How Hot Are the Cars, Really?

Every Summer we see all those warnings about the dangers of leaving dogs in hot cars. Some of them with neat charts and scientific results. Many with very authoritative references. I’ll discuss how accurate and meaningful these warnings really are.

The Warning

According to the American Veterinary Medicine Association (AVMA), if the temperature outside is 70F degrees, in just 20 minutes it is 99F degrees in the car. If it’s 90F degrees outside, in that same ten minutes it is 109F degrees inside the car. They say lowering the windows has a minimal effect when it’s that hot outside. And all of that comes with a pretty chart showing the resulting temperatures in your car.

Yes, it does have a legend showing this is estimated data. But this actually comes from the Department of Geosciences, San Francisco State University. This is all science, from scientists, so it must be right. I’ve seen other charts, from other sources, with similar advice and results, which seems to imply that most scientists agree on this. But, are all scientists the same?

The Enforcement

Looking around for related news, I see people being yelled at for leaving their dogs in the car while pumping gas. Even though their air conditioner had previously been on, they were told science says the car will heat up like an oven. Elsewhere, police were called for obviously very hot dogs in a car sitting in the shade, on a cool day when people were wearing jackets.

A friend told me he was stopped outside a store with his dog in the car, and ran in to pick up something. The car was sitting in the shade and it was 91F outside. An animal control officer then warned him that he could get a citation for leaving the dog in a dangerously hot car, after she pulled out a thermometer and measured his car interior at the same 91F. He replied that he was currently sitting in that same car and was not hot, but she ignored him. Apparently, it was safe to walk your dog outside in the same temperature, but not sit in the car.

A woman transports her dog to many shows. Her car has a temperature monitor and cell phone alert, together with a cooling system and water for the dogs. She returned to her car just before police and some irate citizens were about to break her window. They never bothered to read the note she left there.

The Known Failures

Many of the deaths reported in the news are police K9 dogs as in this summary from just 2012 to 2014. I then selected similar ones that had published how long the dog was left in the car, to get a better idea of what we’re looking at here.

Left for a trip, leaving dog in car from midnight to 5pm, with 96 F during the day.
Oklahoma deputy left dog in car for 38 hours.
K9 died after 12 hours in direct sunlight.
Jola was trapped for more than 20 hours, during near triple-digit temperatures.

In all cases, we’re looking at a substantial amount of time.

The Great Outside

It looks like Phoenix may hit 115 degrees F this week, and many dogs live outside there without dying, one important difference being some access to water. However, I’ve tracked loose dogs during the summer, where their only real source of water was the early-morning sprinkler systems.

I believe there also was a time, many years ago, when a large number of people drove cars that were lacking air conditioning systems. I even remember a few of those, where traffic jams in the summer were brutal, especially with the wife and kids. However, I don’t believe very many of us died.

Looking at their chart, if it’s 95 F outside, they start the car from 95 F. However, these days many people will use their air conditioning, so the car may actually start from maybe 75 F, which gives you another 10 minutes.

Some Testing Results

I decided to try some simple tests, to see what happens. During the Summer, I tried with a white car. The temperature outside was 92F deg, with a hot sun, a very calm day, and at 5000 feet altitude. After 30 minutes in direct sunlight the temp inside the completely closed car varied by 30 degrees, from floor to ceiling. Except that the dash alone was 20 degrees hotter. But, we never really lay on the dash, nor do the dogs sit on the 130F deg ceiling. As to the 100F degrees on the floor, my dog was quite comfortable laying outside on the patio at that temperature.

I was very curious about all these experts concluding that the car windows had a minimal effect, without anybody at all ever noting the wind speed. Obviously, a hurricane would change that, but what about a 2 mph breeze?

Another test I did was similar, at a 94F temperature. For this one it was partly cloudy with the car partly under a tree. This time the windows were open over 3″, and we had about a 2-4 mph breeze. Returning after 30 minutes, the temperature at the car seat was 95F. Adding another half-hour, the temperature did not change.

While a few other variations might heat up either faster or slower, it seems to me that these give a fair representation of how much it might vary. If you researched some HVAC (Heating, ventilation, and air conditioning) websites, you would see how the speed and volume of airflow from the outside would impact the air exchange and temperature inside a room. While this is well-established science for many decades, none of those authorities publishing hot car temperature tables appear to be familiar with it.

Instead, some of the studies seem to go out of their way to specify even the car seat material, and the specific brand of thermometer used. But, little is said about the window opening, and nothing about the outside breeze. Most of the tests appear to be from medicine and a few other sciences. But none from a physicist or HVAC engineer.

Simplify, for Simple People?

I suppose that one possible explanation for their simple chart and advice is in keeping it all as simple as possible. That the testing results I gave might just be too complex for the majority of people to grasp. Or, perhaps too complicated for the article experts?

Another possibility is that they feel if you give more than the very worst case, too many people will assume it will never happen and just ignore your advice. However, with their extreme, some of that very issue is now happening. I’ve spoken to people where, just by checking their car temperature a few times, it becomes very obvious to them that the table is pretty bogus, so they mostly ignore it and possibly ignore a dangerous situation.

Way back and long ago, most humans were hunter-gatherers, who spent a great deal of time outside. And each time they left shelter people would have to take note of the temperature, wind, and sunlight. Perhaps these are lost instincts? At least among some scientists?

Sure, the weather may change after you park your car. The wind may die, the sun may come out, or the rain may be pouring down on your open convertible. Most people’s lives are not guided by what might happen, but by what they feel is likely to happen.

Finally, the Advice

Start by realizing that those charts are pretty much the worst case, but that it sometimes can be nearly that bad. In the first test I did above I ended up with 100 F on the floor. Say I moved that to a seat and made it 110 F, so let’s take that and look at similar and familiar situations.

Comparing this to summer in Phoenix, AZ, an outside dog might be spending hours at that temperature. Provided he has shade and enough water, we know he will survive, as thousands of them do each year.

If we walk our dog outside in the summer for an hour, he may be a bit thirsty back at home. But he is unlikely to pass out from thirst or suffer harm during the walk (assuming he’s walking on grass or dirt). And even a light breeze will help to cool him off.

If I’ve been running the air conditioning, the car will stay cool enough for at least 10 minutes..But, if not and I’m sitting in direct sunlight with still air, that combination leads to the worst-case situation, so you never want to leave that for long.

With these variables and uncertainties, time is likely the biggest factor. If sunny, I look for a shady spot, and leave all the windows open a few inches. If I expect to be more than a few minutes, I set the timer on my watch. Even on the worst day, I’ve got about 15 minutes which is long enough to quickly pick something up. How much longer I can take, simply depends on all the factors I mentioned above.

The Conclusion

There is certainly potential danger here, but extreme warnings from false experts who are ignorant of both thermodynamics and physiology may cause unexpected harm. When it is obvious their advice is wrong, many people will then simply discount it, instead of trying to take it partly into consideration.

At the other extreme, some people reading those charts will harass others for no good reason.

In the end, a great deal of common sense and consideration will be lost to these extremes. Some dogs will be saved from their effort, but other will suffer due to it. Extremes are rarely the best solution to any problem, and people should learn to deal with this in a reasonable manner.