Closing doors and windows is not easy to lack oxygen.
How much oxygen will people consume when they sleep?
First, let's calculate how much oxygen people consume when they sleep. A concept of metabolic equivalent is introduced here: MET.
Qiu Junqiang, Yang Junchao and others published a paper "Reference Value of Physical Activity Energy Consumption of Healthy Adults in China" in China Journal of Sports Medicine.
It is mentioned that 1MET is defined as resting metabolic rate, that is, the amount of oxygen consumed by sitting quietly in a chair is about 3.5ml/kg/min.
When sleeping, it is about 0.9MET, that is to say, if a 65kg adult sleeps in the car for 8 hours, the oxygen consumption is about109.2l.
How much oxygen is in the car? Is there enough oxygen in the car after sleeping all night?
Generally speaking, the total volume of the interior space of a car is 3.5m? About, that's about 3500L l, the normal content of oxygen in the air is about 2 1%, and the oxygen in the car is 735 l.
After a night's sleep, the oxygen consumption in the car is109.2l. At this time, the oxygen content will probably drop from 2 1% to 17.8%.
In GB8958-2006, the definition of hypoxia is that the oxygen content in the air in the workplace is lower than 19.5%.
17.8% oxygen content is more dangerous, that is to say, if there is no outside air to enter, sleeping in the car for one night may indeed lack oxygen.
Even if the doors and windows are closed, the outside air can enter.
However, it should be noted that there was a big premise just now: that is, no outside air entered. But in fact, even if the doors and windows are closed, it doesn't mean that the outside air can't enter.
First of all, some models will automatically switch to the external circulation after flameout, which is equivalent to reserving an air inlet.
For example, the owner's manual of Toyota Fangrong is translated as follows: When parking, the system will automatically switch to the mode of external air circulation to achieve better air circulation of the whole vehicle, which will help reduce the odor generated when the vehicle starts.
In addition to Toyota, Nissan Qi Jun, Buick Regal and other models will also automatically switch to the external cycle. And even if the external circulation is not switched, the car is not completely sealed.
Wang Fuliang published a paper "Evaluation of the Influence of Pressure Reducing Valve on Ventilation Flow and Pressure in Passenger Compartment" in the magazine of Automobile Safety and Energy Saving.
It says: the passenger compartment exchanges air with the surrounding environment through the opening on the car body.
What do these vacancies include? Listen: interior trim panel/instrument panel gap, front and rear side door gap, skylight gap, trunk/tailgate gap, pressure reducing valve.
Simply put, there are still some gaps in every breathing part of the car, just like sleeping in a room. When the doors and windows are closed, air can still enter and exit through various gaps.
There is also a test: when the pressure in the car is 125Pa, even if the pressure relief valve is closed, the ventilation volume is 8 1L/s only by the gap in the car.
When sleeping and breathing, the pressure is about 0. 133 to 0.266kPa, which is actually a little higher than the pressure tested in the paper.
So in fact, even if you close the doors and windows and sleep in the car for one night, it is not easy to lack oxygen.
If you turn on the air conditioner to sleep, there will be hypoxia.
Speaking of which, in order to sleep more comfortably, it is hot and cold. Do you turn on the air conditioner? At this time, there may be danger.
Shenzhen Special Zone Daily reported a case in 2020: In Baoan District, Shenzhen, a woman rested in her car with air conditioning on and died unexpectedly.
Later, the doctor speculated that the woman died of carbon monoxide poisoning and suffocation.
Engine idling will produce a lot of carbon monoxide.
If the car has been running over there, the air conditioner is turned on when sleeping, and the engine has been idling, it is easy to produce a lot of carbon monoxide gas at this time.
Wang Luting of Beijing Jiaotong University has a master's thesis "Study on the Impact of Idle Vehicle Emissions on the Atmospheric Environment of Residential Areas".
It says so: when the motor vehicle is idling, the engine is poor in oxygen and rich in combustion, and the concentration of hydrocarbons and carbon monoxide emitted by the motor vehicle is obviously higher than other working conditions.
It's like burning an old earthen stove with a lot of firewood. Resulting in insufficient oxygen and insufficient combustion. Is there a lot of cigarettes? There is a lot of carbon monoxide in it.
Carbon monoxide entering the car will lead to lack of oxygen.
If the place where you just parked and slept is relatively closed and the exhaust gas can't be dispersed, it will always be around the car.
These air with high concentration of carbon monoxide will cause the oxygen content in the car to drop rapidly after entering the car.
Pan Jin and Chen Chuanju published a paper "Monitoring of Carbon Monoxide Concentration in Cars and Design of Emergency System" in Journal of Yellow River Institute of Science and Technology.
There are experimental data in it: park the vehicle in a closed garage, close the doors and windows, and measure that the carbon monoxide content in the vehicle is 0mg/kg and the oxygen content is 2 1%.
Start the vehicle, turn on the vehicle air conditioner, and measure again after 10 minutes. The carbon monoxide concentration in the car is 24mg/kg, and the oxygen concentration is 15%, which is considered as an anoxic environment.
A closed garage like this, 10 minutes, is dangerous.
Without air conditioning, it is not easy to lack oxygen.
So generally speaking, if you don't turn on the air conditioner and sleep like this, even if you close the window, you will be fine all night, and it is not easy to die or lack oxygen.
However, if the air conditioner is turned on, the exhaust gas from the engine will cause a large amount of carbon monoxide to gather in the parking space and enter the car, and the amount of oxygen will drop sharply, leading to various situations such as hypoxia and suffocation, and problems will arise.