Availability of ventilation
Three levels of availability of ventilation should be considered
Good
Ventilation is present virtually continuously
Natural ventilation which is generally obtained outdoors, is considered to be good when the wind speed is greater
than 0.5 m/s (approx 1.1 miles per hour)
Fair
Ventilation is expected to be present during normal operation. Interruptions are permissible provided that they occur
infrequently and for short periods.
Poor
Ventilation, which does not meet the standard of fair or poor, but interruptions are not expected to occur for long
periods. Ventilation, which is less than poor, is ignored.