If you’ve ever been to a concert, a theater, an indoor stadium or even a trade show, you know what it’s like to be in a large room with hundreds or even thousands of other people. Heating, ventilation, and air conditioning (HVAC) engineers spend countless hours designing air-handling systems to make you safe and comfortable in these venues.
The rule of thumb is that an HVAC system is properly designed when you don’t notice the system at all.
The challenge for venue or facility managers is that they must balance guest comfort and safety with expenses. In a way, it is no different than your home. If you feel a bit chilly and turn up the heat, you expect to pay a higher heating bill.
When it comes to guest safety, think of carbon dioxide (CO2) as the “canary in the coal mine.” Before the introduction of personal gas sensors, miners would carry a caged bird down into the coal tunnels with them. If dangerous gases were present they would kill the canary before killing the miners.
While high levels of CO2 are not normally dangerous, like the canary, high levels of carbon dioxide can be an indicator of poor air quality.
ASHRAE Standards for Acceptable Air Quality
In the United States, the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) sets guidelines for acceptable levels of CO2 in buildings. According to the Summary of Selected Air Quality Guidelines in ASHRAE Standard 62.1-2016, "Ventilation for Acceptable Indoor Air Quality"
“CO2 at very high concentrations (e.g. greater than 5,000 parts-per-million) can pose a health risk…However, in most buildings, concentrations almost never rise to these levels. CO2 at the concentrations commonly found in buildings is not a direct health risk, but CO2 concentrations can be used as an indicator of occupant odors (odorous bioeffluents) and occupant acceptance of these odors. At the activity levels found in typical office buildings, steady-state CO2 concentrations of about 700 ppm above outdoor air levels indicate an outdoor air ventilation rate of about 7.5 L/s/person (15 cfm/person). Laboratory and field studies have shown that this rate of ventilation will dilute odors from human bioeffluents to levels that will satisfy a substantial majority (about 80%) of unadapted persons (visitors) in a space…”
CO2 concentrations in outdoor air is about 400ppm. Therefore, ASHRAE recommends indoor CO2 levels to be no more than 1,100ppm. The Occupational Safety and Health Association (OSHA) standards state that 5,000ppm of CO2 is the maximum level allowed for workers over an 8-hour average, and this limit is a requirement in most building codes.
CO2 in Venues: A Real-World Example
The McCormick Place in Chicago, Illinois is the largest convention center in North America. During a trade show, CO2Meter had an opportunity to place a tSense CO2 transmitter in the Main Hall for 5 days. The CO2 levels varied from 400ppm to 2,400ppm with the lowest levels on days 1 and 5 (setup and tear down with bay doors open) and the highest levels during the actual trade show.
While the CO2 levels were never dangerous, this shows that respiration alone can impact the CO2 levels in a large structure. CO2 is heavier than air and tends to accumulate at floor level.
CO2 Tips for Better Indoor Air Quality
HVAC systems should be regularly inspected and tested when the venue is in use. While modern systems can change dynamically depending on the occupancy levels, older systems are often set on timers that automatically add fresh air to the venue’s environment on a set schedule. Too much fresh air wastes energy when the venue is empty, while too little fresh air can result in occupant discomfort.
An easy and inexpensive way to verify HVAC system is to purchase a hand-held CO2 meter like the SAN-10 Personal 5% CO2 Safety Monitor. By simply carrying it around the venue during an event you can quickly see if the HVAC system is working properly.
CO2 Safety Tips for Stored CO2
If a venue offers beer or carbonated beverages, or if it uses CO2 as a refrigerant, a CO2 Safety Alarm should be installed. A leak in a supply line or fitting can not only quickly raise the CO2 levels, but in an enclosed room can be dangerous.
For example, the RAD-0102-6 is designed to protect customers and workers around stored carbon dioxide in soft drink dispensing areas. It also has audible and visual alarms 1.5% CO2 and 3% CO2 that can control a ventilation fan or send an alarm to the fire department or monitoring company.
Our latest model RAD-0102-6 has an additional alarm that sounds if the 5,000ppm OSHA TWA (time-weighted average) for CO2 levels are exceeded in an 8-hour workday. Many local municipalities now require CO2 safety alarms in any venue that uses bulk CO2.