The Dangers Of Confined Spaces

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The Dangers Of Confined Spaces

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A confined space meets any one of the following characteristics:

  • Large enough for a worker to enter
  • Not designed for continuous worker occupancy
  • Limited or restricted means of entry and exit

Always be alert when entering any confined space. Unfortunately, occupational injuries involving confined spaces rose 15% in 2017 and continue to be too common. A history of entering a space without incident is not a good indicator that the space is safe; it is not uncommon for workers to die in spaces that have been entered before without incident. More than 60% of confined-space fatalities are would-be rescuers, so a well-designed emergency plan is a must.

You can minimize the risk to workers in confined spaces with careful planning and preparation, thorough training and proper procedures. Follow these recommendations for safety in confined spaces.

Identify confined spaces

The most obvious confined-space areas for drain and sewer cleaners are sewer manholes and septic tanks; however, any area which meets the criteria above qualifies as a confined space.

Other examples include, but are not limited to, pipelines, culverts, underground utility vaults, lift stations, storage tanks, tunnels and pits more than 4 feet deep. Pits can include sump pits, valve pits or vaults (e.g., wastewater treatment plants, municipal water systems), electrical pits/vaults, steam pits/vaults, vehicle service/garage pits, elevator pits, dock leveler pits, industrial chemical waste pits and many more. It's important to remember that every space is unique, and each requires careful evaluation.

According to OSHA, sewer entry differs in three ways from other confined-space entries:

  1. Because it is part of a continuous system, there is rarely any way to completely isolate the space to be entered.
  2. Because it isn’t possible to completely isolate the space, the atmosphere is unpredictable and may suddenly become lethally hazardous (toxic, flammable or explosive) from causes beyond your control.
  3. Material flowing through the sewer system can engulf workers.

Know the risks

The key to minimizing the potential hazards in confined-space entry is to know and prepare for the risks.

Atmospheric hazards

There is a lack of natural air movement in a confined space. This can cause the atmosphere to be oxygen-deficient, oxygen-enriched, flammable or even toxic. All are dangerous. Always ventilate a confined space with normal air. To avoid an oxygen-enriched atmosphere, never use pure oxygen to ventilate a confined space.

Confined spaces should not be entered without proper safety equipment and an approved self-contained breathing apparatus. All applicable OSHA guidelines must also be followed.

Toxic atmospheres contain liquids, vapors, dusts or gases and should always be considered hazardous. Confined spaces involving human waste are especially dangerous because when human waste putrefies, dangerous gases are generated. There are four major gases that can result from putrefying waste. 

Four major gases that can be found in sewers

1. Hydrogen sulfide (H2S) — Hydrogen sulfide is a highly toxic and flammable gas. It’s often produced from the microbial breakdown of organic matter in the absence of oxygen gas, such as in swamps and sewers. Since hydrogen sulfide is heavier than air, it accumulates at the bottom of poorly ventilated areas. 

Hydrogen sulfide smells very pungent at first, like rotten eggs, but it quickly deadens the sense of smell. Victims may be unaware of its presence until it’s too late. Exposure to lower concentrations can result in eye irritation, a sore throat and cough, nausea, shortness of breath, and fluid in the lungs. Short-term, high-level exposure can cause you to collapse immediately, with loss of breathing and a high probability of death. Under the right conditions, hydrogen sulfide will oxidize to sulfuric acid, which is highly corrosive. If you’ve ever seen sewer pipe eroded at the top (crown), chances are sulfuric acid did the job.

2. Methane (CH4) — Methane is the main constituent of natural gas and can be produced by the decomposition of organic matter. It’s lighter than air and is likely to be found at the top of a confined space. Methane is colorless and odorless. Methane is nontoxic, but it’s not harmless. Not only is it extremely flammable, but it’s also an asphyxiant at an oxygen concentration below 16%.

3. Ammonia (NH3) — Ammonia is a colorless gas with a characteristic pungent smell. Ammonia is both caustic and hazardous in its concentrated form. Urine is high in ammonia, and it’s also a byproduct of the decomposition of organic matter. Exposure to high concentrations of ammonia in air causes immediate burning of the nose, throat and respiratory tract. This can result in respiratory distress or failure. Ammonia’s odor provides an early warning signal, but ammonia also causes olfactory fatigue which reduces awareness of its presence.

4. Carbon dioxide (CO2) — Carbon dioxide is a colorless gas that is odorless at normally encountered concentrations. At high concentrations it has a sharp acidic odor. In concentrations up to 1% (10,000 ppm), carbon dioxide will make some people feel drowsy and give the lungs a stuffy feeling. Concentrations of 7% to 10% (70,000 to 100,000 ppm) may cause suffocation, even in the presence of sufficient oxygen, manifesting as dizziness, headache, visual and hearing dysfunction, and unconsciousness within a few minutes to an hour.

Physical hazards

Physical hazards are hazards that cause the body to become physically stressed. Unlike atmospheric hazards, physical hazards can be determined through your senses (touch, sight, etc.). Physical hazards can include:

  • Entrapment: Inwardly converging walls or floors that slope downward pose a hazard to the worker.
  • Engulfment: The surrounding or burial of the worker in a liquid or solid material, such as sand or grain, which can suffocate a worker. Engulfment could happen through accidental dumping of a product on a worker, or through a worker walking on unstable material such as settled grain.
  • Slips, trips and falls: A confined space may have a hatchway that is difficult to squeeze through, and ladders for ascending or descending. There is a greater risk of falling while getting into the space as well as while inside. In addition, the flooring of tanks or other wet environments or the rungs of a ladder may be very slippery.
  • Falling objects: There may be danger of being struck by falling objects such as tools or equipment, particularly if access ports of workstations are located above workers.
  • Moving parts of equipment or machinery: Moving equipment or parts and energized or pressurized systems can be dangerous. Examples include shafts, couplings, gears, belts, conveyors, mixers, rotors and compressing devices.
  • Electrical shock: All electrical sources that pose a hazard to workers inside the space must be locked out following the written lockout procedure for the confined space.
  • Substances entering through piping: Piping adjacent to a confined space could contain liquids or gases or other harmful substances. Substances must be prevented from entering the confined space through piping. This is done by “isolating” the piping from the confined space.
  • Poor visibility: Emergency lighting such as flashlights or battery-operated area units must be provided where necessary, so that workers can locate exits and escape.
  • Thermal hazards and temperature extremes: A thermal hazard is a dangerous condition caused by excessive heat or cold. Special precautions are needed before workers enter equipment such as boilers, reaction vessels and low-temperature systems. Employees engaged in continuous heavy work while wearing PPE in warm surroundings are particularly susceptible to thermal hazards. Heat stress may lead to heat exhaustion, heat cramps, heat stroke, loss of consciousness or death.
  • Noise: Sounds generated by tools and heavy machinery can be magnified and reverberated within confined spaces. Noise may impede verbal communication between workers. Over time, excessive noise may also impair a worker’s hearing.

Psychological hazards

Psychological hazards include fatigue, claustrophobia, fear of heights, fear of darkness and more. Even having a mild level of claustrophobia or fear of heights can cause problems. There’s not much you can do to resolve psychological hazards except to not put affected workers into spaces that cause them problems.


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