Friday, May 10, 2013

Confined Space Procedures

Confined Space.

Confined space defined as a place where the means of entry or exit are restricted because of location, design, construction or contents. It may include tanks, tankers, tunnels, silos, sewers, flues, pipelines, sea containers or vessels. The main hazards encountered in confined spaces are fire or explosion, asphyxiation, toxicity, drowning in liquids or free flowing solids and injury or death if mechanical equipment within the confined space is inadvertently turned on while someone is still inside. These hazards are due to the presence of hazardous gases, vapours, fumes, dusts or the creation of an oxygen-deficient or oxygen-rich atmosphere.

Hazards in a Confined Space

Every confined space must be evaluated (with the help of Multi Gas Detector) for these four types of hazards.
  1. Oxygen-deficient atmospheres 
  2. Flammable atmospheres 
  3. Toxic atmospheres 
  4. Mechanical and physical hazards.
The three types of atmospheric hazards are often the most difficult to identify since they might not be detected without the assistance of a Multi Gas Detector.

The following must also be done when using the alternate procedures:

  1. Ensure safety before removing a cover and guard opening immediate.
  2. Test internal atmosphere (With the help of Multi Gas Detector )(Oxygen, Flammables, Toxins) - observation available to entrant
  3. Continuous forced air ventilation
  4. Atmosphere periodically tested - observation available to entrant
  5. Evacuate immediately if necessary and evaluate what went wrong
  6. Verify these procedures were conducted through a written certification
There must be documentation detailing that the space is safe for entry and the pre-entry measures were conducted. This ‘certification’ must contain the date, location of the space, and signature of the person making the verification. The certification must be made before entry and must be made available to all entrants or to their authorized representative(s).

Oxygen-deficient atmospheres

The normal atmosphere is composed of approximately 21% oxygen and 79% nitrogen. An atmosphere containing less than 19.5% oxygen is considered oxygen-deficient (Ref: Appendx-04). The oxygen level inside a confined space may be decreased as the result of either consumption or displacement.

Oxygen Level
Minimum acceptable oxygen level
15 - 19%
Decreased ability to work strenuously.
Impair coordination. 
Early symptoms.
Respiration increases.  Poor judgment.
Respiration increases.  Lips BLUE.
Mental failure.  Fainting. Nausea, Unconsciousness. Vomiting.
8 minutes - Fatal, 
6 minutes - 50% fatal                                     
4-5 minutes - possible recovery
Coma in 40 seconds.  Death

Flammable atmospheres

Fire or explosions may occur in confined spaces which have
An atmosphere within the explosive limits of the gas (or liquid vapour). Explosive limits (also known as ‘flammable limits’), expressed in percentage, may be defined as the minimum and maximum concentrations of a flammable gas or vapour between which ignition can occur. Concentrations below the lower explosive limit (LEL) are too lean to burn while those above the upper explosive limit (UEL) are too rich.

Explosive/Flammable Limits, Fire and explosion prevention

Work where a flame is used or a source of ignition may be produced (hot work) should not normally be performed in a confined space unless:

All flammable gases, liquids and vapours are removed prior to the start of any hot work. Mechanical ventilation is usually used to:

  1. Keep the concentration of any explosive or flammable hazardous substance less than 10% of its Lower Explosive Limit AND 
  2. Make sure that the oxygen content in the confined space is not enriched. Oxygen content should be less than 23% but maintained at levels greater than 18%.
Surfaces coated with combustible material should be cleaned or shielded to prevent ignition:

While doing the hot work, the concentrations of oxygen and combustible materials must be monitored to make certain that the oxygen levels remain in the proper range and the levels of the combustible materials do not get higher than 10% of the Lower Explosive Limit. In special cases it may not be possible, and additional precautions must be taken to ensure the safety of the worker prior to entering the confined space.

If a potential flammable atmosphere hazards are identified during the initial testing, the confined space should be cleaned or purged and ventilated, and tested again before entry to the confined space is allowed. Only after the air testing is within allowable limits should entry occur, as the gases used for purging can be extremely hazardous.

Toxic atmospheres

Toxic atmospheres may be present within a confined space as the result of one or more of the following:
  1. The product stored in the confined space. When a product is stored in a confined space, the product can be absorbed by the walls and give off toxic vapours when removed or when cleaning the residual material. The product can also produce toxic vapours that will remain in the atmosphere due to poor ventilation.
  2. The work being conducted in the confined space. Examples of such work include: welding or brazing with metals capable of producing toxic vapours, painting, scraping or sanding. Many of the solvents used for cleaning and/or degreasing produce highly toxic vapours.
  3. Areas adjacent to the confined space. Toxic fumes produced by processes near the confined space may enter and accumulate in the confined space. For example, if the confined space is lower than the adjacent area and the toxic fume is heavier than air, the toxic fume may ‘settle’ into the confined space.
Effect 0f Hydrogen Sulfide (H2S).          
Permissible Exposure Level
8 Hours
50 – 100
Mild Irritation - eyes, throat
1 Hour
200 – 300
Significant Irritation
1 Hour
500 -700
Unconsciousness,  Death
1/2 - 1 Hour
Unconsciousness,  Death

Effect 0f Carbon Monoxide (CO).

Permissible Exposure Level
8 Hours
Slight headache, discomfort
3 Hours
Headache, discomfort
1 Hour
Confusion, nausea, headache
2 Hours
Tendency to stagger
1  1/2 Hours
Slight heart palpitation
30 Min.
30 Min


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