Smoke from a smoke tube can be used to observe airflow between areas or airflow patterns within an area.

To check the negative pressure in a room, hold the smoke tube near the bottom of the door and approximately 2 inches in front of the door, or at the face of a grille or other door opening. Generate a small amount of smoke by gently squeezing the bulb.

This test must be performed outside the room with the door closed. The smoke tube should be held parallel to the door, and the smoke should be issued slowly from the tube to ensure that the velocity of the smoke does not overpower the air velocity. The smoke will travel in the direction of airflow.

If the room is at negative pressure, the smoke will travel under the door and into the room (e.g., from higher to lower pressure). If the room is not at negative pressure, the smoke will be blown outward or will remain stationary.

If there is an anteroom, release smoke at the inner door undercut, with both anteroom doors shut.

In addition to a pedestrian entry, some isolation rooms or areas are accessed through a wider wheeled-bed stretcher door. Release smoke at all door entrances to isolation rooms or areas.

If room air cleaners are being used in the room, they should be running during the test.

Because the smoke is irritating if inhaled, care should be taken to prevent direct inhalation from the smoke tube. However, the quantity of smoke issued from the tube is minimal and is not detectable at short distances from the tube.