If a door was wide open, and then halfway closed, by how much does the oxygen/air in the room get reduced?

It depends on the rate and volume of airFLO. ;-)

Is it without any other ventilation such as a heater vent?

@Brian1946 Good one!
I didn’t think of the rate of airflow. But let’s say the rate of airflow stays the same?

@snowberry If everything stays the same, ventilation etc.,

Great to see you Flo. We were worried about you!

^Same here. @flo, would you like to answer this roll call?

The amount of air in a room only changes by the volume of the door. With the door opened (swinging into the room) the amount of air in that room is reduces by that much.

The percentage of oxygen stays completely unchanged unless the room is completely sealed, in which case you’re more in danger of increasing CO2 concentrations than decreasing oxygen concentrations.

Antoine-Laurent de Lavoisier 26 August 1743 – 8 May 1794), also Antoine Lavoisier after the French Revolution, was a French nobleman and chemist who was central to the 18th-century chemical revolution and who had a large influence on both the history of chemistry and the history of biology. He is widely considered in popular literature as the “father of modern chemistry”.

It is generally accepted that Lavoisier’s great accomplishments in chemistry stem largely from his changing the science from a qualitative to a quantitative one. Lavoisier is most noted for his discovery of the role oxygen plays in combustion. He recognized and named oxygen (1778) and hydrogen (1783), and opposed the phlogiston theory. Lavoisier helped construct the metric system, wrote the first extensive list of elements, and helped to reform chemical nomenclature. He predicted the existence of silicon (1787) and was also the first to establish that sulfur was an element (1777) rather than a compound.He discovered that, although matter may change its form or shape, its mass always remains the same.

Lavoisier was a powerful member of a number of aristocratic councils, and an administrator of the Ferme générale. The Ferme générale was one of the most hated components of the Ancien Régime because of the profits it took at the expense of the state, the secrecy of the terms of its contracts, and the violence of its armed agents. All of these political and economic activities enabled him to fund his scientific research. At the height of the French Revolution, he was charged with tax fraud and selling adulterated tobacco, and was guillotined.

If you have eliminated air flow as a variable, the oxygen in the room would remain the same. You basically made it a stagnant system. If you add people to the room, the oxygen would be reduced by whatever the person are using to live.

It is somehow comforting to see that you haven’t changed a bit. To begin with why should the oxygen level in a room increase or decrease whether the door is open or closed? There is once again no sensible answer to this question due to the way it is worded. The air will flow either into the room or out of the room with the door open, but just because the air is flowing, there is no reason to suspect that there should be more or less of it anywhere in the room regardless of the direction or rate of flow.

Even before COVID, we let the unclean air out and the fresh air in by opening the door/ window whenever weather allows.

By the way I just went to the roll call thread @Brian1946, thanks for the invitation.

If there is smoke in your house, or if using certain chemicals do you not open the windows?

But just look at your question flo and think about all the things missing in order to calculate a reasonable answer. Are all the doors or rooms in the world the same size? Will the air flow in or out of the room at same rate every time? Opening the door or window does not “reduce”
the air. It merely brings the room into equilibrium with the atmosphere exterior to the room. And finally, not only are dimensions and flow rates excluded from your question, the factor of time allowed in the process is completely ignored.

Consider the air as a liquid. If there is a way for the air to get in and the area in question is full of air, the volume/pressure remains the same, except for the displacement of the door, if it swings into the room.

Let me just add:
https://tinyurl.com/y4t5anre (Google “open the windows and let in the fresh air in”)

“It is an obvious solution, but it works. “Fresh air isn’t the enemy. Open your windows,” says Dr Appelles Econs, an allergy specialist at the Burghwood Clinic. Keeping your windows shut all day will allow chemicals and allergens to build up inside.

Even if you live in a polluted city, you are going to have to open the windows from time to time. “You don’t want to be stuck in a house with no ventilation all day,” says Dr Paul Young of Lancaster University.”
https://www.theguardian.com/lifeandstyle/2020/apr/05/open-your-windows-and-four-other-ways-to-improve-the-air-quality-at-home

Thanks. @Brian1946 @snowberry @filmfann @Caravanfan @doyendroll @seawulf575 @kritiper

I kind of see what you mean re. if there is no airflow.