A confined space has these characteristics:

  • Is large enough to allow an employee to enter and perform work
  • Has limited or restricted means for entry or exit; and
  • Not designed for continuous human occupancy

A permit-required confined space has the above characteristics as well as one or more of the following characteristics:

  • Contains or has the potential to contain a hazardous atmosphere
  • Contains a material that has the potential for engulfing an entrant
  • Has an internal configuration such that an entrant could be trapped or asphyxiated by inwardly converging walls or by a floor which slopes downward and tapers to a smaller cross-section
  • Contains any other recognized serious safety hazard.


Confined spaces that have serious or potential hazards must be identified and are classified as permit-required confined spaces.   The Environmental Compliance Branch maintains an inventory of permit-required areas.  Employees are made aware of these spaces by warning signs posted at each entrance.  See Attachment 2 for a current inventory.

Under this program confined spaces include, but are not limited to tunnels, crawl spaces, air plenums, ceiling crawl spaces, attics, storage tanks, utility vaults, sewers,  pits, ventilation or exhaust ducts, pipelines, boilers, acid neutralization tanks, sand and grease traps, manholes, water shut off pits, air handling units, cooling towers, kilns, and window wells.

 The crawl spaces and tunnels have been inspected and tested using an air monitor to determine safe entry procedures.   Under normal working conditions, it has been determined that these areas are safe to enter without additional air monitoring due to the passive ventilation systems in tunnels and crawl spaces.  However, to ensure means of egress from the tunnels and crawl spaces all tunnel access hatches must be kept clear at all times.

Work practices such as welding, cleaning with solvent, or painting can significantly change the conditions of or in these areas.  When activities such as these are performed, these areas become permit-required confined spaces and the permit-required confined space entry procedures must be followed.

Hazard Evaluation for Confined Spaces

All potential hazards of the confined space are identified and evaluated.  A trained Environmental Compliance Branch employee or designee is required to test the atmosphere in the space before and during entry, if the potential for a permit-required atmosphere hazard exists in the space.  The tests, done with a calibrated direct reading air monitor for oxygen content, flammable gases, carbon monoxide and carbon disulfide.  Physical hazards to inspect include unguarded machine parts, heat sources, exposed electrical circuits, slip/trip/fall hazards, noise, lighting, wind, water, and biological hazards (molds, rodents, snakes, and spiders).  Documentation of the confined-space entries and associated air monitoring results are recorded on the pre-entry checklist and maintained in the Environmental Compliance Branch office.

Preventing Unauthorized Entry

Warning signs posted at entrances identify permit-required confined spaces.