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Saving lives with coatings

The essentials of passive fire protection.Paul Mather.Passive fire protection by means of intumescent,cementitious or ceramifying coatings or layers has gainedimportance in recent years. What are the specificrequirements on such systems?Passive fireproofing is the use of insulating systemsdesigned to deter heat transfer from a fire to the structurebeing protected. These are generally coatings but alsoinclude insulating panels or blankets. In most cases passivefire protection materials are used in conjunction with "active"systems such as water sprays, sprinklers or inert gassuppression. In contrast to active fire protection systemsPFP systems should be 'install and forget' solutionsperforming to the specified standard throughout thecomplete lifecycle of the structure, with minimal operationalmaintenance. The specification of a suitable PFP product fora project is usually based on a number of factors includingfire type, duration, substrate material and type andenvironmental location. Fire test approval is one of the mostimportant factors in assisting correct specification.

A growing demand for passive fire protectionPassive fire protection (PFP) systems are applied tostructural building components (steel, concrete) to preventthe rapid heat transfer which would lead to early failure incase of a fire. PFP safeguards the structural strength ofsteelwork, the integrity of divisions and protects personneland equipment for the duration of a fire or during escape.The collapse of the New York City World Trade Centertowers, following the terrorist attacks of 11 September 2001,was the worst building disaster in recorded history, killingsome 2,800 people. In response to this tragedy, the U.S.National Institute of Standards and Technology (NIST)conducted a three-year building and fire-safety investigationto study the factors contributing to the probable cause, orcauses, of the post-impact collapse of the towers. The NISTexpanded its research in high-priority areas such as fireresistive coatings for structural steel and issued a number ofrecommendations.Concerning PFPs, the NIST specifically recommended: "Theprocedures and practices used in the design of structuresfor fire resistance should be enhanced by requiring anobjective that uncontrolled fires result in burnout withoutpartial or global (total) collapse. Performance-basedmethods are an alternative to prescriptive design methods.This effort should include: (1) the development andevaluation of new fire resistive coating materials andtechnologies, and (2) the evaluation of the fire performanceof conventional and high-performance structural materials(such as fire-resistant steels and concretes)."As a result of these recommendations, there is a growingdemand for passive fire protection, particularly for materialsthat can be shop applied (offsite). This development isbringing onto the market new technologies which meet thechanging needs of owners and contractors. The introductionof these unique products give savings to owners ofbuildings, contractors and applicators and, combined withimproved aesthetics, are opening up new possibilities forspecifiers, project designers and architects.

Many types of fire need to be dealt withPFP products fall under specific performance categories,usually determined by the type of fire they are designed towithstand. These types of fire, often called fire loads, have a

distinctive time/temperature relationship (except jet fireswhich have a specified fuel load) which is used to categorizethe level of severity:

Cellulosic firesHere the fuel is natural carbonaceous type materials suchas wood and paper (Figure 1). These fires have relativelyslow heat rise and a peak temperature of 950°C.

Hydrocarbon firesThis represents fires fuelled by oil spills or gas clouds, whichare characterized by higher heat fluxes and fasterattainment of a maximum temperature of 1100°C. After thePiper Alpha Platform fire in 1988, protection againsthydrocarbon-fuelled fires has become the norm for theoffshore industry.

Jet firesA unique type of hydrocarbon fire caused by pressurizedgases or fuels that are released through an orifice and thenignited. These produce even higher heat fluxes: peaktemperatures can exceed 1200°C and generate highlyerosive forces.

Rapid rise firesThese occur in a confined space and/or when the fuel ishighly flammable, as in tunnel or nuclear fires.

Testing PFP ProductsIn every country, rules, regulations and building codesprescriptively specify the level of fire protection that isrequired for different structures: for example "60 minutes fireprotection". However, there is a trend towards providing alevel of protection commensurate with the risk and hazardinvolved - a "Fire Engineering" approach.The performance properties of a PFP product normally haveto be assessed by a fire test, prior to certification. Such testsare defined by specific national and international standards.These provide a methodology for proving compliance withthe fire resistance levels set for different fire types as set outin standard time/temperature curves (Table 1). Although firetest standards can be complex because of the sheernumber available, more established ones like BritishStandards (BS), ASTM International, UnderwritersLaboratories (UL) and the EN13381 European Standard arewidely used internationally.Whether the fire resistance is defined by prescriptiveregulation or by risk/hazard assessment, the level ofresistance for structural steel will be defined as follows:- Fire type: cellulosic, hydrocarbon or jet fire- Fire duration: minutes or hours- Critical core temperature: typically between 400°C and600°C for structural steel members- Unexposed (non-fire side) temperature: for divisions:typically 140°CFigure 2 shows the result of a typical simulation. Thecoatings used in this simulation were successful in delayingattainment of the critical level.Responsible specifiers and contractors only use productsfrom manufacturers that are independently tested to thestandards mentioned above. Of course, as with any certifiedproduct, the specifier should seek further details on the levelof certification or additional certification which somearchitects or designers use such as UL263 exterior listing,approval for use in ISO 12944 environments or explosiontesting to 4 bar overpressure. Furthermore, PFP for use in

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buildings should have some level of hydrocarbon fireresistance (UL1709 Design XR627).

Thin or thick filmsThere are a wide range of PFP products available, includingintumescent coatings and cement and fibre-based products,as both spray products and panels. Intumescent coatingsare paints which react to form a thick char when exposed toa fire (Figure 3).To combat these different fire loads, PFP products can besplit into two categories:- Category 1 - Cellulosic fire protection developed for use oncivil construction and infrastructure projects. Intumescentcoatings for this category are generally known as "thin film",with application thicknesses typically up to about 1mm. Thematerial swells rapidly (intumesces) to up to 60 times theoriginal thickness when exposed to fire.- Category 2 - Hydrocarbon, jet and rapid rise fire protectiondeveloped for high risk environments such as oil rigs andrefineries. Intumescent coatings for this category are oftenlabeled "thick film", with their thickness measured inmillimetres rather than microns. The required coating can beanything from 3 to 20 mm thick, depending on the desiredlevel of fire resistance.

Off-site application of cellulosic PFP preferredTraditionally, intumescent coatings have been applied onsite, but more recently, products have been developedwhich allow application off site or in shop.The NIST recommends the development of criteria, testmethods, and standards, firstly, for the in-serviceperformance of sprayed fire-resistive material used toprotect structural components and secondly to ensure thatthese materials, as installed, conform to test conditions usedto establish the fire resistance rating of componentsassemblies, and systems. Consequently, offsite applicationensures a result, which is consistent and to specification.The main advantage of applying PFP offsite is that structuralsteel arrives at the place of use already fire protected.Should there be any fires on site before erection is fullycomplete, the steel will be fully protected. In many cases,when using a single coatings supplier, the steel should alsoarrive fully protected with a high performance PFP and paintsystem.The application of PFP offsite also greatly reducescomplexity of a project by decreasing the number of workerspresent on site, helping with scheduling. Other advantagesare:- Reduced cost- Steel is protected by companies operating in the most costeffective locations rather than conditions dictated by the site.- Easy access and large application areas lead to increasedefficiency.- Reduced equipment and scaffold requirements on site.- No need to seal off areas during application or masksensitive equipment.- Improved Quality Control- Controlled application conditions and auditable qualitycontrol procedures ensure that the correct thickness of PFPis applied.- Greater control over application techniques.- No access issues.- Environmental and Health & Safety impact reduced- With less people on the construction site the chance ofaccidents is reduced.- By eliminating the intumescent paint system on site thereis a reduced chance of spills and fire.- The steel is at ground level, therefore there are no accessissues.

Performance testing is essentialPassive Fire Protection manufacturers have to carry outextensive testing to demonstrate their products' propertiesby ensuring the coatings are correctly evaluated andmeaningful performance data is established. Fire testing isessential to make sure that any PFP material specified orused meets the required performance standards for thestructure set by national or international, legislation.In addition to their fire resistance, products are tested forsuitability for use in different environments and for theirability not to deteriorate over time. To make sure the productsold matches the performance of the original, fire-testedmaterial, recognised test establishments offer follow-upservices to monitor factory quality control and undertakerandom product sampling and verification.By testing for any changes which may contradict theiroriginal certification of a product, these establishmentsensure that the performance claims of PFP product continueto match actual performance in the field. However, it is worthnoting that not all manufacturers subscribe to this service. Ahigh quality PFP manufacturer will provide the user orspecifier with:- the correct PFP product for the fire type scenario.- Recognised approvals.- An approved follow-up service.To meet these demands, Akzo Nobel's International Painthas developed a series of shop applicable intumescent PFPcoatings which have recognised approvals for cellulosic fires(product name "Interchar") and hydrocarbon fires (productname "Chartek")

Results at a glance- Passive fire protection systems help to overcome thecatastrophic effects from fires in steel-structured buildingsby prolonging their structural integrity and allowing forproper emergency response and evacuation.- The requirements and specifications for PFP coatings arevery demanding.- Proper selection and qualification of a PFP coatingrequires intense cooperation between specifier, contractorand coatings manufacturer.- The coatings manufacturer has to provide both, specifierand contractor, not only with state-of-the-art PFPtechnology, but also with intensive support includingpre-qualification and follow-up services.- Products properties have to meet the requirements ofcurrent trends in PFP application such as shop (off-site)application and increasing esthetic demands of architectsand building owners.

The author:-> Paul Mather is responsible for worldwide productdevelopment and technical support for Akzo Nobel'sInternational Paint fire protection and insulation materials,where he is actively involved with the development of firetesting standards. Over the last 13 years he has written, orco-authored, a number of technical papers and articlesconcerning fire testing and fire protection issues.

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Figure 1: Passive fire protection systems help to overcome the catastrophic effectsfrom fires in steel-structured buildings by prolonging their structural integrity and

allowing for proper emergency response and evacuation.

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Figure 2: In this simulation the uncoated steel would fail in less than 20 minutes,whereas PFP protected steel hinders structural failure for more than 60 minutes.

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Figure 3: In a fire, an intumescent coating reacts to form an insulating char whichprevents rapid heat transfer to the steel structure.

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