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Hydrogen Cyanide


Hydrogen cyanide is a colorless chemical compound. It is used in many industries in making products such as synthetic fibers, plastics, and pesticides. Oil refineries, including Suncor in Commerce City, emit it into the air as a byproduct. 

People who live near the refinery tell us they worry about hydrogen cyanide and whether it might harm their health. CDPHE understands these concerns.

CDPHE has monitored the air in neighborhoods around Suncor.  The department also has modeled hydrogen cyanide levels in the surrounding neighborhoods. Based on this modeling and monitoring, CDPHE does not believe hydrogen cyanide is a health risk for people in the area. The department  will keep gathering information about how much hydrogen cyanide is in the air around Suncor and will continue to evaluate this concern.


Hydrogen Cyanide and Your Health


Whether a substance will harm your health depends on how much you are exposed to and for how long.

So far, our data show hydrogen cyanide emissions from Suncor are well below health guideline values.

Breathing in high levels of hydrogen cyanide (above what CDPHE has seen around Suncor) for long periods can cause:

  • Breathing difficulties.
  • Chest pain.
  • Vomiting.
  • Blood changes.
  • Headaches.
  • Thyroid gland enlargement.

Breathing in very high hydrogen cyanide levels for short periods can harm the brain and heart and cause coma, and death.

More information from the Agency for Toxic Substances and Disease Registry.


Scientists set health-based guidelines for exposures much lower than levels at which we would expect to see health effects. When you spend less time exposed to a substance, the level needed to damage your health is greater. But, smaller amounts of a substance can build up over a long period and affect your health.

A level above a health-based guideline doesn’t mean bad things will happen to your health. Instead, it means there might be an effect on your health and that more investigation may be needed.

The difference between short-term and long-term exposure is important. You could be exposed for a few minutes to a level of hydrogen cyanide above a long-term health guideline and not have any health effects.

For hydrogen cyanide, CDPHE uses:

For short-term exposures, 303 parts per billion: EPA does not have a short-term health guideline value for hydrogen cyanide. The department uses California's guideline. It is set to protect against severe health effects, such as loss of coordination and consciousness, over a one-hour exposure.

For long-term exposures, 0.7 parts per billion: This guideline is from the U.S. EPA. It estimates the level at which people can be exposed continuously over a lifetime that is not likely to harm their health.

CDPHE required Suncor to hire an outside monitoring company to evaluate hydrogen cyanide emission levels at plants 1 and 2. The monitoring company  has done 2,225 hours of testing at Plant 1 and 1,443 hours of testing at Plant 2. Suncor will do more testing in 2021. 

Based on this monitoring, the highest emission rate for Plant 1 was 3.21 pounds per hour. The rate at Plant 2 was 1.11 pounds per hour. 

CDPHE also conducted modeling to assess hydrogen cyanide exposures in the areas surrounding the refinery.  CDPHE based the latest modeling (June 2019) on higher hourly emission rates -- 4.54 pounds per hour at Plant 1 and 4.54 pounds per hour at Plant 2.

Finally, CDPHE has conducted two rounds of direct measurements of hydrogen cyanide levels in the neighborhoods around Suncor. The department will continue additional direct measurement in 2021.

Modeling is a way of estimating concentrations of a pollutant at places downwind of a facility. We put important information into a computer program. This information includes hourly emission rates from the facility (pounds per hour), weather data for at least one year (wind speed and wind direction), and other facility information. The program then develops estimated (“modeled”) concentrations of pollutants for different areas around the facility. CDPHE compares the estimated concentrations to health-based guidelines to see if there are potential concerns for individuals or communities.

CDPHE has conducted many rounds of modeling at different emission rates. All have shown short- and long-term exposures below the health-based guideline values.

The latest modeling (2019) used total emission rates for Plants 1 and 2 that were more than twice as high as previously used.  This modeling showed maximum short- and long-term exposure levels were well below  health guideline values:

Short-term (one-hour) results:  The highest concentration was 2.35 parts per billion. That is 100 times below the California health-based guideline of 303 parts per billion.

Long-term (annual): results: The highest annual concentration was 0.140 parts per billion. That is five times below the EPA's health-based guideline of 0.7 parts per billion.

Also, CDPHE's two rounds of recent neighborhood monitoring did not detect hydrogen cyanide concentrations at any site.




The current data show people living near Suncor are not at risk from the refinery's hydrogen cyanide emissions. CDPHE will continue to get more data about emissions from the facility and levels in the nearby neighborhoods. CDPHE is committed to using the most recent information to answer this question.

Hydrogen Cyanide and Regulations


The Suncor refinery is regulated under Title V of the Clean Air Act, a federal law. Title V requires big facilities like Suncor to get an operating permit that governs and regulates operations, including what is emitted (released into the air).

But while the Clean Air Act is a federal law, states play an essential role. States develop programs to put Title V in place and review permit applications. State programs must comply with the federal Clean Air Act.

Yes. The process of refining fuel creates hydrogen cyanide. But Suncor’s emissions are not at a level that exceeds health guidelines.


No law prevents refineries from emitting hydrogen cyanide. The U.S. Environmental Protection Agency (EPA) has not set a limit for hydrogen cyanide emissions. To control hydrogen cyanide, EPA says refineries can run their equipment to meet emission limits for carbon monoxide, another byproduct of oil refining.

The Suncor Title V permit for Plant 1 has an annual emission limit for hydrogen cyanide. Suncor must conduct more air monitoring to find out if that limit is appropriate. The results of the monitoring might establish a limit for Plant 2.

Permit applicants can ask for emissions limits for some substances. CDPHE reviews these requests to figure out if they meet requirements. CDPHE must issue the permit if the requested limit does not violate federal or state laws and regulations.

This process is how CDPHE set the current hydrogen cyanide limit for Suncor Plant 1. As a part of its work on the permit, CDPHE  conducted air quality modeling. CDPHE concluded emissions at the requested level would not pose a health risk to people around Suncor.

Yes. The settlement the state announced in March 2020 resolved violations. One was an incident in which Suncor violated its emissions limit for hydrogen cyanide.