Combustible Dust Atmospheres
Finely powdered dust from combustible materials such as wood, metal, or grain can be fuel for powerful explosions.
Carbon Monoxide
Dust clouds can develop as result of handling dusty materials or when solid materials are reduced to smaller particles from processes such as grinding, drilling, or crushing.
Airborne combustible dust at an explosive concentration would obscure vision at a distance of five feet (1.52 meters) or less. A direct reading instrument may be used to measure actual dust concentrations.
Toxic Atmospheres
Substances regarded as toxic in a confined space can cover the entire spectrum of gases, vapors, and finely-divided airborne dust in an industry. Toxic gases may be present in a confined space because:
- toxic substances are used as part of the production process, (for example, in producing polyvinyl chloride, hydrogen chloride is used as will as vinyl chloride monomer, which is carcinogenic).
- the biological and chemical "breakdown" of the product being stored in a tank, or
- maintenance activities (welding) being performed in the confined space.
Four common types of toxic gases encountered in confined spaces are:
- Hydrogen Sulfide (H2S) - or "sewer gas," is a colorless gas with the odor of rotten eggs. Excessive exposure has been linked to many confined space deaths. Hydrogen sulfide causes a loss of our sense of smell, causing people to mistakenly think that the gas has left the space. Hydrogen sulfide inhibits the exchange of oxygen on the cellular level and causes asphyxiation.
- Carbon monoxide (CO) - is an odorless, colorless gas that is formed by burning carbon based fuels (gas, wood). Carbon monoxide inhibits the body's ability to transport oxygen to all parts of the body.
- Methane (CH4) - is a natural gas produced from the decay of organic matter. It is a flammable, explosive, colorless, and odorless gas. It can displace oxygen to the point of oxygen deficiency in a confined space, causing dizziness, unconsciousness, and asphyxiation.
- Solvents - many solvents, such as kerosene, gasoline, paint strippers, degreasers, etc. are not only flammable, but if inhaled at high concentrations can cause central nervous system (CNS) effects. CNS effect can include dizziness, drowsiness, lack of concentration, confusion, headaches, coma and death. (Source: University of South Carolina)
Remember, atmospheric changes may occur due to the work procedure, the product stored, or a nearby gas line leak. The atmosphere may be safe upon entry, but can change very quickly.
- The work performed within the confined space (such as welding, degreasing, painting, or sanding) may produce toxic atmospheres.
- Toxic gases and vapors from adjacent areas can migrate to and collect in the confined space.
- Vapors may be released from the sludges on the bottom or scales on walls of emptied confined spaces, such as storage tanks, that previously contained flammable or toxic chemicals. Vapor release may be accelerated by wall scraping and sludge removal from confined spaces.
Confined spaces prevent toxic substances from escaping, diluting, or readily dissipating. Instead, substances can become trapped and a buildup occurs, whereby the concentrations of toxic substances reach dangerous levels.
The atmosphere inside a confined space can change rapidly and unexpectedly. Also, any ignition source (such as sparks from grinding or welding equipment, static electricity, or unapproved electrical equipment that is not non-sparking or even smoking) can initiate an explosion.
Knowledge Check Choose the best answer for the question.
4-6. Which of the following gases inhibits the body's ability to transport oxygen to all parts of the body.
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