When passive fire protection works the victory is silent. Firefighters brag about their trucks and nozzles, but rarely give the fireproofing its due when a critical save happens. But when passive fire protection fails or is absent altogether, history is made.
SEPT. 11, 2001 — Hijacked airplanes crash into the twin towers of the World Trade Center. Although architects considered the possibility of an aircraft impact, they never planned for the accelerating speeds and massive 20,000 gallon fuel load involved. The initial impact blasts most of the spray on mineral-wool fiber fireproofing off the structural steel. Instead of lasting four hours as fireproofing standards require, the steel gives way within 1¾ hours in one tower and only 56 minutes in the other. Miraculously, no more than 2,792 individuals died in the multiple collapses.
NOV. 18, 1996 — An arson fire stops a shuttle train inside the British-French Eurotunnel, resulting in a 12-hour event causing extensive damage. Overhead dampers for ventilating smoke slam shut early on when the rising heat generated by the fire burns out electrical wiring for the electrical actuators responsible for operating the smoke ejectors. Passengers barely escape with their lives and fire fighting efforts are greatly impeded. The next incident is famed as one of the worst blunders in American fire prevention.
JAN. 16, 1967 — An exhibit hall fire consumes the 180,000-square-foot McCormick Place exposition center in Chicago. Standard procedure of the era called for fireproofing the support columns to a height of only 40 feet. With a heavy fire load and no sprinkler system, the flames soon reached the unprotected level. The columns weakened and failed, bringing the roof down.
In industry, missing or inadequate fireproofing can be just as devastating. Millions of dollars may be dependent on whether the leg supports for an LP tank survive the flames or if the valve at an isolation unit continues to operate regardless of fire. Saving lives may hinge on the extra time that fireproofing gives people to react.
T.H. Dearing, president of Houston-based Thermal Designs, Inc., said it is equivalent to buying insurance. “It’s protection against something that you might not be able to conceive would ever happen, but you know you have to be prepared if it ever does,” Dearing said. “Our knowledge of risk teaches us that for protection to be effective, it must be in place and available for service as designed. Experience and history have taught us that the human is the most unreliable variable in the risk equation. The probability of humans under stress to react properly and timely to initiate mitigation measures is rather low even in the best trained organization. Secondly, mechanical systems — such as mitigation systems — can, do and will fail for any number of reasons when they are needed most.”
Passive fireproofing can be categorized into four main types: cementitious, intumescent, fiberous and composites. Dearing, a former plant safety manager and fire chief, said the first attempts at fireproofing in industry came from the simple realization that the size of the fire, and consequently the damage incurred, is proportional to the surface area of the fuel. Isolating the fuel at the source by way of mergency isolation valves in key locations translated into smaller and more controllable fires with less heat load to cause damage.
Fire bricks were used for tower skirts and to protect pipe racks in the 1920s and 1930s. In the 1940s, lightweight concrete came into its own as industrial fireproofing. First, it was applied to stanchions supporting pipe racks. That concept was further carried to other process equipment containing flammable liquids such as desalters in crude still units.
Cementitious fireproofing absorbs and reflects heat by the evaporation of water bound into the material. Heat from a fire evaporates water at the material’s surface without flame inpingement penetrating to the metal to be protected. As the water heats to boiling point it forms steam, which both repels the fire and absorbs heat. The temperature of the heated cement is conducted through the mass to the metal to be protected. A temperature of 400 degrees C is the maximum allowable for carbon steel and determines the PFP.
As fireproofing material, concrete is cheap. However, it is also heavy. To support the additional weight, engineers are forced to use more steel than would otherwise be necessary for structural support. Another drawback is corrosion. Concrete and other cementitious materials such as gunite or magnesium oxychloride react with the metal beneath it. Because these materials are porous, water is absorbed into the fireproofing further contributes to corrosion.
“During World War II it became standard procedure to wrap LP vessels in wire mesh and then apply concrete for passive fire protection,” Dearing said. “These tanks were built with an expected service life of about 50 years. In the 1970s, close metal inspection showed that almost all of the corrosion allowance for the tank metal was gone due to moisture induced metal corrosion. This was particularly prevalent around the nozzles on top, the manways, the process nozzles and where the support legs and tank met. Many companies went ahead and took them out of commission after only 25 or 30 years into their service lives.”
Today it is unusual to find concrete applied to the tank itself. Concrete fireproofing is generally limited to pipe supports and vessel skirts to prevent a structural collapse and loss of product containment during a fire. Rather than rely on structural fireproofing, industry chiefly today use water spray systems, deinventorying systems or inerting systems.
Industrial fireproofing entered a new phase in the mid-1970s. A rash of transportation disasters involving railroad LPG tank cars, Crecent City, LA, and Kingman, AZ, among the worst, made federal regulators keen to find a way to insulate the cars from direct flame impingement. Spray-on fireproofing such as Chartek® and Thermolag® came onto the market. These products sprung from the development of heat resistant materials used for the space program. These products generally fell into the intumescent category.
Again, the fireproofing had drawbacks. LPG railroad cars often change service to be used as anhydrous ammonia carriers in the summer. As part of the preparation, the interiors were steam cleaned. The expansion and contraction of the tank car surface often damaged the exterior fireproofing. Railroad car manufacturers learned they could achieve workable fireproofing by building double walled tanks with fiberglass insulation between.
Another development in the mid-1970s would steer fireproofing in a new direction. OPEC slapped a lid on oil exports to the West, sparking the famous energy crisis. Almost overnight, the price of oil shot up from $2 a barrel to as much as $45. The 1970s would become the last great period for expansion for American refineries with new facilities being built and existing ones upgraded.
“In the early to mid-1970s the philosophy in the hydrocarbon business was considerably different than it is today,” Dearing said. “The preservation of assets, the public exposure, and the litigation environment environment were nowhere near what they are today. That changed almost overnight.”
Most important was finding better protection for critical control systems. A large petroleum fire can reach temperatures in excess of 2,000 degrees F in less than five minutes. The emergency shut-down system that uses remote activated valves is the critical strategy today for response to hydrocarbon and chemical fire. These automated valves are used to divert or stop the flow of flammable liquid. Control of the process during emergencies is the paramount loss control strategy in use today, said Dearing.
Options for fireproofing these controls were limited. Sprinkler systems are subject to explosion damage even before they can be activated. Even if successfully activated, sprinklers do not stop radiant heat or flame inpingment that destroys wiring in cable trays. Flexible bags or blankets and rigid enclosures have been used with varying success. They are difficult to reseal if maintenance on the protected component is necessary, promote corrossion, are hard to access for day-to-day operation, and costly to maintain.
Before the 1970s, most remote control systems for valves and actuators in refineries were pneumatic. When pressure was released the device would open or close as designed. To protect them against fire, a box filled with calcium silicate thermal insulation was built around the device. The box was then wrapped in canvas and completely sealed to access.
“Of course, if you ever had to work on them, which was common, the boilermakers would go in with a hammer, beat the box up and never replace it,” Dearing said. “If you had a fire and someone said ‘Well, I thought we had a fireproof valve actuator but it didn’t work,’ invariably you would find that somebody had destroyed the box.”
Boxes were heavy and took up a lot of valuable plant real estate. Because of the odd shapes and angles involved boxes were difficult to assemble. If that assembly was less than perfect, moisture would cause the insulating material to deteriorate. Removable insulation or blanket type fire protection still had the weight problem and was difficult to interface with today’s more sophisticated process control systems. As with the boxes, blankets and bags were rarely replaced exactly as installed, thereby negating their protection.
With the switch from pneumatic to electronic systems in the 1970s, another problem with fireproofing became apparent. Insulating materials trap heat. While that heat transfer did not affect pneumatic controls, electronics were more sensitive to heat induced electrical component failure. Insulation on electronic wiring breaks down at 220 degrees F. Electronic components such as transistors become unstable at high temperatures and fail. Even without a fire, electronics control valves and actuators were sometimes subject to spurious shutdowns due to heat under normal circumstances.
Some companies began looking at fireproof encasement using epoxy resins as a solution. Thermal Designs, Inc., founded 26 years ago, developed a lightweight PFP system that provided protection in a hydrocarbon fire for up to 30 minutes. The time lag between ignition, discovery and onset of control efforts can allow a small fire to grow quickly. Although the estimated amount of time to react varies from company to company, American Petroleum Institutes standards call for a 15-30 minutes range of endurance for passive fire protection systems.
“I was on the committee that wrote the standard,” Dearing said. “The thought was whenever you have a significant event all you see is fire and smoke. You don’t know what is on fire. You just know that it is burning out there. The way you determine what is on fire is to watch your control instruments. Where am I losing liquid level? Where are my pressures going up? What position are my valves in? What flows need to be blocked?”
Allowing 10 minutes to find the source of the fire and 10 minutes to figure out what to do leaves 10 minutes to actually institute the control command. With some high pressure systems, closing a large, gear-driven valve might take 10 minutes to stop the flow, Dearing said.
Thermal Designs’ initial enclosures used a stainless steel frame and high temperature alumna ceramic fibers manufactured with a patented wet slurry vacuum molding system. Unfortunately, the age old maintenance problem persisted. The enclosures, like their predecessors, were rarely replaced with the same care with which they were originally installed. Following requests from Exxon and Phillips petroleum, and with their cooperation, Thermal Designs, Inc., began a new phase of development to come up with a passive fire protection system that was not only fireproof but people proof.
The company’s first experiments involved hand applying commercially available intumescent epoxy to actuators, the device that physically closes the valves. Moving on to phase two, Thermal Design, Inc., developed their own propriatary formulation of intumescent exposy and an injection mold process in which a two-part polymide cured epoxy containing flame retardant is molded directly onto the individual protected device. A uniform half-inch thickness provides at least 30 minutes of protection and limits the internal temperature increase within the protected system to about 140 degrees F in a 2,000 degree F hydrocarbon fire. All designs are fire tested with the equipment actually operated during the fire tests.
“In the protection of these refineries what you’re trying to do when a fire breaks out is keep the genie in the bottle,” Dearing said. “If you can’t maintain control you’re relegated to fighting the fire with firefighters and sprinkler systems. Once it gets out you’re at the mercy of something you can’t control.”
Thermal Design’s K-MASS® Fireproofing System is a proprietary formulation, epoxy based, intumescent coating. A solid coating, heated by flame, coverts into a highly viscous liquid. At the same time, endothermic reactions release inert gases with low thermal conductivity that are trapped inside the liquid. Reactions between the polymer chains result is a four-to-one expansion of the coating, forming a low density insulating char that absorbs and reflects much of the heat generated by the fire.
“Intumescence is a physical property,” Dearing said. “It causes a material to go through a phase change, so it is giving up energy as it is going from the solid state to gaseous state. Through an expansion of the material heat is reflected away.”
Once the intumescent coating is bonded to the surface of the component, plant personnel, using standard tools, can perform routine maintenance without compromising the fireproofing. There is no additional cost for installation as with blankets or boxes.
After servicing, the actuator is reassembled, and the fireproofing is automatically in place. Since it is molded to the shape of the original device, no great amount of space is taken up.
To guarantee performance, Thermal Designs tests its design for each brand, model and size of actuator and valve under load.
“There is no way to tell if it works unless it is tested, so when we build a design we fire test it in a controlled environment,” Dearing said. “Furnace temperature and internal temperature are monitored and we check the device under load. In a 25 minute test, the device is checked every five minutes. In the last five minutes of the test, which is the most severe part of the operation, it is checked once every minute.”
The coating is durable, weather-resistant and corrosion-resistant. It does not absorb moisture and is unaffected by most chemical processes. The only recommended maintenance is repainting the exterior every three to five years. Intumescent coatings are not invulnerable, however.
“Epoxy is very tough material,” Dearing said. “We make automobiles, boats, even armor plating out of it. But as with any hard material if you spread it over a large surface area it is susceptible to shocks or impacts. The typical use of chain swings or setting it down hard and causing a vibration
can make it crack. I won’t say it has to be handled gingerly, but it does have to be handled with caution to prevent damaging the epoxy base.”
Epoxy enclosed devices have provided a solution to at least one of the three historic fireproofing failures noted earlier. After the Eurotunnel fire, K-MASS was used to protect all the actuators controlling the smoke ejection system. The epoxy material has also found its way into use in the London Underground and other subway systems. Thermal Designs counts such major petroleum companies as Exxon-Mobil and Phillips among its customers.
K-MASS is also used by the U.S., U.K. and Spanish navies to address shipboard fire hazards. Regardless of what fireproofing system a company chooses, some basic questions must always be addressed, Dearing said.
“Whatever you’re trying to protect, the key questions to ask are how much temperature will it withstand over a period of time in order for you to safely shut the process down, evacuate the people and allow others to institute emergency operations without endangering life.”