Dozens of owners of Marco Polo apartments, where three people died recently in a fire that swept through the building, have secondary hallway doors with louvers that boost air circulation into their units but also can help a fire spread more quickly, residents and fire experts say.

Propping open a main, fire-resistant door so more air can circulate into the units from the enclosed hallways through louvered or screened doors is common at old Oahu high-rises, residents say.

But the practice violates Hawaii’s fire code, according to the Honolulu Fire Department and fire prevention experts.

Using a louvered or screened door to boost ventilation while the main door is propped open undermines the fire door’s purpose, which is to contain a blaze from breaking through that barrier for a set length of time, according to the experts.

Not having sprinklers, as is the case at the 36-story Marco Polo and roughly 300 other residential high-rises on Oahu, would only add to the risk, they said.

“You’re creating easy avenues for a fire to spread,” said Sam Dannaway, vice president of fire protection technology for Coffman Engineers.

Enhancing air flow in such a fashion “would defeat the purpose of the fire door,” added Richard Soo, a retired Honolulu Fire Department captain. “It would really expand the potential for fire to spread.”

Investigators still have not determined what caused the Marco Polo fire, which killed three people and damaged more than 200 apartments in the 568-unit building. But residents have said they were surprised at how quickly the fire advanced from unit to unit.

Tom Schmidt, who has lived in the building since it opened in 1971 and used to sell units there as a Realtor, estimated that 30 percent of the Marco Polo apartments have secondary doors.

Sam Shenkus, who lives on the 31st floor, five above where the fire started, said four or five units on her floor have the louvered doors. Each floor has about 18 apartments.

Over the years, many Marco Polo owners have installed the louvered doors adjacent to the exterior side of the main ones, enabling the owners to boost air circulation while they are home but keep the apartments secured. The extra doors mostly are installed on the makai side of the S-shaped building, residents say, because those units tend to be hotter and typically do not get cooled by the tradewinds that directly hit the mauka units.

The mere installation of a secondary door does not violate Hawaii’s fire code, according to HFD spokesman Capt. David Jenkins. But propping open a fire door — designed to be kept closed as a fire barrier — would be a violation, he added.

The code states that a door normally required to be kept closed “shall not be secured in the open position at any time and shall be self-closing or automatic closing.”

The Fire Department does not go door to door in condo buildings to enforce the code and cannot enter private property to check whether a door is propped open, Jenkins said. “It’s up to building management for people to adhere to the fire code,” he added.

A spokesman for Associa Hawaii, which manages the Marco Polo, declined comment on the use of secondary doors, citing the ongoing investigation of the fire.

Shenkus, who served on the Marco Polo board for more than a decade and was president when she was voted off in 2013, said that while she was on the panel, the condo association did not get any indication from fire inspectors, who regularly came for inspections, that using the secondary doors violated regulations. The doors could be easily seen as inspectors walked through the hallways, she added.

“If it were against code, we would have done something about it,” Shenkus said.

She said owners did not have to seek permission from the condo association to install the louvered doors. If they saw a neighbor with the extra door and decided to install one, they just did it, she said.

Curtis Lum, a spokesman for the city Department of Planning and Permitting, which enforces the building code, said louvered doors in enclosed hallways in residential high-rises would not be permitted under the current code.

But he was unable Tuesday to say whether that was the case when the Marco Polo opened in 1971, adding that those records are in paper form and would require extensive research to determine the requirements back then.

Soo, who retired in 2002, said he couldn’t recall seeing any louvered doors in condo hallways when he did fire inspections. What he did see, he said, were security doors, but those and the main doors would always be closed, and he figured they were installed solely to enhance security.

Given what has happened at the Marco Polo, Soo said he thinks the city should crack down on the practice of using secondary doors to allow better ventilation.

“That is an unsafe practice,” he said.

Such a crackdown would affect more than the Marco Polo. Oahu condo owners in other old high-rises without sprinklers use louvered or screened doors to enhance air circulation in their units.

“You can go to any older building and you can see that happening everywhere,” said attorney Terry Revere, who represents condo residents and owns a unit in a high-rise without sprinklers.

As questions have been raised about the use of secondary doors at the Marco Polo, Jenkins urged people not to be diverted from the fire’s primary lesson.

“HFD does not want to lose sight of the main issue of absence of fire sprinklers,” he said. “We do not want to dilute the importance of fire sprinklers.”

The Fire Department has said that the Marco Polo blaze, which started in a 26th-floor unit, likely would have been confined to that apartment had the building had an automatic sprinkler system. The fatalities happened in neighboring units.

Marco Polo was built before sprinkler systems were required in residential high-rises on Oahu starting in 1975.

Jenkins said HFD will continue educating condo residents about the best ways to prevent and contain fires, including proper use of fire doors.