SAFETY TALK
ATMOSPHERES IN CONFINED SPACES
A confined space is any area that:
- Has limited openings for entry and exit;
- May contain or produce toxic air contaminants;
- Has a high concentration of an inert gas;
- Is not intended for continuous occupancy; and
- May have an oxygen-deficient atmosphere.
- Electrical or mechanical hazards
- Has the potential for engulfment
All such spaces must be analyzed and tested before entry. Workers should also be trained to understand the hazards that may be found in these spaces.
A few of the potentially hazardous gases are:
Freon - This is a non-flammable liquid used primarily as a solvent for flushing a space or can be found as a gas in refrigeration systems. To prevent release, all refrigeration and transfer systems must be leak free. When working with Freon, there must be an alarm device in the area to warn of dangerous airborne concentrations. Since Freon is heavier than air, vapors will settle along the floor. Because of this, if the Freon alarm sounds or if you discover a leak, stand upright as you leave the area.
Carbon monoxide - This gas is usually produced by the exhaust of an engine or heater. It is colorless, odorless, tasteless, and deadly. If the air you breathe contains carbon monoxide, the gas interferes with your body's ability to utilize the oxygen that is in your lungs. In other words, you can still breath, but it does not do you any good. Unconsciousness, and often death, comes very quickly.
Hydrogen sulfide - This is a colorless, toxic, flammable and explosive gas with a rotten egg smell only at low concentrations. You may think that the smell alone would give you plenty of warning that the gas is present.
Beware--it doesn't!
After a whiff or two, in higher concentrations, the gas can desensitize your sense of smell, depending on the concentration, so you no longer detect the warning odor. Hydrogen sulfide is released during the decay of organic matter found in muds, sewage, etc., and is often prevalent during oil & gas drilling. It is heavier than air, so stay high if you suspect a problem and are trying to escape. Keep an eye out for blackened brass or copper pipes and fittings. Such indications could indicate that hydrogen sulfide gas is now present, or may have been in the past.
Carbon dioxide - Decaying animal or vegetable matter can create this gas, the gas may have been used to inert a space, or it may have leaked from a fire suppression system. The gas is odorless, colorless, and displaces the oxygen within the space, which can be fatal.
Ammonia -- This gas has good warning properties because it is extremely irritating to the eyes, nose, and moist skin. When exposure is gradual, most people are driven from the area before injury can occur. However, if the exposure is extensive or prolonged, severe irritation to the respiratory tract can result in respiratory arrest and death. If the odor of ammonia is strong, it is a sign that a leak exists, and must have attention before the space is entered.
Welding gases - Acetylene, oxygen, argon, and helium are all gases used in welding that might find their way into a confined space and threaten your life. These all have different properties and dangers but they most often enter a confined space due to a simple error, such as leaving an unused welding hose in the space. Never leave a welding gas hose in a confined space--even if it's turned off. It is too easy for someone to turn a wrong valve by mistake, and release gas that becomes a killer.
- Entry into confined spaces is potentially dangerous due to the possible presence of harmful atmosphere and/or condition,
- Any enclosed space that has one or more of the following critical conditions will be considered as a confined space:
- It has limited or restricted means of access or egress and not intended for continual use or occupation, (eg. Inspection pits, culvert, tanks, vessels & excavation >1.2m),
- Contain or the potential to have hazardous atmosphere -toxic, flammable, lack of oxygen- (eg. Vessels, drums, tanks & separators),
- Contains movable, sharp or hot parts, (eg. concrete mixers, hoppers & boilers).
- Gas tests are required before any confined space entry permit can be issued. The tests may include a flammable gas reading, oxygen content, and a test for toxic substances such as carbon monoxide, or hydrogen sulphide.
-
Vessels must be ventilated and have a
constant flow
of moving air before a
permit can be granted.Air blowers will be installed if
necessary. - Gas test limits for a normal vessel entry are: oxygen at 20.9% combustible gas at 0%, CO and H2S at 0 parts per million,
- If gas test results are out of the normal range, then special equipment such as respirators, protective clothing and forced air ventilation will be required, and it must be written on the entry permit.
- Gas tests are good for no more than 1 regular shift. Continuous gas testing may be required and will be provided by the Safety Department as necessary.
- Lighting inside vessels must be a maximum of 24 volts and must be a grounded system.
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