Pulling the nearest fire alarm is the most efficient method of notifying persons in your facility. The nearest city fire department will respond. Have someone meet the Fire Department outside when they arrive. Opening windows in negative pressure locations pulls air into the room, in an attempt to equalize the room's pressure with the atmospheric pressure. Since the remainder of your building will still be at a negative pressure, the air and any odor in the room with the open window will be drawn into the hallways and other common areas and spread throughout the building.
Drains have vents to the outside atmosphere.
Therefore the plumbing in buildings which have negative pressure as compared to outside, can serve as a port for drain or sewer gases when a sink trap has dried out or the plumbing is in disrepair. It is important to maintain plumbing integrity and to keep water in the traps to prevent entry of nuisance odors from this source. At least once per month, if a sink or floor drain is not being used, you should run water for 10-15 seconds. Contrary to old recommendations, running water for a minute or more does nothing but waste water. Don't forget to take care of ALL the drains in your location, including floor drains, cup sinks and sinks in your hoods.