For full compliance with the OSHA, standard governing confined spaces, 29 CFR 1910.146, it is necessary to rely on the expertise of safety and health professionals, such as industrial hygienists.
Atmospheric Hazards: Are some of the most dangerous, yet they frequently go unnoticed. A hazardous atmosphere is best described as an atmosphere where employees are exposed to a risk of death or incapacitation, injury or illness from one or more of the causes listed below…
Oxygen Deficiency: Normal air contains oxygen concentration levels around 20.8% by volume. When and if an oxygen level falls below 19.5%, then that area is considered oxygen deficient. When the oxygen levels drop in any area, they are replaced by other gases, for example carbon dioxide, which can be very dangerous or even fatal when inhaled. Rust, corrosion, fermentation or other forms of oxidation that consume oxygen can cause areas to become oxygen deficient. The decomposition of materials utilizes oxygen from the air to fuel the break down of those materials resulting in oxidation.
The impact of oxygen deficiency can be gradual or abrupt, depending on the concentration of oxygen in the air and also the concentration of other gases within the areas atmosphere. When the oxygen in the atmosphere decreases, the following physiological symptoms occur…
Oxygen Enrichment: Enriched air happens when the concentration of oxygen rises above 23.5% by volume which is reaching into unstable conditions. Because the oxygen levels are so high, the likelihood of fire or explosion is significantly increased.
Combustible Gases: There must be three elements for combustion to occur: fuel, oxygen, and heat. The heat ignites the oxygen, which supports the combustion and the fuel is what stimulates the explosion and or fire. This is known as the fire triangle, but if you remove one of the elements, then combustion will not occur. The percentage of combustible gas in the air is vital. As the ratio of gas to fresh air changes, the sample passes through three ranges: lean, explosive, and rich. In a lean range there is not enough gas in the air to burn and or explode. On the other side, in a rich range there is too much gas and not enough air to properly burn and explode. That middle range we refer to as “explosive” is entirely self explanatory. This range is the perfect mix of gas and air for an explosion to occur. Caution must be observed because if there is a rich range and a dilution occurs and the air is mixed with the gas, then the area can easily fall into an explosive range.
Toxic Gases: Physiological effects of the following toxic gases are common to confined spaces and are approximations because the health of an individual will bring about different reactions if exposed.
Carbon Monoxide (CO): CO is a colorless and odorless gas caused by the combustion of fuels with an insufficient supply of air or in some cases where combustion is incomplete.
Hydrogen Sulfide (H2S): H2S is a colorless gas and smells like rotten eggs but odor cannot be used as a warning because after breathing only a small quantity of the gas the smell disappears quickly. It is highly flammable and explosive in high concentrations. It is found in sewers or sewage treatment facilities and in petrochemical operations. Abrupt poisoning may cause unconsciousness and respiratory arrest. In less sudden poisonings, people will feel nausea, stomach distress, eye irritation, belching, coughing, headache, and blistering of lips.
Sulfur Dioxide (SO2): SO2 is a pungent and irritating gas when combusted. Severe exposure is a result of loading and unloading tank cars, cylinder or lines either rupturing or leaking, and fumigation abroad ships.
Ammonia (NH3): NH3 is a strong irritant that can generate sudden death due to bronchial spasms. Small concentrations that do not irritate are passed through the respiratory system and metabolized, so they no longer act as ammonia. If you have ever taken a “whiff” of a household cleaning solution and it took your breath away, then you can understand how a severe industrial exposure could affect you. Ammonia can actually be explosive if a tank or refrigeration system is released into an open flame.
Hydrogen Cyanide or Hydrocyanic Acid (HCN): Interferes with the respiratory system of the body and is a very rapid poison that causes chemical asphyxia.
Benzene: A volatile liquid that is colorless, flammable and has a rather pleasant, aromatic odor. Chronic poisoning may occur after breathing a comparatively small amount over a period of time. There are signs which signal you when a poisoning has occurred, and they are: exhilaration, sleepiness, dizziness, vomiting, trembling, hallucinations, delirium and unconsciousness.
Toluene: A flammable colorless liquid which has a strong odor which warns it is in high concentration. Toluene produces effects like extreme fatigue, mental confusion, exhilaration, nausea, headache and dizziness.
Xylene: A solvent mixture that is similar to benzene in many chemical and physical properties.
| Substance | *Threshold Limit Value (PPM) | *Short Term Exposure Limit (PPM) | OSHA Permissible Exposure Limit(PPM) |
|---|---|---|---|
| Carbon Monoxide | 25 | -------- | 50 |
| Hydrogen Sulfide | 10 | 15 | -------- |
| Sulfur Dioxide | 2 | 5 | 5 |
| Ammonia | 25 | 35 | 50 |
| Hydrogen Cyanide | -------- | 4.7 | 10 |
| Benzene | 0.5** | 2.5 | 1 |
| Toluene | 50 | -------- | -------- |
| Xylene | 100 | 150 | 100 |
Physical Hazards: After the atmospheric hazards of a confined space have been contained and recognized, it’s important to then check for physical hazards around the work place. Hazards like grinding equipment, agitators, steam or steam fittings, mulching equipment, drive shafts, gears and other moving parts can cause serious injury, especially in confined spaces. They can burn, maim, or crush entrants in the space. Take special care in these dangerous situations and spaces. Pipe fittings and uneven or wet surfaces may also cause dangerous situations where you could slip, trip and or fall.
Engulfment Hazards: Engulfment hazards exist in areas where loose materials such as crushed stone, grains, flour, or sawdust are stored. These resources are often housed in silos or other containers and on occasion there are air pockets that form in the container, which can easily collapse on an employee under his/her body weight. When this happens either their airway is blocked or a compression of his/her upper body to the point where suffocation occurs.
Corrosive Hazards: Corrosive chemicals, such as acids, solvents, and cleaning solutions pose yet another confined space hazard. Contact to the skin, mucous membranes, or eyes can cause serious irritation or burns. Fumes given off by these materials or solutions can also irritate the respiratory system and can cause gastrointestinal pain.
Biological Hazards: Molds, Mildews, and spores frequently found in dark, damp spaces can irritate the respiratory system. Bacteria and viruses which are found in sewage treatment and other similar applications can also threaten the body with a variety of diseases. Bird and animal feces can cause serious health risks to humans.
Other Hazards: Poor visibility, inadequate lighting, and insecure footing can cause significant safety hazards in confined spaces. Also within confined space may be living rodents, snakes, spiders, or insects which may be dangerous and lethal. Also sudden changes in wind or weather can be a factor contributing to unexpected variations in the confined space environment.
References:
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Closing In On Confined Spaces: A Primer On Hazards and Equipment MSA: Mine Safety Appliances Company November, 2001.
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