Specialty Coatings for Fire Safety
Following the collapse of WTC on Sep 11, 2001, there has been considerable attention in building design concept from safety angle. Fire protection has been accepted as a critical aspect of public and commercial building design for decades and there is an urgent need to ensure that adequate fire protection is incorporated and maintained in buildings where large numbers of people might be present. Fire resistant coatings are a relatively new option available to architects. They can help lengthen the time that structural materials can maintain their integrity under fire conditions.
Fireproofing is recognized to play a crucial role in establishing building safety and generally refers to the protection of the structural steel and other supporting members in a building. Traditional fireproofing materials include concrete encasement, gypsum wallboard and coatings categorized as Spray Applied Fire
Resistive Materials (SFRMs) that are typically composed of ingredients such as mineral wool, cement and gypsum and can vary in density. Intumescent fire resistive coatings are newer fireproofing materials. They are paint-like coatings that are applied to structural steel members at a final thickness of from 0.03 to 0.50 inches.
All of these fire proofing materials are designed to provide an insulating barrier between a fire and the structural steel. The barrier prevents the high temperatures within a fire from affecting the structural performance of the steel members. Because the Intumescent coatings have paint-like properties, they are receiving increasing attention from architects and designers.
According to an upcoming study by the consulting firm Kusumgar, Nerlfi, & Growney, global consumption of coatings in 2012 was projected to come in at 67 billion pounds worth $120 billion. Volume bounced back from the recession year of 2009 with the Asia-Pacific region leading the way. However, growth in 2012 slowed owing to global and local economic uncertainties. Coating volume in 2012 is up 15 percent since the 2009 global recession but coating value is up by about one-third largely because of the escalation in raw material prices. The Asia-Pacific Region is the largest consumer of coatings taking 42 percent of the volume in 2012. China accounts for over one-half of the region’s consumption with growth now moderating from the rapid expansion of the past. India is now about 15 percent of the regional volume and continues to increase its share. Europe is the second largest market for coatings taking 27 percent of the global volume in 2012. Consumption in 2012 was hurt by the region’s economic crisis. North America was an outlet for one-fifth of the global coating volume and has mature growth prospects. The South and Central America region was eight percent of the global demand in 2012. Growth in the region slowed in 2012 but is forecast to grow modestly in the future.
Fire Retardant vs. Fire Resistant
There are actually two types of coatings on the market that are designed for use on different substrates and that respond very differently when exposed to fire.
Fire retardant
paints are applied to combustible materials (wood, plastic, foam) and are designed to reduce the rate of flame spread. Typically they are based on silicone, casein or vinyl resins. They look like paints and are formulated to be applied like paints (brush, roller or spray). They do burn, can generate smoke, do not have high temperature resistance and would vaporize under test conditions designed for fire resistant coatings.
The standard ASTM test for flame retardant paints is ASTM E84, which lasts for several minutes. The test evaluates flame spread and smoke development. Coatings that are meant to protect combustible substances are tested over Douglas Fir and are classified as either Class A (Flame Spread under 25, Smoke below 450), Class B (Flame Spread between 26 and 75, Smoke below 450), or Class C (Flame Spread between 76 and 200, Smoke below 450). These figures are indices when compared to Red oak (Flame Spread =100) and Cement board (Flame Spread =0).
Many fire retardant coatings are only rated for the ability to ‘not contribute’ to a fire, i.e. they will not become a fuel source. Others do provide some resistance in keeping the fire from getting to the substrate. Most create a soft char that will not keep plastics from melting and dripping into a fire. Some do not do a good job at keeping rapid heat transfer through metal. Smoke management is another, even more critical (and difficult to address) requirement. The smoke generation due to substrate/coating interaction will be different for different fire retardant paint/substrate combinations and must also be designed into a robust coating system.
Fire resistant
coatings provide insulation to the substrate. Intumescent fire resistant coatings work by expanding their volume from 15 to 30 times and generating an ash-like char layer that erodes as fire exposure continues. Expansion then occurs again, with the number of times the process repeats itself dependent upon the thickness of the coating. The shape of the structural steel will affect expansion and char formation.
These coatings are given fire ratings (1, 2 and 3) depending on the length of time for which they can provide this protection. Adhesion, char integrity and char growth are critical. The standard test for these materials for a cellulosic fire is ASTM E119 (UL 263, NFPA 251, UBC 7-1), which involves placement of the coated part in a furnace for as many as 3-4 hours. UL 1709 is the test used when it is necessary to simulate a hydrocarbon fire, which can reach very high temperatures very quickly (2000ºC within 5 minutes). Fire resistant coatings are much thicker than fire retardant coatings and are either sprayed or towelled on. The rheology of these formulations is designed so that the coating hangs at high film builds.
Building Codes and Appropriate Applications
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Fire protection requirements are established in various building codes. There is no uniformity in these codes. Within the U.S. they are established by individual towns and states. Federal government buildings and military structures have yet different requirements. Outside of the U.S., codes vary from country to country as well. |
This lack of cohesiveness in building codes is a problem for the industry," notes Rick Jones, Vice President of The ChemQuest Group, Inc., a Cincinnati based coatings consulting firm. “A consistent set of fire proofing requirements would make it possible for coatings manufacturers to better focus their R&D efforts on achieving specific physical characteristics for given building scenarios.”
The codes address what types of materials should be used for what substrates and in what sections of buildings. Expected occupancy, height of the building, and other factors are considered when assigning the fire proofing requirements. Intumescent fire resistant coatings are generally required where ever exposed structural steel is present. Typical examples include lobbies of hotels and high rise condominiums, convention centres, atriums, and remodelled warehouses and docks.
Most often, many different types and levels of fireproofing will be required for any one project because there will be different types and levels of substrates and exposure. “Different substrates require the use of different kinds of coatings," stresses Bob Zielinski, Technical Sales and Marketing Director for Flame Control Coatings, LLC.
For combustible surfaces like wood and plastic, the coating needs to be able to reduce the surface burning characteristics of the underlying substrate. For substrates like metal, masonry and drywall which are effectively non-combustible in nature, the coatings need to either not increase the combustibility of the substrate or it needs to insulate the substrate from the heat and extend the amount of time before the substrate starts to lose its physical properties. With substrates like foam, the coating must be formulated to withstand the inherent base properties of the substrate (like having some flexibility) so that the coating will not fracture or leave parts of the substrate unprotected.
Different types of exposure include vibration (elevator shafts or mechanical equipment), air currents, humidity in non-air conditions spaces, concealed locations, and exposed structures are some examples. Intumescent coatings in general are much more expensive than light weight cementitious fireproofing alternatives. As a result, these cement-based products are typically used for any structural surfaces that will be concealed in a building. They are available in varying densities for different applications. According to Paul Greigger, who is responsible for product development and testing of passive fire protection (PFP) coatings at PPG, cementitious material does have water pick-up issue and will degrade (flake off), resulting in loss of adhesion. In addition, the material must be applied on site and often the building must be sealed before the process can take place.
For exposed structural steel, however, the fire resistant coatings are a more attractive alternative because they provide a textured paint-like appearance and are more aesthetically appealing. "Even though these Intumescent coatings are more expensive than traditional fire proofing materials, they broaden the architect's options for artistic expression," states Jim Rippe, title? With Carboline. He adds that for some industries - computer chip manufacturing, for example - where a dust-free environment is critical, fire resistant coatings are much more appropriate than cementitious materials.
Developments in Testing Standards and Codes
There are numerous standards that have been issued by independent and government agencies and laboratories in the U.S., such as ASTM, UL, ANSI, NFPA, UBC and the US Dept of Defence. Additionally, there are many international standards such as IMO, ISO and MPI. “These standards are very detailed and specify performance criteria including; flame spread, resistance to ignition, rate of heat release, total heat release, smoke generation, toxic products of combustion, VOC, adhesion, resistance to water, salt water,
chemicals and gases, resistance to UV, durability, resistance to mould and bacteria, safety to the environment, and many others,” says Sam Gottfried, title?, with No Fire Technologies.
Despite the existence of so many standards, after the 9-11 tragedy, several groups conducted evaluations and initiated programs to develop more extensive standards for fire proofing materials including Intumescent coatings. In May 2002, the Federal Emergency Management Agency (FEMA) published the “World Trade Centre Building Performance Study: Data Collection, Preliminary Observations, and Recommendation” report that stated that “Fireproofing needs to adhere under impact and fire conditions that deform steel members, so that the coatings remain on the steel and provide the intended protection.”
UL is still evaluating a durability testing methodology (UL2431: “Durability of Spray Applied Fire Resistive Materials”) that includes evaluation of coating performance after the coated part has been exposed to various environmental conditions (accelerated aging, elevated humidity, carbon dioxide an sulphur dioxide exposure, salt spray, freezing , simulated rain, etc.). “The idea is to address the issue of adhesion of these specialty coatings, because adhesion is absolutely critical to proper performance,” comments PPG product development and testing specialist Timothy Figore.
There is still, however, a lack of agreement among the players in the market as to what standards should include. “The market is still not sophisticated enough to develop a consensus as to what the physical performance guidelines should be,” asserts Bijou Ganguly, Product Manager of Isolatek’s Industrial Division.
The International Code Council (ICC) recently approved (May 2007) the first comprehensive set of building code changes based on recommendations from the Commerce Department’s National Institute of Standards and Technology (NIST). The recommendations were based on the findings of NIST’s three-year investigation of the collapses of New York City’s World Trade Centre (WTC) towers on Sept. 11, 2001.
Formulations
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The key ingredients of fire suppressant coatings vary depending on the type of coating. In addition to the resin or binder, ablative coatings, or sacrificial coatings designed to reduce the rate of burn, usually contain fire retardant chemicals such as aluminum trihydrate or antimony oxide. Intumescent coatings contain the resin and approximately 15 other ingredients. |
The three key active components are the promoter or catalyst (typically a phosphate salt such as ammonium polyphosphate), a char former (often pentaerythritol) and a blowing agent (usually a melamine derivative).
Fire retardant coatings contain only a fraction of the amount of some of the ingredients found in fire resistant coatings. "It is difficult to maintain traditional paint characteristics when adding larger quantities of flame retardant chemicals into a formulation," notes Ganguly. "In particular, if too much retardant, generally a phosphate, is used, blending and spraying equipment can become clogged." The use of activated carbon particles is being investigated, but this material is a challenge to keep in suspension.
In general, Intumescent coatings differ in how the fire retardant chemical is formulated to create char growth. “All of the ingredients are important because they interact with one another to achieve the desired overall performance.
For fire resistant coatings, selecting the appropriate resin for a given formulation and application is critical.
"The resin is directly related to adhesion ability and therefore to durability," says Rippe. "In addition, different resins react at different temperatures, and the right resin must be chosen so that the right char is produced at the right time."
There are two main types of resins used in these Intumescent coatings - vinyl acrylics and epoxies. Waterborne (latex) vinyl acrylic formulations are typically used for interior applications. Because the ingredients have some water solubility, the water resistance and general exterior durability of these formulations is affected. Solvent based vinyl resins and 100% solids epoxies find use in external applications where weathering can occur. Epoxies in particular are finding use in offshore oil platforms and petrochemical facilities where there is a potential for hydrocarbon fires and weathering can be a significant issue.
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Formulations of each type of coating may also vary according to the substrate on which they are intended to be used. "Changing of formulations for different substrates may or may not be required and is determined by performance," comments W. Casey West, owner of Albi Manufacturing, a Division of StanChem Inc. "Some coatings are designed to work on multiple substrates, while others may require changes."
The challenge today is to create higher performing flame retardant and resistant coatings that behave more and more like traditional paint with regard to appearance and application. "There are three main properties that need to be addressed," states Don Le, product manager with PPG. "Fire suppressant coatings must be cost effective, provide the expected level of performance with regard to fire protection and durability, and be easy to apply. All three of these characteristics need to be optimized."
Currently the market is looking for interior fire protective coatings that are single component products that can be applied with a bush, roller, or can be sprayed on, and that have the appearance of regular paint. Newer latex paints are coming closer to meeting these expectations. Exterior formulations, however, tend to be much thicker and often are two component formulations that provide a more textured appearance.
Intensive research efforts within the industry are focused on developing exterior formulations that are more paint-like yet retain the performance characteristics of current products. Developing coatings that have the durability of epoxies but the cost of cementitious materials is another area targeted by coatings manufacturers.
Regulatory Issues
Regulations covering volatile organic compounds do apply to fire protection coatings, but they have not up to this point affected the ability of coatings manufacturers to formulate solvent based coatings. “The regulations are performance driven and are not affecting our ability to develop new formulations,” says Rippe. Jones adds that the VOC regulations are based on best available technology and recognize that the performance of the coatings is critical safety issue. Even so, it can be expected that VOC limits will be lowered as technology becomes available to provide the necessary level of fire protection at lower VOC levels. Many manufacturers are shifting to water based formulations already and are working to overcome some difficulties presented by the use of water as the carrier. “It can be a challenge to incorporate the amount of flame retardants necessary to achieve desired ratings into water based (or very low VOC) systems and still maintain the physical properties required for the coating,” notes Zielinski.
For PPG, a greater challenge in developing new formulations of fire protective coatings relates to the numerous different registration lists that currently must be complied with. The U.S., Canada, Europe, Japan, Korea, China and the Philippines all have specific regulatory requirements regarding raw materials. “When developing new formulations, it is a real challenge to ensure that all materials meet the various requirements of these lists from different countries and regions of the world,” explains Greigger.
Reference: Report from Kusumgar, Nerlfi & Growney