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Does Enough Air Come Through A Car's Vents To Keep The Occupants From Suffocating?


LisaL

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would the amount of air getting through the vents differ much by car? I wonder if there's been any studies which show how much air gets through the vents and if it's enough to keep occupants with enough air for 13+ hours

I read modern cars these days are air tight and I did recall reading about kids who got trapped in cars and ended up suffocating 

there was an article on that 2 days ago. 

Edited by LisaL
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It may be just anecdotal but I have spent several nights in a car with the windows rolled up with four people, we are still here...

My experience is the same.

 

I was a car-dwelling homeless person for 2 years, including winters I sleep, sometime with one other person, in a small car with not only its windows up, but its dash/hood vents covered in snow.

 

Searching the internet, I find a telling absence of credible stories of people suffocating in cars, so I’m pretty sure people suffocating cars with motors off has happen only very rarely, if at all.

 

would the amount of air getting through the vents differ much by car? I wonder if there's been any studies which show how much air gets through the vents and if it's enough to keep occupants with enough air for 13+ hours

The amount of air and oxygen in the car, and the amount needed by a human, are important factors.

 

A small car contains about 4 m2 of air, of which about 0.8 m2 is O2, and a person needs about 0.5 m2 of O2 a day. Once the O2 in the car decreases to about 0.2 L, the average person couldn’t breathe fast enough to survive, so in a completely sealed small car, 1 person would survive about 24 hours.

 

I read modern cars these days are air tight and I did recall reading about kids who got trapped in cars and ended up suffocating

Pets, infants, or older children for some reason unable to escape them, die in parked cars with awful regularity (According to this parenting advice webpage, 38 (per year? In the US?)). Though usually called death by suffocation – the inability to breath – the deaths are actually due to being too hot, due to the greenhouse effect of sunlight through the car windows. This oft-quoted description (one source is http://www.answers.com/Q/Can_you_die_of_suffocation_sleeping_in_car, though I’ve not been able to find a primary one) is, I think, accurate

If a car is parked in the sun with outside temperature of 90oF (32oC), the temperature inside the car could rise up to 140oF (60oC) because of the trapped heat. Normal body temperature is 98.6oF... At 107oF (42oC) we begin to lose consciousness and the body stops to function. Under these circumstances, the small openings discussed above are insufficient to prevent heat build up

I read a Daily Mail article that said a couple almost suffocated after they were locked in a car overnight.

Lisa, please post a link to the story, so readers can investigate it.

 

My guess, based on similar stories I read while researching this post, is that the people didn’t “almost suffocate”, but experience panic/anxiety that they would, based on myths and rumors they’d heard, and a poor understanding of science.

Edited by CraigD
Fixed incorrect unit (m^2 for L)
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This is referring to people in the cabin of the car, not the trunk. How long it would take two people in a small car to use up enough oxygen for it to be dangerous (below 17%) assuming the car is air tight, and roughly how much air comes through the vents if the car isn't moving and the windows can't be opened.

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This is referring to people in the cabin of the car, not the trunk. How long it would take two people in a small car to use up enough oxygen for it to be dangerous (below 17%) assuming the car is air tight, and roughly how much air comes through the vents if the car isn't moving and the windows can't be opened.

Cars are not air tight, why would you set up such a model?

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I guess one wouldn't last long in the trunk??

In most of the front engine cars with a true trunk (ie: not a hatchback) I’ve looked closely enough to see the details of its trunk, all that separates the trunk from the main cabin is the rear seat back or some a thin material, attached in a not very airtight way. Also, since the tail lights pass through the body in the trunk area, and trunk lids usually aren’t gasketed very tightly, there’s usually a lot of airflow into and out of the trunk. So I doubt you’d suffocate inside most car trunks, provided it wasn’t very hot outside, or the car in strong sunlight.

 

As with pets and babies left in cars, high temperature inside a trunk can be fatal, even if there’s enough ventilation for O2 to get in and CO2 out. One such case was the June 2005 deaths of an 11, 6, and 5 year old child when they accidentally locked themselves in a parked car trunk (source: http://www.nytimes.com/2005/06/25/nyregion/3-camden-boys-found-dead-in-trunk-of-car-in-yard.html)

 

Cars may not be air tight, but that does not mean that enough air passively diffuses through vents fast enough to prevent 2 people in a compact from running the risk of using up more oxygen than comes through the vent.

It would be complicated, I think, to calculate an answer to this question, because of how complicated the diffuse of O2 and CO2 and other gasses in air and the human body is to calculate. It’s a function of the difference in partial pressures of the various gasses in the various volumes of air, areas of contact between the volumes, and airflow, which depends on many factors. I’m daunted by the prospect of such a calculation!

 

An experimental approach would be easier, I think – just get a oximeter (finger clip-on ones can be bought in pharmacies for under US$100 – eg: here), one or three friends, a car, and sit around in it while monitoring your blood’s saO2. When it drops from the normal of 90%+ toward 50%, you’re beginning to get anoxia, and better stop the experiment before you all die. :)

 

Another approach is to survey news and mortality databases for mentions of death due to anoxia from suffocation in a car. I’ve not found any, and have found mentions on other forum sites of not having found any, so, as I concluded in my first reply in this thread, I’m pretty sure people suffocating in cool cars with motors off has happen only very rarely, if at all.

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I found an article which says ACH (Air Changes Per Hour) in a stationary vehicle w/o mechanical ventilation (and windows up) ranges from 1-3 Air Changes Per Hour.

 

However that study was only done on 3 vehicles, in 1998. Are more modern cars more 'air tight' per se? (Smaller vents, tighter seals?)

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