Malfunctions after a power outage at the Suncor Energy oil refinery just north of Denver triggered toxic belches spewing more than 100 pounds of hydrogen sulfide and more than 500 pounds of sulfur dioxide gas into the air, exceeding state air quality limits.

The refinery also emitted carbon monoxide at concentrations up to 1,120 parts per million, according to a company report submitted to state health officials and reviewed by The Denver Post.

This was the second time in five months that a power-supply hiccup led to a sudden burst of toxic air pollution from the refinery. It’s the latest challenge at one of Colorado’s most problematic industrial sites.

Xcel Energy officials said power was out for 6 minutes Saturday night. Suncor spokeswoman Lisha Burnett on Thursday said power was out for more than 13 hours starting at 9:54 p.m. The unexpected power interruption triggered automatic and manual safety shut downs and refinery still wasn’t back to normal operations, Burnett said.

“Xcel Energy’s failure to provide the refinery with a continuous power feed caused a temporary inability of Suncor to comply with certain of its permit limits,” she said. “The loss of power was completely outside of Suncor’s control, and Suncor took a number of measures to minimize the impacts and reduce emissions caused by the loss of power.”

Suncor officials responded to the problem by closing Brighton Boulevard between 56th and 60th avenues Saturday night. Suncor also sent air-monitoring trucks into surrounding neighborhoods.

Company officials told local authorities no toxic chemicals had been detected in the surrounding neighborhoods.

Hydrogen sulfide, a toxic byproduct of refining and burning oil, can kill. The Environmental Protection Agency has not set a national air quality limit for hydrogen sulfide because any exposure is considered dangerous.

Sulfur dioxide also comes from burning fossil fuels and can inflame airways, especially in people with asthma. High concentrations of sulfur dioxide worsen particulate air pollution that can penetrate lungs. The EPA has set a health limit of 75 parts per billion for sulfur dioxide, but it’s unclear whether authorities are measuring comprehensively and enforcing that limit. Carbon monoxide can impair oxygen delivery to tissues, the heart and brain.

Colorado Department of Public Health and Environment officials this week said they have not completed a review of the Oct. 14 Suncor incident in which an Xcel power failure resulted in the release of an estimated 75,600 pounds of sulfur dioxide — 150 times greater than the CDPHE daily limit of 500 pounds that triggers an investigation. That power outage lasted for seconds. A refinery emissions stack spewed orange-colored hydrocarbon-coated dust and gas, prompting road closures, a school lockdown and a warning to residents to remain indoors.

“The events of the power outage in October 2016 at Suncor are complex in nature, and CDPHE’s investigation of the incident is ongoing and deliberative,” air pollution control division director Garry Kaufman said in a response to Denver Post queries that was e-mailed by an agency spokesman. “There is no set date for completing the investigation. CDPHE has not issued a notice of violation or other enforcement document, possible or actual, related to the incident to date.”

But the health department has set annual limits that Suncor must meet covering numerous significant pollutants including sulfur dioxide, particulates, nitrogen oxides and carbon monoxide, Kaufman wrote. And Suncor cannot emit more than 0.3 pounds of sulfur dioxide per barrel of oil processed, he said.

The company would have to assert “an affirmative defense” to avoid civil penalties by showing state air quality rules don’t apply in the circumstances.

State regulators are treating the two mishaps as separate incidents. Before these incidents, CDPHE officials already were dealing with numerous previous chemical emissions problems at the plant.

CDPHE officials seemed to say there’s no health risk based on what Suncor officials have disclosed. The state has not conducted independent air tests.

“Upon initial review of the available air quality data, the measured concentrations of air pollutants at monitoring sites around the Suncor refinery remained well-below the health-based air quality standards during the power outage at Suncor,” Kaufman wrote. “Suncor personnel have deployed mobile air quality monitoring units around the perimeter of the refinery, at major intersections, and at schools in the area. Suncor’s monitors measure concentrations of hydrogen sulfide and sulfur dioxide in the air and have detected no readings of harmful emissions, according to Suncor representatives.”

Burnett said a full report will be submitted to state health department once the refinery returns to normal operations.

Xcel Energy spokeswoman Michelle Aguayo said “the actual outage lasted 6 minutes.” Aguayo added that in making repairs Xcel later shut down the power again.

Aguayo called the two Suncor outages “unrelated.”

The Oct. 14 power outage was caused by “a switching issue due to an Regional Transportation District request to relocate a transmission pole,” Aguayo said in an e-mailed response. “Saturday’s outage was the result of a sleeve failure on a transmission line, causing the line to fall into a distribution line that serves Suncor.”

Since 2013, state regulators have opened five cases against Suncor for possible air-quality violations, CDPHE records show. State officials are weighing possible penalties for previously identified deficiencies that include excessive sulfur dioxide and other gas emissions. In June, CDPHE officials notified Suncor officials their company could face penalties of up to $15,000 a day. In 2015, state regulators ordered Suncor to fix other pollution problems detected in 2013 and 2014. Suncor at one point negotiated a deal to avoid admitting law violations in return for paying a $214,050 administrative penalty.

Back in 2012, state regulators fined Suncor $2.2 million for air quality violations related to benzene air pollution from the refinery.

The Suncor refinery sits on an 80-year-old industrial site. Suncor bought the refinery in 2003 from ConocoPhillps in a $150 million deal. Over the past 13 years, Suncor has spent $1.6 billion on the plant.

Suncor officials have said it will play a key role in processing Suncor’s huge Canadian oil sands resources for the U.S. energy market.

Workers at the Commerce City refinery produce up to 98,000 barrels a day of gasoline and diesel fuel, jet fuel sent to Denver International Airport, and asphalt. A fifth of the oil produced at the refinery comes from the Athabasca oil sands in Canada.