Can CO2 Levels in Cars Cause Drowsiness While Driving?

[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.