Alternate entry procedures allow for employee entry into confined spaces so long as there are no safety (physical) hazards AND the atmospheric hazards can be controlled by continuous forced air ventilation. Under this type of entry, no permit, attendant or rescue provisions are required; however, a verification that the space is safe for entry and that pre-entry measures have been taken must be provided. 

While OSHA agrees that ventilation is the most important engineering control available to maintain a safe working environment. However, they do not provide guidance on ventilation methods, ventilation equipment or even how many air exchanges per hour must be provided for the space. Even though a common rule of thumb is 6 air exchanges per hour, some safety professionals and equipment companies recommend up to 10 or 15 exchanges. Remember that the number of air exchanges is not based on the size of the space but the atmospheric conditions in the space.

OSHA lists their basic consideration of hazardous atmospheres under the definition section of the PRCS standard along with the requirements to maintain an acceptable atmosphere.  Atmospheric testing must be done before the employee enters the space and periodically during the entry. The entrant must vacate the space immediately if a hazardous atmosphere is detected.

Written verification of the safe entry conditions and that pre-entry procedures have been conducted are required. This verification is done through a written certification that contains the date, location of the space and the signature of the person providing the certification. The certification and monitoring testing and results must be made available to the employee.

• 100 people die each year because of improper ventilation in permit spaces, 6000 are injured.
• Ensure that ventilators are used and maintained according to the manufacturer's directions.
• Always use the manufacturer's purge charts for initial ventilation time and retest conditions before entry.