The only way in which a room can be kept fit for human beings to breathe in is to have a draught, or current of air, pouring into it through open windows, or open doors, or ventilating shafts, at least as rapidly as it is being breathed by the persons who occupy that room.

By hundreds of tests this has now been found to be on an average about four bushels a minute for each person, and any system of proper ventilation must supply this amount of air in order to make a room fit to sit in.
If a man, for instance, accidentally gets shut into a bank-vault, or other air-tight box or chamber, it will be only a few minutes before he begins to feel suffocated; and in a few hours he will be dead, unless some one opens the door.

A century ago, when the voyage from Europe to America was made in sailing vessels, whenever a violent storm came up, in the smaller and poorer ships the hatches were closed and nailed down to keep the great waves which swept over the decks from pouring down the cabin-stairs and swamping the ship.

If they were kept closed for more than two days, it was no uncommon thing to find two or three children or invalids among the unfortunate emigrants dead of slow suffocation; and many of those who were alive would later have pneumonia and other inflammations of the lungs.

On one or two horrible occasions, when the crew had had a hard fight to save the ship and were afraid to open the hatches even for a moment, nearly one-third of the passengers were found dead when the storm subsided.