DENVER -- The mixture of common swimming pool chemicals outside a hospital pool created noxious fumes that prompted National Jewish Hospital to evacuate about 500 people Monday morning.

The "all clear" was given at about 12:25 p.m., and the evacuation order was lifted.

Before that, at least 44 people were transported by ambulance to other hospitals, including two people who were rushed to emergency rooms. Most needed treatment for nausea and respiratory irritation, a National Jewish Hospital spokesman said.

"It was nothing serious. A mild respiratory irritant," said Adam Dormuth, a spokesman with National Jewish Hospital. "With the exception of the 44 people that had to be transported to local hospitals, I think the impact, really, was very minimal."

Dormuth said that routine pool maintenance was being conducted at about 8 a.m. when hydrochloric acid spilled and came into contact with sodium hypochlorite or bleach. The two chemicals are normally mixed in the water, but someone mixed it outside the pool, causing irritating fumes to spread through the ventilation system to the connected buildings, Dormuth said.

Inhalation of the mixture can cause persistent asthma or lung irritation. That is especially troublesome for patients at National Jewish, which specializes in treating respiratory problems.

"I've never seen anything like this before here," said National Jewish employee David Gurka. "I work in the pulmonary physiology unit where we actually test the patients. We test their lung functions. So that's not a really great thing to do when there's a chemical irritant in the air."

"We do specialize as a respiratory hospital, so while you never like to see this happen, the folks here were certainly qualified to address the situation," said Dormuth.

Six buildings in the hospital complex were evacuated, including the Kunsberg School -- a K-8 school for children with severe asthma and chronic respiratory illnesses. Two of the 60 students at the school had to be transported for treatment, Dormuth said.

The noxious chemical vapors also traveled through the underground tunnels that connect all the buildings of National Jewish.

"We were a little surprised by the rapid spread throughout all the structures. This is a campus setting, but because of the underground labyrinth of tunnels, it was able to spread rather quickly," said Denver Fire spokesman Phil Champagne.

The tunnels run across Colorado Boulevard and hospital staffers believe they date back to World War II era.

All of the students were released for the day, but normal school hours will resume Tuesday. Parents of the Kunsberg students had to pick up their children at Denver Fire Station No. 14 at 14th Avenue and Harrison Street.

Of the nine buildings on the hospital campus, only three were not evacuated, including the main hospital building that houses the majority of patients. Many school workers and hospital staff members had to evacuate, but not many patients.

Firefighters said they arrived quickly after the call of the spill but the mixture had already begun to release gas fumes.

"We were in a dilemma because it had begun to off-gas. It was in the process. We couldn't cap the content or the product, obviously. We certainly didn't want an explosion," Champagne said.

Firefighters diluted the chemicals and continued to test the air until it was clear.

"We were able to flush the product down the drain, in essence," Champagne said. "Any long term health effects probably are nil."

The campus was reopened by 12:30 p.m. Patients who had an appointment Monday afternoon were still able keep it.

Fourteenth Avenue was closed from Harrison Street to Colorado Boulevard, and 13th Avenue was closed from Colorado Boulevard to Harrison Street.

The pool is used for physical therapy.

Additional Resources:

National Jewish
Kunsberg School