CONFINED SPACE

CONFINED SPACE ENTRY

1.0       Introduction

A confined space is defined as; any space that can fully encompass a person entering it and has restricted or limited air. Examples are; tanks, vessels, pits, hoppers, pipelines, shafts, etc.

2.0      Permits to Work

A Permit to Work and a Gas Test Certificate, should always be used for entry into any confined space.

3.0       Isolations

Electrically operated items in or connected to a vessel should always be isolated prior to entry. Actions include:

a)   Lock off motors

b)   Attach electrical isolation tags.

c)    Enter details of isolations on the Permit To Work.

Individual isolations of vessels is always the safest method. If this is not practical, adjacent vessels may be grouped together and isolated using valve isolation or slip plates. If this method is used, the valves should be locked off in the closed position.

Vessels not previously in use should be inspected for toxic coatings, corrosion, inhibitors, etc. The possibility of oxygen deficiency is always present especially when a vessel has been closed for some time.

If a manhole or similar opening must be left open prior to entry the cover should be temporarily replaced or some other suitable form of protection put in place to prevent people inadvertently falling into or entering the vessel.

When entry into a confined space is required, a vessel for example, the vessel must first be removed from service and isolated from all sources of liquid, fume, electrical and mechanical power. Consideration is to be given to the provision of access and egress, stand?by personnel, rescue needs and protective clothing and equipment.

4.0       General

Before entering a vessel/confined space, remove all residual materials (pump or drain) as completely as possible. Flush the vessel/confined space with water or an appropriate cleaning solution and follow with a final water flush.

Mechanically ventilate through introduction of fresh air. Be certain the ventilation intake air source is fresh and not contaminated.

Never use oxygen as a means of air supply as it creates a fire and explosion hazard.

Block off all piping through which toxic or potentially harmful materials can be introduced, by one or all of the following methods:

a)  Blank off entering line.

b)  Disconnect piping.

c)  Remove a section of piping.

d)  Lock off valves where it is not possible to perform any of the above procedures.

Immobilize powered equipment, prior to entry by one or more of the following methods:

a)  Physically lock out all electrical power at the circuit breaker box.

b)  Physically disconnect all mechanical drives to any powered equipment.

c)  Disconnect all hydraulic power supply lines.

5.0       Atmosphere Testing

The confined space must be tested for hazardous, toxic/flammable material and oxygen content. If conditions cannot be guaranteed, then thought should be given to the type of protective equipment which should be used. Atmosphere Testing should always be carried out prior to personnel entering a confined space.

A test for oxygen content to 21%, should always be done. If a lower reading is found, entry should not be allowed without protective equipment. If a higher reading is found, this indicates an oxygen enriched atmosphere, entry should not be allowed until the space has been purged.

Atmosphere testing is mandatory prior to any employee entering a vessel/confined space. When performing the test from inside the confined space, breathing apparatus must be worn until the atmosphere has been proven safe. 

Tests should be conducted throughout the confined space with special attention to potential "dead" circulation areas.

Instructions accompanying atmosphere test instruments should be thoroughly reviewed to ensure competent operation and correct interpretation of readings. Prior to actual testing, calibrate the portable multi gas (oxygen, combustible gas) to make certain it gives accurate readings.

Utilize the properly calibrated oxygen indicator to determine if the atmosphere is breathable.

Testing for oxygen must be done first to assure subsequent combustible gas measurements are reliable.

If prior oxygen testing indicates very little, or no oxygen present, the combustible gas measurements are not reliable. Adequate ventilation must be provided. Ensure normal oxygen levels are present before carrying out another combustible gas test.

In the unlikely event hydrogen or hydrogen-helium mixtures are present in the atmosphere, the instrument must be specially calibrated for hydrogen otherwise it will read erroneously low.

If toxic vapors are present in a confined space, the concentration must be evaluated in parts per million (PPM) in relation to the toxic substance threshold limit value (TLV) prior to employee entry.

If specific toxic substances are known or suspected to be present, proper tests specific for that substance must also be conducted.

Prior to entry, the confined space must be classified into one of the following Hazard Groups .

1)  Hazard Group A:

a)   Oxygen content is between 19.5% and 24% by volume.

b)   Combustible gas concentration is less than 20% of the lower explosive limit (LEL).

c)    Toxic vapor concentration is less than the threshold limit value (TLV) as indicated by the Polytest tubes, or for any specific material tested.

Restrictions

i.   No welding or burning is permitted unless the LEL is and remains below 5%.

ii.   If welding or burning is conducted, make certain ventilation is adequate both to remove welding fumes and to replenish oxygen consumed by combustion

iii.   Maintain air circulation to provide adequate air flow rates. Do not allow limited air circulation, air should enter through the bottom or side of the confined space and exit out the top or other side.

2)  Hazard Group B:

a.    Combustible gas concentration is less than 20% of the lower explosive limit (LEL).

b.    Oxygen content is below 19.5% by volume.

c.    Toxic vapor concentration is above the threshold limit value (TLV) as indicated by the Polytest tubes for any specific materials tested.

Restrictions

 i.   Approved breathing equipment must be operable and worn by all personnel entering the confined space. Do not recharge air cylinders or provide air through an airline from a compressor unless an in-line CO monitor, with alarm, is in use.

  ii.   No welding or burning is permitted unless the LEL is and remains below 5%.

3)  Hazard Group C:

Under no circumstances will a confined space be entered if the concentration of combustible gases cannot be maintained below 20% of the lower explosive limit (LEL).

EHS Requirements

A qualified standby-man must be in attendance for all confined space entries. His duties include:

a)   Maintaining visual and voice contact with personnel inside vessel/confined space, and

b)   Attending rescue lifelines and airlines. An approved safety belt with lifeline attached or another appropriate device must be used by all personnel entering a confined space. When conditions are such that personnel are required to wear respiratory equipment, there should be an additional team member whose sole job is maintaining radio contact. In the unlikely event of an accident the emergency response team would be called into action by radio contact.

Artificial Respiration

A person qualified in the use of artificial respiration and resuscitators is required to be in attendance at all times. A resuscitator must be on site at all times.

Rescue

a.    If entry is made in a hazard group B confined space, sufficient rescue personnel, equipped with approved operable breathing apparatus, are required to stand by.

b.    Rescue lifelines of sufficient length, being properly attached to personnel harnesses, are required.

6.0       Monitoring

The atmosphere should be tested at least every thirty minutes, or more often if warranted, to assure safe working conditions are maintained.

7.0       Testing for Flammable Gases

Two principal types of equipment are employed:

a.    Portable flammable gas detector (explosimeter).

b.    Hand held pumps with detector tubes.

Hydrocarbon concentrations are usually monitored with an explosimeter. Hand held pumps with detector tubes are used to identify particular gases (including hydrocarbons).

Any atmosphere being sampled must be approached as if it is flammable and/or toxic and due precautions must be taken. The possibility of oxygen enrichment and deficiency must be considered.

The detector must be safe for use in any potentially flammable atmosphere and be certified accordingly.

8.0       Portable Flammable Gas Detectors

The commonly used portable flammable gas detectors operate by measuring the temperature rise of an electrically heated filament when a sample of the gas/air mixture is burned at the surface of the filament. The gas concentration is usually indicated on a scale calibrated in percentages of the lower flammability limit (LFL). Certain types of flammable gas detector give audible and/or visible alarms at pre-set levels (often 20% of the LFL).

Caution: Flammable gas detectors can ignite a mixture of flammable gas and oxygen - enriched air, and will give false, low readings in an oxygen deficient atmosphere. Where oxygen enrichment or deficiency is possible, an oxygen test must be performed first, and normal oxygen levels established before flammable gas tests are attempted.

Portable flammable gas detectors require calibration with a standard gas/air mixture before use, as well as a check on the battery. The factors which may affect the accuracy of such gas detectors include:

a.    Instrument error due to calibration for a gas other than that to be sampled, or high or low oxygen concentration.

b.    Ambient temperature variations (particularly high temperature).

c.    Poisoning of the filament in the detector (e.g. by hydrogen sulphide). When such risks exist, the detector should be calibrated both before and immediately after use.

d.    Gases or vapors above the upper flammability limit.

e.    Rapid air movement (over diffusion head).

f.     Inadequate maintenance, faulty zero adjustment, weak batteries and poor sampling techniques.

Every movement of the needle on the detector is important, and not just the final resting position. The first movement shows that some kind of combustible vapor is present, but the final rest position of zero can occur when the gas concentration is above the upper flammability limit.

Special explosimeters must be used for certain other flammable gases (non hydrocarbons), particularly hydrogen and hydrogen sulphide. If the presence of hydrogen is suspected, specialist advice must be obtained.

9.0     Detector Tubes

Certain solvent vapors and non-hydrocarbon flammable gases (such as hydrogen sulphide) may be detected using explosimeters, but specific identification is carried out using detector tubes. These are transparent tubes containing chemically impregnated granules which change color in the presence of the flammable / toxic gas which the tube is designed to identify and measure. The correct volume of the atmosphere being tested must be drawn through the tube.

10.0     Testing for Oxygen Deficiency and Enrichment

Before any confined space is entered, tests for oxygen content must be made in addition to those for flammable and toxic gases.  Fresh air contains approximately 21% by volume of oxygen.

Locations where oxygen deficiency is likely include:

·        Spaces which have not been thoroughly ventilated.

·        Closed, empty tanks and vessels.

·        Spaces which have been purged with inert gas.

·        Spaces in which another gas has displaced the air.

Locations where oxygen enrichment is likely include:

·        Confined spaces in which oxy-acetylene or oxy-propane supplies have been used.

·        Areas near oxygen cylinder storage.

Portable oxygen meters are available which can be pre-set to give an alarm at high or low oxygen concentrations (typically at 22% and 20%).

12.0     Testing for Hydrogen Sulphide

Tests for hydrogen sulphide, which is denser than air, are conducted using detector tubes, chemically impregnated tape (for very low concentrations), or instruments which measure the change in electrical resistance as hydrogen sulphide is absorbed on a heated semi-conductor gas sensor. The semi-conductor detector is located within an `explosion proof' housing, with gas entering via a flame arrestor; this detector can be subject to errors caused by; calibration error, humidity, wind and rain

JUAN ABDEL-AZIZ

EH&SS Specialist