by – Mark Frame, PE, Mechanical Engineer
Don’t Let High Energy Cost Take Your Breath Away!!
Have you fallen asleep in meetings even after a good night’s rest, or felt like you were not able to concentrate? Do you sometimes wake up with a slight hangover, even when you didn’t have any alcohol the night before? Do you sometimes feel hot in crowded rooms, even if the temperature is not high? Do you often feel terrible after a long flight? You may be feeling the effects of excess carbon dioxide (CO2).
Most of us were warned as children never to put a plastic bag over our heads. Before a law changed the way refrigerators latch, many children died trapped inside abandoned refrigerators. I always thought that it was a lack of oxygen (O2) that caused death in such cases. But it turns out that people trapped in an airtight space die long before the space runs out of O2. The cause of death is lack of O2 getting to the brain, but that happens because their blood cannot get rid of CO2 so that it can absorb O2.
By volume, dry air contains approximately 78% nitrogen, 21% O2, 0.93% argon, 0.04% CO2, and small amounts of other gases. When we breathe, O2 from the air is exposed to blood returning to our lungs after interacting with cells throughout the body. All those cells had taken in O2 and given off CO2 in return, so the blood is O2 depleted and CO2 rich. What drives the O2/CO2 exchange in our lungs is that each gas tries to move to a place where there is less pressure for that gas. The CO2 in the blood recognizes the air in the lungs as a place of lesser pressure and detaches from our red blood cells to move into the air. Meanwhile, since there is so little O2 in the blood, some of the O2 in the air attaches itself to the same red blood cells that just released CO2.
Outside air is about 400 parts per million (ppm) of CO2. The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) recommends a CO2 upper limit of 1000 ppm. Most people begin to notice changes like feeling tired, not concentrating well, or feeling warmer than the room really is when CO2 levels reach 2000 to 3000 ppm. A Berkeley study documented a significant reduction in decision-making ability when people were exposed to 2500 ppm. And most of us feel pretty lousy after a long flight, where the concentration can reach 5000 ppm before exceeding the limit FAA allows. None of these are symptoms are surprising once you realize that when the CO2 levels are higher, your brain does not get as much oxygen because it is harder for your body to get rid of the CO2.
The Occupational Safety & Health Administration (OSHA) limits CO2 to 5000 ppm (0.5% of air volume, or 12.5 times the CO2 level in outside air) for an 8-hour work shift. People may not feel their best at that level, but there are many legal working conditions that are less than ideal. Your office is fine, unless you fill it with six people and close the door for hours. That crowded conference room? Well, the meeting only lasts for an hour and if the ventilation was designed correctly it should still be fine. Your house—how many people live there? How big is it? How tight is it? Is there a ventilation system, and has that been maintained lately and do you run it?
Modern vapor barriers seal so tightly that people inside are, in a very real sense, in a large plastic bag! With windows and doors closed and ventilation off, it is difficult for O2 to get in and for CO2 to get out. Breathing people can quickly raise CO2 above recommended limits. A bedroom that is not ventilated, where the door stays shut all night and the windows are not cracked open, could be a problem. If you or someone you know has a concern, CO2 meters cost around $150. If you find a problem or have a question, ask one of your friendly mechanical engineers for suggestions. I personally have helped many friends and coworkers figure out if their house was getting enough fresh air, and what to do if it wasn’t.
A related recommendation—GET OUT-OF-DOORS MORE OFTEN!!!!!