Environmental, Health and Safety Services

Confined Spaces Hazards

The presence of any of the hazards listed below deems the confined space a permit-required confined space. Permit-required confined spaces are hazardous and must not be entered at Virginia Tech unless all necessary precautions have been implemented. Permit-required confined spaces can be declassified, or reclassified, to non-permit-required confined spaces under certain conditions, such as when engineering controls are implemented or hazards are eliminated prior to entry.


Hazardous atmospheres are the leading cause of deaths in confined spaces. This condition is often difficult to detect without proper air monitoring equipment. The lack of natural ventilation, the presence of stored materials (such as chemicals), or the work process to be performed in a confined space can result in one or more of the following hazardous atmospheres.

Oxygen-deficient atmospheres

An oxygen-deficient atmosphere has less than 19.5% available oxygen. Any atmosphere with less than 19.5% oxygen shall not be entered without appropriate ventilation or supplied air respiratory protection.

The oxygen level in a confined space can decrease because of:

  • Work performed, such as welding, cutting or brazing
  • Certain chemical actions or reactions (for example, the rusting of metal)
  • Bacterial action
  • Displacement by another gas, such as carbon dioxide or nitrogen.

Oxygen-enriched atmospheres

An oxygen-enriched atmosphere has more than 23.5% oxygen content, and can result in fires that burn more violently. The oxygen level can increase because of pure oxygen leaks from compressed gases associated with welding and cutting activities in a confined space.

For an atmosphere to be flammable, there must be adequate oxygen in the air and a flammable gas, vapor, or dust present in the proper proportion. Different gases have different flammable ranges. If a source of ignition (such as a sparking or electrical tool) is introduced into a space with a flammable atmosphere, an explosion will result.

Flammable atmospheres

A flammable atmosphere may be present when oxygen and a flammable gas reach certain concentrations in the presence of an ignition source. Sources of flammable gases may come from leaking acetylene hoses, methane gas, chemicals or other products used in the space. As a precaution, entrants must not enter a space where the Lower Explosive Limit (LEL) equals or exceeds 10%. If the LEL shows a percentage less than 10%, but greater than 1% or 2%, it would be prudent to investigate possible sources prior to entry

Toxic atmospheres

Toxic substances can come from the following:

  • A product stored in the space. Refer to the Safety Data Sheet for the product for product-specific information.
  • The work being performed in the space. Examples include welding, cutting, brazing, painting, scraping, sanding, degreasing, use of solvents, etc. Refer to the Safety Data Sheet for product-specific information.
  • Toxic materials stored in areas adjacent to the confined space. Examples include chemicals or fuel stored in leaking underground storage tanks, or sections of the steam tunnels that may overlay or lie adjacent to a leaking sewer system.
  • Rotting or decaying materials which create toxic gases, such as hydrogen sulfide or nitrogen dioxide (i.e. silo gas).
  • Carbon monoxide created from incomplete combustion of a fuel or microbial decomposition of organic matter.


Steam Tunnel

Many campus confined spaces, such as the steam tunnels and large ovens, may have greatly elevated temperatures which can increase the risk of heat stress or heat stoke. Heat stress conditions exist when high temperatures and humidity and limited air movement are present. Other factors include direct sun or heat sources, physical exertion, poor physical condition or medications taken by an individual, or an inadquate tolerance for hot workplaces. Prevention is the best strategy, and information regarding signs and symptoms, as well as recommended practices are included in training, such as adequate ventilation, frequent breaks, increased fluid intake, or the use of cooling vests and similar products.

Energy Sources

Hazardous energy sources in VT confined spaces typically include high voltage, steam, or mechanical hazards. For more information on hazardous energy and Virginia Tech's Lockout/Tagout Program, click here. The hazardous energy must be isolated or removed from service prior to entering the space. The energy control method used must completely protect employees from the release of energy or materials into the space. This is accomplished by:

  • Blanking, blinding, misaligning or removing sections of lines, pipes or ducts;
  • A double block and bleed system;
  • Lockout/tagout of all sources of energy, including mechanical, electrical, chemical, pressurized systems, thermal (e.g. uninsulated systems which operate at a temperature, either hot or cold, that could cause physical injury upon contact) or gravity (for example, elevated platforms that could shift and then lower upon an entrant);
  • Blocking or disconnecting all mechanical linkages to prevent movement.


Feed Bins

The space could have an internal configuration that could trap an entrant, e.g. inwardly converging walls or a floor that slopes downward and tapers to a smaller cross section. The atmosphere at this bottom cross-section may be hazardous, or there may be mechanical hazards (e.g. augers) which could seriously injury or incapacitate the entrant. Examples of possible engineering controls to eliminate exposure include lockout/tagout, temporary floorings, and mechnaical ventilation.



Engulfment means that finely divided solids (e.g. grains or sand) or liquids are stored in a space that could surround and suffocate an entrant. Death could result from the material filling or plugging the respiratory system or the weight of the material crushing or constricting the chest to the point that respiration is difficult or impossible.


Other serious hazards may include inherent fall hazards, use of hazardous chemicals or degreasers, or performing welding and cutting in a confined space. Hazards must be evaluated by the Entry Supervisor and necessary controls implemented to eliminate or isolate the potential hazard.