o f either eductor stations or diaphragm tanks. I.Eductor Stations. A simple means to supply foam to a hose station isthrough the use of an eductor to pick up the foam and proportion it into thewater stream.
The main disadvantage of an eductor is the pressure loss acrossit (on the order of one- third). This loss must be taken into account in thedesign of a system. Conventional fire hose nozzles are available that willprovide sufficient aeration to form a foam. Because eductors are sensitive toback pressure, fixed rate nozzle gallonage rating and eductor ratings mustmatch. Manufacturers’ data should be consulted for maximum lengths of hose thatcan be used. 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.Premix Systems. Premix systems may be used when a self-contained firefighting system is desired. A means of storing the solution is required alongwith a means to expel the solution.
Commercial equipment is available for thispurpose and must be tai- lored to fit a particular application. Premixedfoam-water solutions should be periodically tested and replaced to ensure theirproper concentration and chemical integrity. DRY CHEMICAL SYSTEMS Drychemicals extinguish by interrupting the chemical reaction of the fire. Drychemical is very effective at reducing flame, but does not cool or providereflash protection. Dry chemical is most commonly used in portable orsemi-portable extinguishers, but may be used in hose reel or fixed systemapplications.
Fixed systems are typically employed over cooking surfaces ordeep fat fryers. Dry chemical is deployed as a powder driven by a compressedgas propellant. The powder poses risk of injury if inhaled, and can bedissipated by wind, reducing its effectiveness in exterior applications. Thepowder can be corrosive to electrical com- ponents. The nature of potentialfires should be carefully considered in selecting and sizing the type of drychemical and equip- ment. NFPA 17 Dry Chemical Systems should beconsulted when planning, designing, or installing dry chemical systems.
a.Types o/Dry Chemical Agents. Dry chemical agents are available for allclasses of fires. The terms “regular dry chemical” and “ordinarydry chemical” refer to powders that are listed for use on Class B andClass C fires. “Multipurpose dry chemical” refer WATERMIST SYSTEMS Watermist, or tinewater spray systems extinguish fires by rapid cooling effect, combined withlocalized displacement of oxygen at the flame source as the mist is flashedinto steam. Watermist systems may be used in applications suitable for a fixedgaseous or sprinkler system. Watermist utilizes stored fresh or distilled waterand leaves no residues. Electrical equipment should be de-ener- gized beforedeployment ofwatermist, although it can be safely discharged while electricalequipment is energized.
Types o fWatermist Systems. Watermistsystems may be designed to protect a single location or multiple locations. Thesystems come in two basic configurations: I. High-pressuresystems provide fresh water propelled by Nitrogen or other compressed gas atpressures of 150 psi – 4,000 psi.
Water is distributed by a singlehigh-pressure piping system to nozzles, where the water is atomized into a finemist 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 SystemConsiderations. Watermist systems typically use far less water thansprinkling systems. The space and volume requirements for watermist systems arecomparable to that for a fixed gaseous system.