Author(s): Jesse Roman. Published on September 4, 2014.

A CONSTRUCTION WORKER BECKONS ME. “Want to see something amazing?” he asks.

Considering our present location—the north tower of St. Patrick’s Cathedral, 10 stories above Manhattan’s bustling 5th Avenue—I’m prepared for anything. He motions for me to follow him through a narrow hallway and up a short ramp. He stops at a large rectangular opening in the cathedral’s stone wall and gazes out. Just beyond the opening, a narrow wooden plank hangs off the outside of the spire.

He tells me it’s where he often goes to sit while on break, perched among the cathedral’s stone finials with Manhattan stretched out before him. “It’s the best place in the world to eat lunch,” he says, his plump face grinning below a high-fitting hard hat.

But it isn’t the spectacular dining vistas, or even the cathedral’s newly gleaming marble or vivid stained glass, that I’ve come to see—it’s the dusty attic.

About 50 feet from my new friend’s lunchtime perch, in this once-hollow tower, sits the newly constructed mechanical room of the cathedral’s state-of-the-art water mist fire protection system. Essentially a 170-square-foot concrete box, the room houses 24 red nitrogen gas canisters, each one about five feet tall; a 1,000-gallon metal water tank; and gleaming thickets of pipes, valves, and levers. From here, stainless steel piping passes through the tower’s six-foot-thick brick supporting wall, then fans out across the cathedral’s 33,000-square-foot attic, which covers almost all of the historic structure’s footprint. 
 

The Evolution of Mist

Even as the codes don’t regard mist as effective as traditional sprinkler systems in controlling or suppressing fires, alternative applications are growing

Like some theories of evolution, water mist technology moved from sea to land. The first applications for mist were in enclosed compartments aboard ships, and then throughout cruise ships in common areas such as shops and restaurants. Because water mist uses up to 90 percent less water than sprinklers, the technology allowed boats to travel lighter without taking on heavy and destabilizing loads of water.

Read more about the evolution of mist

The installation of the water mist system is part of a monumental $177 million restoration project, the largest in the cathedral’s 135-year history. For the last two years, as many as 200 workers per day have swarmed every far-flung corner of the cathedral, inside and out, erecting scaffolding, cleaning stone, restoring bronze doors and stained-glass windows, installing new heating and cooling systems, and more. Workers began installing the water mist system in March 2013, using NFPA 750, Water Mist Fire Protection Systems, and relying in large part on the guidelines provided by the manufacturer, Marioff Corporation. The system received mechanical sign-off from the Fire Department of the City of New York (FDNY) in November 2013.

“NFPA 750 says you must live and die by the manufacturer’s DIOM [design, installation, operation and maintenance] manual,” says Tom Newbold, a principal at Landmark Facilities Group, the engineering consultants who helped design the cathedral’s water mist system. “We relied on NFPA 750, and
NFPA 13, Installation of Automatic Sprinkler Systems, came into it to some degree. And then the Marioff DIOM manual.”

The water mist system cost about $1.1 million, roughly $350,000 more than if the cathedral had installed a traditional sprinkler system, according to Structure Tone, Inc., the firm handling construction management of the restoration. According to Newbold, the only other suppression system in the cathedral is located in a small basement area, which is protected with sprinklers. A neighboring rectory, which is physically connected to but technically separate from, the cathedral has a full wet pipe sprinkler system that was added when the structure was renovated about four years ago. So far, cathedral officials say, St. Patrick’s has escaped any significant fire events since opening its doors.

For decades, cathedral officials had resisted installing a fire suppression system in the attic space, fearing the effects of water on the historic structure—though as fire officials point out, the impact of a sprinkler system on the cathedral would be significantly less than a fire or the quantity of water used during firefighting operations. Working with the FDNY, along with sprinkler designers and installers, cathedral officials arrived at a solution that they believe provides an acceptable level of fire protection while accommodating the unique structural requirements of a venerable cultural landmark.

“There were a lot of engineering challenges, not only from the mechanical side but from the structural side as well,” says Structure Tone’s Ron Pennella, project manager and one of my tour guides for an up-close look at the system. “There’s no other system like this in the country.”

“A box of tinder”

Covering an entire square block in midtown Manhattan, St. Patrick’s is the largest Neo-Gothic-style Roman Catholic cathedral in the United States, with spires rising 330 feet above the street and pews that can hold up to 2,400 worshippers. Construction began in 1858, and the cathedral opened in 1879. It has hosted a pope, been the site of notable memorials and funerals—from Babe Ruth and Vince Lombardi to Robert F. Kennedy and Andy Warhol, to name a few—and has long been a preferred wedding venue of New York’s social elite. It is also one of the city’s most iconic tourist landmarks, drawing more than 5.5 million visitors each year, according to stpatrickscathedral.org.

In 2012, the cathedral announced the launch of an ambitious three-year restoration project that would include repair and cleaning of its marble exterior, cleaning of its stained glass windows, systems upgrades, and more. When I arrive at the cathedral on a Monday morning in July, the extent of the work is apparent: much of the outside is covered in scaffolding. Inside, the stark contrast of the soaring and elegant Gothic columns wrapped in an industrial cage of scaffolding is surreal. Workers clad in hard hats, safety vests, and boots haul heavy rope past kneeling worshippers deep in prayer. Other workers scramble over the scaffolding as a priest’s booming voice welcomes visitors to mass.

Along with Pennella, my guides for the tour of the new water mist system include Newbold, as well as Kate Monaghan, assistant communications director for the Archdiocese of New York. We gather just inside the cathedral’s 5th Avenue entrance, and Pennella leads us through a nondescript doorway to begin a dizzying ascent up a series of winding staircases. We eventually arrive at a small, window-filled landing halfway up the cathedral’s south tower. For generations, New York City firefighters have assembled here to train for the possibility of fire in the bone-dry attic. Evidence of their presence is seen on the tall, narrow windows surrounding the landing. Dozens of names and dates are traced with fingertips in the dust and permanently baked in by the sun. A few names date to the 19th century, just after the cathedral opened; four belong to firefighters who died in the 9/11 terrorist attacks. 

Culture Codes
A primer on NFPA’s cultural and historical occupancies codes

NFPA 909, Protection of Cultural Resource Properties—Museums, Libraries, and Places of Worship, and NFPA 914, Fire Protection of Historic Structures, are purpose built to address the exact types of challenges found in the St. Patrick’s Cathedral project. “Each code is set up to provide a path forward in terms of finding the right type of protection measure for the circumstance,” says Gregory Harrington, staff liaison for the NFPA Technical Committee on Cultural Resources, which maintains both codes.

Read more about culture codes

The landing is at the same height as the cathedral ceiling and is the point where the tower shoots skyward beyond the main building. We leave the spiral staircase, which continues up the tower, and walk down a short passageway, where a ladder brings us to the attic. The cavernous space, which smells of stale wood and must, sits just above the cathedral’s famously ornate ceiling. Ironically, between the low light, Pennella’s hard hat, and the aluminum trolley system that was built to help install the water mist system, I have the sense that I’ve entered an old mine shaft, not a cathedral attic 110 feet above the street.

Looking up from the sanctuary below, it appears as if the ceiling is assembled of the pale Tuckahoe marble used elsewhere in the cathedral. But the attic catwalk offers a different vantage; the ceiling isn’t marble at all. “St. Patrick’s was built during the Civil War, which, as you can imagine, was not a great time to build a cathedral,” Monaghan says. “To save money, the ceiling is constructed from a wooden frame, covered in wire mesh and plaster. The plaster is painted to look like marble.”

As a result, the attic is “a box of tinder,” says Newbold, who’s also a volunteer firefighter in Trumbull, Connecticut. “It’s comprised of major truss timbers and a ton of little pieces of wood that are used to hold up the plaster—I call those kindling.”

The FDNY had advocated for years that St. Patrick’s install a fire sprinkler system in the attic space, but the cathedral had resisted. Activation of a single automatic sprinkler may discharge 15 to 20 gallons of water per minute, and cathedral officials feared that the weight of that accumulated water, about 8.3 pounds per gallon, could potentially overwhelm the fragile ceiling.

“It would fall to the ground,” Monaghan says. “That has always been a unique challenge at St. Patrick’s. That’s the basic reason we chose a water mist system.” With many other large-scale improvements also planned and a fundraising campaign underway, cathedral officials decided that now was the time to address the potentially catastrophic fire hazard in the attic.

Newbold and his team designed a system of 246 water mist nozzles arranged into eight zones and three height levels to blanket the attic space from the eves to the floor. Stainless steel pipes emerge from the mechanical room in the north tower and stretch out in precise lines in every direction. Nodes branch off and terminate in compact nozzles barely perceptible amongst the attic’s enormous beams and supports.

In the event of a fire, the nozzles closest to the fire would activate, discharging the pressurized air from the steel lines. A mix of water and nitrogen, originating in the mechanical room, would shoot through the pipes under a pressure of more than 1,000 psi—more than 10 times the pressure of a conventional sprinkler system—and out of tiny holes in the water mist nozzle. The result would be a thick fog intended to extinguish the fire by extracting its heat, displacing the oxygen that feeds it, and blocking radiant heat. According to Marioff, the system’s manufacturer, the cathedral’s mist system uses 3.3 gallons of water per nozzle per minute, and the tiny water droplets evaporate or disperse instead of pooling. The mechanical room contains enough gas and water for all the nozzles in one zone to run for about 30 minutes.

To ensure reliability, Marioff’s installation manual mandates that the water and gas tanks that supply the system be essentially at the same height as the water mist nozzles—thus the specially built mechanical room high in the north tower. But locating that room 115 feet off the ground presented numerous challenges, including figuring out a viable way to swap out nitrogen tanks and other equipment. To help solve that problem, engineers used an existing elevator, which runs 35 feet from the ground floor to a choir loft. To get equipment the rest of the way up, workers installed an electrically powered hoist system, which runs about 80 feet up to the mechanical room.

Another addition meant to lessen the impact of the room’s height was an innovative use of the cathedral’s security camera system. “Part of NFPA 750 says there needs to be a monitoring system to check the tanks and water levels on a regular basis,” Newbold says. “The cathedral already has a closed-circuit system, so we placed cameras in the mechanical room pointed at different things so the security guy can visually check in on the system without having to leave his office.”

As we walk across the attic’s catwalk, Pennella and Newbold point out some of the additional challenges they faced in retrofitting the water mist system into a 19th century space. Engineers needed a way to reach the eaves and other remote areas of the attic to install the pipes and water mist nozzles safely and efficiently without damaging the floor below. The solution involved constructing a permanent lightweight aluminum rolling trolley system over the existing catwalk. The trolley is manually operated; a worker climbs into the car and pulls himself along the track using the trolley system’s railing. The trolley has been left in place to help maintain the water mist system.

As for the actual work of installing the stainless steel piping, Pennella likens the process to “shoe-horning your foot into a really tight shoe.” Nineteenth century carpenters built a wooden catwalk so workers could get around the space without stepping on the delicate ceiling below. The catwalk’s various supports aren’t particularly precise, though, Pennella tells me, which made it a challenge to comply with Marioff’s requirements that the nozzles be spaced just so in order to remain effective and unobstructed. As a result, installers found themselves adjusting on the fly when the design drawings didn’t match up with the reality of the building.

“We took some liberties in terms of making it work within the space, because the drawings are bigger than the space we had to work with,” Pennella says.

Installing a water mist system can also be more labor-intensive than a traditional sprinkler system, an important factor in why water mist systems can be more expensive than traditional sprinkler systems, according to contractors. Everything is mechanical, nothing is welded—it’s all wrenched by hand, Newbold tells me, pointing to a row of thick bolts. “All the fittings, because they operate at 1,000 psi, have to be compression fittings, which requires a tremendous amount of labor in assembly,” he says. “You have to make sure everything is tight. All the bends need to be precise.”

The result “is beautiful—it’s like artwork,” Newbold says. “It’s a shame it’s up in the attic where nobody can see it.”

Working with the fire department

For the FDNY, though, just knowing the system is there represents a significant step forward.

Dry standpipes were installed at the attic level several years ago, which would theoretically provide a water source for firefighters. By the time hoses and equipment could be lugged up the spiral steps during a fire event, however, it would likely be too late to mount an effective attack on an attic fire, say fire officials. “Our best estimate is it would probably take somewhere between 20 and 30 minutes before we could get water on the fire if it was up in that area,” says Michael Myers, the battalion chief for FDNY’s Battalion 9.

It would also be difficult to access the building with ladders from the ground, according to Pennella, who has worked closely with FDNY on the water mist system installation. “It's about 140 feet to the ridge beam of the roof, and it's also set back from the street,” he says. “So the fire department doesn’t have any equipment that could physically get in there and fight the fire. So they would employ what they call ‘surround and drown.’ They would try to arc water into the building.”

Church Fires
Recent report finds sprinklers present in only 12 percent of fires involving religious properties

In 1863, five years after the cornerstone was laid for St. Patrick’s Cathedral in New York City, the largest fire disaster in terms of lives lost struck another church more than 5,000 miles to the south, in Santiago, Chile.

Read more about church fires

Faced with less-than-ideal options for fighting a fire at the cathedral, the FDNY has pushed for years for some kind of fire suppression system in the cathedral’s attic—“every chance my predecessors and I have gotten, probably over the last 100 years,” Myers says. “Everybody's been asking St. Patrick's about this and touting the importance of having [a fire suppression system]. But because of the artwork and everything that's here, obviously they were very selective in what they wanted to choose. But yeah, it's been a major concern for our department for a long time.”

As pleased as Myers is about finally having some kind of fire protection in the St. Patrick’s attic, it’s clear he’s also reserving judgment on the water mist system. He admits that neither he nor many of his FDNY colleagues has encountered such a system in a building before.

“On paper it seems like it works, but no one knows exactly how it would react [in a fire],” he says. “We can look at tests, we can look at what Marioff has offered us as far as their testing and what they've done with it, but until we actually fight a fire where one of these systems is in use, it's hard to tell exactly what will happen with it.”

FDNY was actively involved in the design and installation process at St. Patrick’s. Design teams and Marioff reps met often with the FDNY Technical Management team, and also had several walkthroughs with local fire officials. Marioff is also in the early stages of producing a St. Patrick’s-specific training video for FDNY, so companies responding to a fire there will have some knowledge of the system and how it operates.

“This is a high-profile job,” says Marioff’s Adam Tracy. “This technology is new in the city, and FDNY has a vested interest in understanding how this system works.”

Discussions with the fire department resulted in at least one design change, which Pennella shows me back at the landing of the south tower. The easiest way to access the attic is up the spiral staircases in the south tower. Because the mechanical room is in the north tower—across the attic and in the neighboring tower of the cathedral’s imposing facade—the fire department requested that a remote shutoff be installed at the south tower landing; if access to the mechanical room in the north tower was blocked, firefighters could still shut off the system if needed. The remote shutoff option, however, was not in the Marioff design, nor in the installation guidelines or operation manual, so designers were required to send the system out to be tested and approved, at a cost of $20,000, before it could be installed, Pennella says.

“There were incremental costs to give the fire department what they wanted, but it was in the fire department's best interest to have these things,” Pennella says.

That statement could apply to the whole project. “This is one of New York City's landmark buildings, obviously, and one of our most famous buildings,” says Myers, the FDNY battalion chief. “I really do think that this system has been designed well. All the work that’s been put into it is pretty incredible.” 

Jesse Roman is staff writer for NFPA Journal.

 

In This Section
  • Church Fires Recent report finds sprinklers present in only 12 percent of fires involving religious properties.
  • Culture Codes A primer on NFPA’s cultural and historical occupancies codes
  • The Evolution of Mist Even as the codes don’t regard mist as effective as traditional sprinkler systems in controlling or suppressing fires, alternative applications are growing