Bernie Padgett knew a lot about construction. In 15 years as an electrical engineer in the Chicago area, he’d worked on major projects for NBC, the Chicago Sun-Times and Daily News, Marshall Field’s, O’Hare International Airport and the local subway system. The general contracting firm he founded in 1964, Werner-Herbison-Padgett (WHP), built warehouses and sporting facilities, among other structures, and served clients both domestically and internationally. By 1980 the company had a federal contract to provide specialized military-grade metal building systems across the U.S.
Those buildings, made of steel and exceptionally durable, proved useful for another purpose as well: training towers for the fire service. WHP built its first one that year when the fire department in tiny Kotzebue, Alaska needed a structure that could withstand the snow, ice and wind of its ferocious Arctic winters. For WHP that was easy enough, but the department also had another request: a burn room for regular live-fire training.
Such a room would need a liner to protect the exterior structure. This sent Padgett in search of heat-resistant materials he might leverage for such protection, and he found a solution in the world of smelting steel. The furnaces used for that had refractory interior linings made of brick or castable and exterior shells made of steel — and between them, they used calcium-silicate as an insulating layer.
An effective insulator, calcium-silicate slowed heat movement through the refractory lining, reducing energy loss, keeping external temperatures down and protecting other components. Insulation using it emerged in the mid-20th century, formed by steam-curing lime and a silica source like diatomite. By the 1970s it was widely available in rigid, asbestos-free boards that were stable, noncombustible, low-conductivity and could survive extreme temperatures.
Facing the same core problem as the steel smelters — exposing one side of a structure to extreme heat while preventing that heat from damaging the structural material behind it — Padgett used calcium-silicate as a basis to create Padgenite, a proprietary product WHP used in panels to protect its burn rooms. Its first incarnation, Padgenite I, was the first high-temperature, thermal insulating burn room panel created specifically for firefighter training.
“It was a new application at the time, although other industries used calcium-silicate in different designs,” said Megan Kirchner, marketing manager at WHP Trainingtowers, the prominent provider of metal fire training structures WHP grew into. “We’ve evolved the design of the product to be what we believe is the best available use of it.”
The gold standard in thermal lining
Today’s product is Padgenite Interlock, an improved version that bolstered panel density and durability to withstand impacts, abrasion and hose streams. It’s a unique and essential component of WHP Trainingtowers’ metal fire training facilities.
“Calcium-silicate is really the gold standard — it’s the tried and tested thermal lining material in the industry and can come in a lot of shapes and sizes and densities,” said Joe Kirchner, the company’s chief operating officer. “The unique aspect of Padgenite is that we put it through a special machining and waterproofing process, which is part of its patent, that creates a product that is both strong and stable enough for high heat environments, as well as durable enough for the fire service. The calcium-silicate technology was borrowed from the furnace lining industry, but furnaces don’t get beaten up by firefighters, so we had to make sure we were designing a durable product.”
Durable its structures are — that first Alaska training tower built in 1980 is still working. Padgenite’s protection is a big part of that. Today it’s added to burn rooms by way of the company’s patented Padgenite Interlock tile system. Tiles are 15 inches square by an inch thick and withstand sustained temperatures of up to 1,700 degrees Fahrenheit and maximum temperatures of up to 2,000.
It’s a tile size the company has worked to optimize. Shrinking the panels from earlier configurations reduced the distance between supports, leaving each tile with less room to flex when struck. Combined with a harder surface and interlocking mounting grid, that greatly improved resistance to impact-driven cracking. “It basically doubled our impact resistance,” Joe Kirchner noted.
The tiles’ key interlocking component comes from lapped edges that overlap within their thickness, leaving their faces flush. Simple butt joints would leave straight seams through which heat and hot gases could reach the mounting system and substrate, but lapped joints create an offset, indirect path that’s a better thermal barrier. The tile system also incorporates expansion and contraction joints so tiles can move independently during rapid heating and cooling and be easily removed for inspection.
Tiles are pinned in place, rather than drilled or screwed, to support that. Behind them are offset mounting channels — essentially metal furring members fastened in a grid to the burn room’s walls and ceiling. These hold the Padgenite tiles 1½–3 inches away, creating a cavity behind the liner for additional thermal protection. Bolts and washers at tile intersections clamp the tiles to the grid without penetrating the tiles, and thermal washers decouple the exposed mounting components from the structure.
When this system was exposed to interior temperatures of 1,000 degrees Fahrenheit, company testing found, the temperature reaching the exterior structure was 334 degrees with a 1½-inch gap and 238 degrees with a three-inch gap.
Extreme heat is the biggest part of protecting burn rooms, but the constant application of water in powerful hose streams is a factor too. For that Padgenite tiles use a factory-treated waterproofing polymer that resists mold growth and doesn’t require drying out between uses.
Rooms lined by Padgenite tiles can accommodate Class A combustion fires as well as Class B props. At a mean temperature of 800 degrees Fahrenheit, the tiles maintain a K factor — a measure of heat conduction — of 1.465, meaning they conduct heat around 200 times less readily than the surrounding steel. Padgenite tiles are also asbestos-free and can be retrofit into any noncombustible existing facility.
“The version of calcium-silicate we found provides the best balance between surface hardness and weight, so people can retrofit into existing structures without adding too much weight,” said Joe Kirchner. “There are a lot of elements that we’ve designed into this tile to optimize it for fire training.”
What goes into a burn room?
NFPA 1400, the recently consolidated standard on fire service training, now encompasses the former NFPA 1402 on facility requirements and NFPA 1403 on live-fire operating requirements. Functionally it requires burn rooms to be managed as life-safety systems. Specific requirements include testing and inspection before live-fire use and during each day of gas-fired operation, as well as after unusual damage or overheating. Structural inspections are required annually, and additional inspections every three years for structures with calcium aluminate refractory concrete, every five years for Class A-fuel structures and every 10 for gas-prop structures.
For a Padgenite-lined room, a practical pre-use inspection would look for cracked or displaced tiles, open joints, loose fasteners or exposed mounting channels. The stability of the calcium-silicate used in the product means damage will be rare and minimal, but cracking or a displaced liner may mean taking a room briefly out of service for a quick exchange.
“It’s a pretty simple thing to maintain,” said Joe Kirchner. “The expansion and contraction are minimal, so you’re not getting a lot of wear and tear on those components. But per NFPA 1400, you want to check your fastener systems, make sure they’re in place, and if there’s any impact damage, make sure it’s addressed prior to burning.”
WHP Trainingtowers can assist with NFPA compliance inspections for both its fire-training facilities and others, including steel, concrete, concrete-masonry and container-based structures. This includes an on-site evaluation by a licensed structural engineer; examination of structural components, walls, roofs, doors, windows, etc.; inspection of thermal linings, mounting systems and fasteners; removal of sample lining panels to check underneath; a written report with findings and recommendations; and an on-site debriefing.
In developing a burn room, departments should look at the actual fire scenarios they encounter and start with a room of representative size.
“We recommend a minimum burn room size of 12 by 12, which is your average-size bedroom,” Joe Kirchner said. “We also recommend multiple entry points to that room so you can put the seat of the fire in different areas and attack it from different openings.”
Keeping it on the first floor of the training structure (WHP Trainingtowers offers both fixed and modular structures that are highly configurable) lets firefighters stage on the second floor and move downstairs to simulate an attack below grade. Adding another on a higher level supports training for an upstairs attack.
For more information, visit WHP Trainingtowers.
Padgenite is a trademark of WHP Trainingtowers. WHP and WHP Trainingtowers are registered trademarks of WHP Trainingtowers.
