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Confined Space Entry

June 17, 2014

Confined Space Entry

The material in this post is extracted from Chapter 3 – Energy Control Procedures – of the book Plant Design and Operations.

A Confined Space is a space which is large enough for a worker to enter but has limited openings for entry and exit and is not intended for continuous employee occupancy. Entry is considered to have occurred as soon as any part of the entrant’s body breaks the plane of an opening into the space. Therefore it is not permissible, for example, to take a quick breath and to put one’s head into a vessel for a quick look without having an entry permit. Wherever possible work should be organized such that it can be carried out without anyone needing to enter the confined space. If someone does need to enter the confined space the most rigorous controls and procedures must be followed.

Confined spaces include, but are not limited to, storage tanks, towers, drums, boilers, furnaces, sewers, ventilation and exhaust ducts, underground utility vaults, manholes, pipelines, excavations and pits. A confined space is not the same as anenclosed space. Therefore most pipeline trenches are also considered to be confined spaces, even though they are open to the atmosphere. A person working in a trench could be trapped by falling materials or overcome by fumes from a leak. He or she cannot easily escape since they will have to climb out of the trench, probably using a temporary ladder. Entry onto the roof of an external floating roof tank when the roof is more than one meter below the top of the shell also constitutes entry into a confined space.

A confined space should be big enough for a person to enter bodily. A small box such as a metering station may contain hazards such as venomous animals. However, since a person cannot enter with his or her whole body they would not normally be considered as confined space (although some legal interpretations may differ).

Sometimes it is not always clear when a space should be treated as “confined”. On one marine vessel, for example, a worker entered a room containing equipment and was fatally overcome by fumes. It is likely that he thought of the room as being part of the normal work space and so no special precautions were needed.

Confined spaces are classified as either hazardous or non-hazardous. A hazardous space is one that is known to contain a hazardous gas. The gas could be inert (such as nitrogen), toxic (such as hydrogen sulfide) or flammable (such as methane). A non-hazardous space is one that has been purged with air such that a person entering the space does not need breathing apparatus. However, before a person enters a non-hazardous space the atmosphere in that space must be tested for oxygen, and must be re-tested on a frequent or continuous basis. Similarly tests should be conducted for the presence of hazardous gases. The test instrument should be at the same location as the person performing the work.

The following general guidance should be considered when planning confined space work in a vessel.

  • Prior to approving personnel entry, the vessel must be positively isolated by blinding or disconnecting all connections to the vessel, except the purge gas connection, to prevent accidental contamination of its inert atmosphere during entry by personnel. Where blinding or disconnecting piping is not feasible, e.g.,welded piping systems, a double block and bleed system may be have to be considered.
  • Maintain a list of authorized entrants, designate an entry supervisor, and provide a means to prevent unauthorized entry.
  • Energized equipment must be brought to a safe energy state, locked/tagged out, and radioactive sources must be shielded and locked/tagged out, or removed.
  • Prior to entering an inerted confined space, conduct tests to determine oxygen content, and % Lower Explosive Limit (LEL) of the atmosphere at conditions which are as close as reasonably possible to the actual entry conditions and with all service equipment operating.
  • The oxygen content of the atmosphere within the vessel must be monitored continuously with equipment capable of recording low oxygen levels.
  • The temperatures within the vessel must be monitored continuously.  If any temperature rises 10°C (above normal day/night variations), personnel must leave the vessel until it is assured that their safety is not jeopardized due to an exothermic reaction or other such potentially harmful situations.
  • Standby personnel and rescue equipment must be available at the confined space entry point. The rescue equipment must be assembled and ready for use.  Rescue personnel must be trained in the proper use of this equipment.

Types of Space

Confined Space EntryConfined space entry can be divided into two broad areas: non-hazardous spaces which have been ventilated and hazardous spaces that are known to contain hazardous materials.

Non-Hazardous Space

Before a person can enter a non-hazardous confined space the following conditions must be met:

  • It must be shown that the work cannot be accomplished from the outside.
  • The oxygen content must be in the range 19.5 to 23.5%.
  • The flammability level must be below 10% LEL.
  • There are no toxic gases in the confined space.
  • The space does not contain grain, sand or other solid material that could flow and engulf a worker.
  • The temperature in the confined space should be normal. If the space was purged with steam prior to entry it should be cooled down.
  • Noise should be controlled. Confined spaces can be very noisy because of the echoes that are generated.
  • The equipment being worked on is properly isolated.

Hazardous Space

A hazardous confined space is defined as containing, or having the potential to contain, “a recognized serious safety or health hazard”, in other words the space is known to contain hazardous materials and therefore the workers entering that space must wear protective clothing and breathing apparatus. Such as space will meet one of more of the following conditions.

  • An oxygen concentration less than 19.5% or greater than 23.5% and/or maintained inert by gas purging.
  • Lower explosive limit (LEL) greater than 10%. If the confined-space atmosphere exceeds 10% LEL then additional ventilation is needed, or the space must be inerted prior to entry. The need for continuous mechanical (forced) ventilation should be determined on a case-by-case basis and noted on the permit.
  • An atmospheric concentration above the permissible exposure level (PEL) of a toxic substance or an atmospheric concentration of any substance that is immediately dangerous to life or health, (IDLH).
  • An airborne combustible dust at a concentration that exceeds its lower flammable limit (LFL).
  • A confined space that contains a material that could physically engulf the entrant.
  • A confined space that has an internal configuration such that an entrant could be trapped or asphyxiated by inwardly converging walls or floor which slopes downward and tapers to a smaller cross section.

Extraordinary precautions are necessary for entry into a hazardous confined space due to the inherent danger. Special precautions include, training of all participants, assigning an outside attendant, maintaining a list of authorized entrants, assigning an entry supervisor, the provision of breathing air and the use of retrieval systems.

One special type of hazardous space is one where the atmosphere in a vessel must be kept inert because the vessel contains special chemicals or catalysts that would be damaged or could catch fire if exposed to oxygen. Special written job procedures, detailed planning, and training prior to entry must be developed and followed to perform this work safely and efficiently.

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