Indoor gas leaks: Ventilate
The incident commander should coordinate with the local gas utility representative before ventilating a building.
Exercise extreme caution when ventilating a building with natural gas concentration above 15 percent. As the gas dissipates and the concentration decreases, the amount of gas in the air will drop toward the flammable range between 5 and 15 percent. Remove all possible ignition sources before proceeding with ventilation.
When it is determined that ventilation is safe, ventilate the building from the top down, using natural air currents.
Artificial or forced ventilation is not usually necessary. However, if power ventilation is needed to clear the structure, use intrinsically safe ventilators and positive pressure ventilation on the upwind side. Be careful not to exhaust the gas into adjacent structures.