Carbon Dioxide: Silent but Deadly

“You will die but the carbon will not; its career does not end with you.”  — Jacob Bronowski

A few months ago, I wrote about a project that Bluefield was undertaking to understand the carbon dioxide levels in and around alcohol fermenters. Particularly the fermenters in craft distilleries and microbreweries. I promised to keep everyone posted on our progress.

Recently, Nathan Breshears from Bluefield Process Safety attended the AIChE Global Congress on Process Safety in Houston to present our work during the poster session.

This is the gist of what his paper, “Craft Distilleries: Exposure to Toxic Concentrations of Carbon Dioxide,” had to say:

The Hazard: Carbon Dioxide Exposure

The Occupational Safety and Health Administration (OSHA) has established a Permissible Exposure Limit (PEL) for CO₂ of 5,000 ppm (0.5%). That means that workers should not be exposed to environments that contain more than 12.5 times the CO₂ normally found in the atmosphere.

The National Institute of Occupational Safety and Health (NIOSH) has established the level of CO₂ that is Immediately Dangerous to Life and Health (IDLH) as 40,000 ppm (4%). This is based on acute toxicity and means that people should not be exposed to atmospheres containing more CO₂ that is in the breath we exhale.

Carbon Dioxide in the Beverage Alcohol Industry

When breweries or distilleries produce beverage alcohol by the fermentation of sugars, yeast consumes sugars and converts them to ethanol and CO₂. For every molecule of ethanol produced, fermentation also produces a molecule of CO₂ During fermentation, the yeast produces 27.46 standard cubic feet of CO₂ for every proof gallon of ethanol produced.

[A proof gallon is the amount of ethanol contained in one gallon of 100 proof alcohol, also known as 50% ABV – alcohol by volume.]

Breweries keep their fermenters enclosed in order to exclude foreign microorganisms from falling into the fermenting beer and ruining its flavor. Most distillers, however, tend to not worry about foreign microorganisms, knowing that they will distill the wash, or distiller’s beer, and that the flavor profile develops primarily as purified ethanol ages in charred oak barrels.

Both breweries and distilleries, however, typically release the CO₂ by-product directly into the room housing the fermenters.

A Problem, but Manageable

Nathan found that CO₂ levels varied in and around fermentation facilities.

Outdoor levels were consistently around 400 ppm, regardless of the facility, as was expected.

Indoor levels were always higher than outdoor levels, in the range of 500 ppm to 650 ppm. Indoor levels depended on the amount of human activity in the building.

On the other hand, the CO₂ levels in the headspace of the fermenters, immediately above the liquid, always pegged the meter, which could only read up to 10,000 ppm (1%). This means that CO₂ levels in the headspace of the fermenters always exceeded the OSHA PEL for CO₂ and probably exceeded the NIOSH IDLH.

Nathan also looked at two intermediate spaces: near the discharge of the fermenter vent, and in the fermenter room. He found that the CO2 levels in the two spaces were linked, and changed as fermentation progressed.

Early in the fermentation, levels in the fermenter room were 10 to 50 ppm higher than background indoor levels, meaning that human activity contributed more than fermentation to elevated CO₂ levels, but that fermentation was contributing. Near the discharge of the fermenter vents, CO₂ levels were typically much higher early in the fermentation—800 to 1000 ppm higher than the background indoor levels.

At the peak fermentation rate, CO₂ levels also peaked. Near the discharge of the fermenter vent, the CO₂ levels were usually above 2000 ppm, and in some instances, above the OSHA PEL. In the fermenter rooms that Nathan examined, the CO₂ levels were elevated, but never more than 200 ppm above the background indoor CO₂ levels, well below the OSHA PEL.

Permit-Required Confined Space Entries

When it comes to CO₂, the most hazardous space in a brewery or distillery is the headspace of the fermenter. The gas immediately above the fermenting liquid quickly fill with CO₂, which displaces the air in the headspace. The displacement begins immediately upon the introduction of yeast, even before bubbling is discernable. As a result, the headspace is a hazardous space.

Most breweries and distilleries recognize that fermenters meet the definition of permit-required confined spaces, but fail to recognize that reaching into the fermenter is a permit-required confined space entry. It is important to realize that when any part of the body breaks the plane of confined space opening, OSHA considers that a confined space entry.

CO₂ Levels in Fermenter Rooms

While not confined spaces, fermenter rooms may have areas that exceed the OSHA PEL for CO₂, especially near the discharge of the fermenter vent. When fermenters are enclosed and vented outdoors, the CO₂ level is unlikely to be too high, except right at the discharge. A good engineering practice is to have the vent pipe discharge at an elevation of 10 feet (3 meters) above the working surface. This will allow natural outdoor convection to disperse the CO₂.

When the fermenters are indoors and release directly into the fermenter room, then good ventilation will make an important difference. The National Fire Protection Association considers six air changes per hour to be adequate ventilation when addressing flammable vapors. Hazardous levels of CO₂ are similar to the hazardous levels of many flammable vapors.

Staying Safe

In a room without adequate ventilation, CO₂ will accumulate, perhaps to dangerous levels. In a room with adequate ventilation, CO₂ will likely be diluted with fresh air and kept at safe levels.

Monitoring CO₂ levels is simple and inexpensive. Because the levels of CO₂ that are problematic are not enough to reduce oxygen to a dangerously low level, it is important to use CO₂ meters rather than oxygen meters. However, with routine CO₂ monitoring, brewery and distillery operators can maintain a working environment free from excess CO₂.