Can CO2 Levels in Cars Cause Drowsiness While Driving?

[russ_watters]

So, this question piqued my interest enough that I'm going to geek-out on it a bit. For those of you who don't know, I'm an HVAC/energy engineer and my specialty, if I can be said to have one, is lab ventilation. So I'm constantly thinking about issues like this one. Further, I'm always looking for an excuse to buy a new tax-deductable tool for my work, so I bought a carbon dioxide logger (also logs temp and humidity) to test the issue.

Background/Standards:
OSHA TWA-PEL: .5%/5,000 ppm (8-hour Time-Weighted Average Personnel Exposure Limit)
Noticeable breathing elevation/headaches: 2%
Normal Spacecraft: 0.5%
Apollo 13: "Approaching 2%"

5,000 ppm is the relevant limit, but I include the other information for reference.

Setup:
I will be driving my normal routes to and from work (as well as others), with the CO₂/Temp/Humidity logger in the passenger seat, at 15 second intervals. My car is a Kia Optima SX (interior volume: 3.33 cubic meters/118 cubic feet), which has automatic climate control. I keep it in semi-manual mode, with only the temperature controlled automatically. I'll do a humidity purge (open all the windows for a few seconds) at the start of each test. Air will be supplied to the front and floor vents: the climate control will not allow the windshield vents open without the outside air damper being open. I'll conduct full-length trials with the OA damper open and closed and note any potential upset conditions when they occur (such as getting stuck behind a school bus). Drive times vary from 30-60 minutes and I have two different routes, to work is all "city" driving, home is a mixture of open and congested highway. I'll be alone in the car for all trials.

Hypotheses:
1. My primary hypothesis is that at no time will a closed OA damper result in CO₂ levels exceeding the OSHA PEL of 5,000 ppm. My prediction is a steady state of 300-500 ppm above ambient (reached within the time limit of the test), but it may be higher in slow speed driving and/or lower in high speed driving.

2. My secondary hypothesis is that being behind a bus or truck with a low exhaust and the OA damper open will have a substantial impact on concentrations, approaching and perhaps even exceeding the OSHA PEL for short periods of time. Even now, when I have the OA damper open and get behind a bus, I close it. For the test, I'll resist that urge.

Limitations:
Humidity will be a significant limitation and this test would be better in the summer, when air conditioning removes it. I checked, and my car will not allow the air conditioning to run in the winter, even in manual mode. So I may have to abort some of the tests. Adding more people would add more CO₂, but in winter, having 4 people in a car will cause condensation in seconds, so it isn't possible. If the steady-state CO₂ level is too low with just me in the car or if I can't keep the OA damper closed long enough for SS to be approached, the test may have to be repeated in the summer.

 

[russ_watters]

Here's trial 1, with the OA damper open:

Weather was about 35F with a 25F dewpoint, which matches the humidity in the car pretty closely. For trial 1a, I suspect I breathed on the logger when turning it on -- I'll try to avoid that in the future. It's also possible that's from backing-through my exhaust plume on the way out of the driveway. Anyway, the concentration seemed to follow the traffic on my way to work. I didn't get behind a bus though, so I'll try that a few more times until I do. Again, the trip to work is in "city" traffic and the trip home is on a highway. Concentrations follow speed and traffic, as expected.

Tomorrow will be a bit different from the plan, as I am traveling a long distance to a client's location. I'll try to leave the damper closed as long as possible. It will be snowing though, so that will make the fogging on the windshield worse.

 

[zoobyshoe]

I was going to bring up the VW as one of the very very few cars that had been made too air tight. almost all other makes of cars have a near built in level of leakage including through the back seat into the trunk which allows the doors to close without arm breaking strength to do it and not popping the passengers eardrums.

Late in the game VW fitted the Beetle with vents behind the rear side windows that allowed air out. The point wasn't to avoid popping eardrums, interestingly, but to finally address complaints about the Beetle's heating system. The cabin was always so airtight it wouldn't allow more air, hot or cold, in.

11) The "crescents" located behind the rear quarter windiows are also part of the heater system. It is well known and documented that Beetles are sealed well and pretty air-tight. The crescents aid in cabin pressure relief. Without a means of relieving cabin pressure, the cooling fan no longer has the ability to move air once the cabin becomes pressurized. Air travels from areas of high pressure to areas of low pressure, so once cabin pressure equals the output of the fan, air flow ceases. Before the addition of the crescents, VW recommended cracking a window open to allow the heater to function more efficiently. The drawback to this was that the hot air would escape the cabin before having a chance to warm most of the interior. By positioning the crescents at the rear of the vehicle, warm air entering the cabin in a direction toward the front of the vehicle would circle the front of the vehicle, then head toward the rear due to the location of the pressure relief. This allowed for more consistent and thorough heating of the interior.

http://www.thesamba.com/vw/forum/viewtopic.php?t=434051

So, all cars must have a modicum of ventilation for the heating system to work, if they take outside air, heat it, and introduce it into the cabin. The alternative would be for air that is already in the cabin to be removed from the cabin, put through a heater, then returned to the cabin. The former would prevent undue CO2 buildup but the latter wouldn't.

 

[dragoneyes001]

the fun thing with the really old VW's was they could float for quite an extended period. this is still used in places to cross wide rivers where the bug is allowed to float out and work its way across by judiciously not flooding the engine (some off roaders use snorkels).

I'm really interested in the results from russ's tests. since the first run looks to be an average around 800ppm i'd estimate an all closed run shouldn't surpass 2kppm

 

[russ_watters]

I'm calling this trial 3 due to the different driving profile:

Outside air was 20F, Dewpoint 14F.
For this trial, I was driving a long distance to a client's site during the second worst of the three snowstorms this past four days (oddly, "The Storm of the Century" was third-worst, even though none was worth writing home about...). Sorry it isn't scaled the same as the previous, but the profile is enough different it would have been tough to scale similarly without missing some information.

As you can probably tell, I drove for a while with the OA damper closed, then opened it to purge when the windows fogged-up enough to bother me. I drove far enough that it did get a bit cooler as I drove, but much of the variation in concentrations (of both CO₂ and moisture) is definitely due to driving speeds: The first 20 minutes or so was very slow due to local snow, and then I got on a highway, which wasn't too bad (probably averaged 50 mph). As discussed previously, since the human body exhales much more water vapor than CO₂, the water vapor reached steady state quickly. The steady state is lower at higher speed due to the wind speed making the windows colder. As condensation increases, it also slows, so that explains why the steady state is not quite steady.

The CO₂, did not reach steady, state, as I feared. And the peaks don't look anywhere close to steady state, either. As it is, the high was above my prediction, though not yet anywhere close to the OSHA limit (which was also part of the prediction). One can speculate that in heavy/slow traffic on a calm day, it is conceivable that the OSHA limit could be reached.

It is going to be very dry tomorrow, so I may be able to go longer than the 15-20 minutes in the above test. But I think I'll probably need to repeat this in the spring.

 

[russ_watters]

Trial 2:

2a ambient: 20F, 0F DPT
2b ambient: 30F, 5F DPT

These trials nearly but not quite reach steady-state, with 2a being at low speed "city" driving and trial 2b being higher speed highway. I was able to keep the OA damper closed the entire time for both. The morning trip required wiping the condensation off the windshield.

An additional test of interest:

Ambient: 34 F, 30F DPT
This was a trip to visit a client, on a very windy day. I left work an hour and a half after ariving and the car's indoor CO₂ level had not yet returned to ambient, which is why it started near 1,200 ppm. The wind had a major effect on the CO₂ levels.

Conclusions:
The highest level recorded was just under 2,800 ppm and varied widely based on weather and driving conditions. This was higher than predicted, but still well below the OSHA 8-hour time-weighted average personnel exposure limit of 4,000 ppm. With more people in the car the potential exists to exceed the OSHA limit, particularly in the summer when humidity can be controlled by the air conditioning. A long highway drive with 2 people in the car is unlikely to exceed the OSHA limit, but 3 or more people may. And if you take a long trip with 2+ hours between stops and 2 or more people in the car in heavy traffic (say, you drive the northeast corridor on the Wednesday before Thanksgiving), the limit likely will be exceeded. So it may be a good idea to open the outside air damper periodically or leave it open (depending on weather) when driving long distances with multiple people in the car. However...more on an alternative risk later...

 

[dragoneyes001]

I'm surprised the levels were that high. I'd expect more leakage even with the damper closed guess cars are being made with higher specs than I believed they were.

 

[russ_watters]

Some additional research:

A good (and short!) article on the physiological effects of CO2 exposure and government exposure limits:
http://www.blm.gov/style/medialib/blm/wy/information/NEPA/cfodocs/howell.Par.2800.File.dat/25apxC.pdf

Here's an article covering the entire issue, and gets to the "alternative risk" I alluded to earlier:
http://www.futurity.org/clear-highway-smog-recirculate-car-ventilation/
Unfortunately, the full paper is behind a paywall: http://pubs.acs.org/doi/pdf/10.1021/es401500c

Setting a car’s ventilation system to “recirculate” is the best way to reduce exposure to harmful traffic pollution.

That’s the advice researchers have for parents as millions of children return to school, many of them driven in cars on the highway.

Environmental health researchers recently conducted the first systematic measurements of in-vehicle exposure that included a full range of car types and operating conditions, and for all types of particulate pollution.

“Short of driving less, putting your ventilation to ‘recirculate’ is the best way to reduce exposure to all types of vehicle-related particulate

That part was my main concern, but I have not been able to replicate their finding yet. Reading further, they say that the exposure is worse on freeways than local roads, but the study appears to have been conducted in LA, which is uniquely dense in the world for that sort of thing. They have 12-lane highways, with people bumper-to-bumper all the time, whereas my drive home is on a 4-lane highway. So my conditions do not correspond. I may be able to partially replicate it if I ever get behind a bus again...

I only measured CO₂, not other pollutants, so I don't know what else they looked at/found. It's too bad I don't still work for my previous company, as they had a combustion gas analyzer and other pollutants are much more harmful even in trace amounts -- if you can smell it (and if it is making your windows greasy), it is probably at a harmful concentration.

But this pretty much exactly matches my findings and the main point of the thread:

The researchers also found that leaving the windows closed over 30-minute or longer drives with several passengers raised carbon dioxide levels in tight new cars to those of stuffy meeting rooms.

“Some people are sensitive to high CO₂ concentrations. To prevent this, outside air should be pulled in every 10 or 15 minutes for a minute or two, especially if there are two or more people in the vehicle,” Hudda says.

Though I'm interested in the actual study, I think I've spent enough money on this and the quotes in the article pretty much exactly match my findings, so someone else (Ivan?) can buy the full study if they want.

Another related study:
http://www.engr.ucr.edu/~heejung/publications/2013-CO2-model.pdf

They have some good graphs that look simiar to mine, but show higher concentrations. Unfortunately, they only tested at one, slow speed (21 km/h), but varied fan speed and number of people in the car. It would have been nice if they had tested at multiple speeds. Clearly from my results speed matters, but while I think it would be linear/inverse (er; hyperbolic), my speeds are too erratic to show that.

 

[256bits]

Here is a discussion on Airline Cabin Environment.
http://www.donaldson.com/en/aircraft/cabinairquality/supportDocs/18%20Issues%20Pertaining%20to%20Flight%20Attendant%20Comfort.pdf

Figure 7 . Page 5 shows several adopted standards and CO2 levels.
OHSA at 5000 ppm, 1881 ASHRAE at 2500 ppm ( which resulted in sick building syndrome due to the lessor air exchange ), 1989 ASHRAE at 1000 ppm ( better air quality ) , airline cabin at 600 to 1500 ppm. Noteworthy, is that in the lungs themselves the CO2 level is 50,000 ppm.

Figure 6. shows respiratory effects of CO2 concentration.

Airline cabins CO2 levels, apparently due to the frequent air exchange, do not reach that as witnessed by Russ in his own experience within a car interior.