Physical Hazards in Confined Spaces
In addition to atmospheric hazards, a confined space must also be assessed for physical hazards. These hazards include those associated with hazardous energy releases, grinding equipment, dry particles that can engulf an entrant, communication problems, noise, temperature, and size of openings into the space.
Engulfment in loose materials is one of the leading causes of death from physical hazards in confined spaces. Engulfment and suffocation are hazards associated with storage bins, silos, and hoppers where grain, sand, gravel, or other loose material are stored, handled, or transferred. The behavior of such material is unpredictable, and entrapment and burial can occur in a matter of seconds.
In some cases, material being drawn from the bottom of storage bins can cause the surface to act like quicksand. When a storage bin is emptied from the bottom, the flow of material forms a funnel-shaped path over the outlet. The rate of material flow increases toward the center of the funnel. During a typical unloading operation, the flow rate can become so great that once a worker is drawn into the flow path, escape is virtually impossible.
A condition known as “bridging” can create additional hazardous situations. Bridging occurs when grain or other loose material clings to the sides of a container or vessel that is being emptied from below, allowing a hollow space to be created. The bridge of material over the space may collapse without warning, entrapping workers who are standing below or on top of the bridge and who are unaware that the surface is unstable.
Bridging can occur in storage bins, silos, and hoppers that contain ground grains, soybean meal and other meals, or other loose materials such as cement, limestone, coal, and sawdust. The diameter of the storage vessel and the moisture content of the stored materials are factors that contribute to bridging.
The nature of confined space work may make it difficult to separate the worker from hazardous forms of energy such as powered machinery, electrical energy, and hydraulic or pneumatic lines. Activation of electrical or mechanical equipment can cause injury to workers in a confined space. It is essential to de-energize and lock out all electrical circuits and physically disconnect mechanical equipment prior to any work in confined spaces.
The release of material through lines which are an integral part of the confined space pose a life-threatening hazard. All lines should be physically disconnected, blanked off, or a double block and bleed system should be used.
Falling objects can pose a hazard in confined spaces, particularly in spaces that have topside openings for entry through which tools and other objects may fall and strike a worker. Traffic hazards from forklifts and street traffic, even inattentive pedestrians, can pose a danger for entrants. Operational processes in close proximity to the space may create hazards or release toxic substances that migrate into the space.
Interior surfaces that are uneven, wet, or slick can cause falls in confined spaces. In addition, wet surfaces can provide a grounding path and increase the hazard of electrocution in areas where electrical equipment, circuits, and tools are used. Workers in some confined spaces need to be aware that objects may fall on them, particularly in spaces with topside openings and where tasks are being done overhead.
Grinding equipment, agitators, steam or steam fittings, mulching equipment, drive shafts, gears and other moving parts pose a danger if they are not locked or blocked out prior to entry.
Extremely hot or cold temperatures can make work inside a confined space hazardous. Heat stress increases fatigue and the inability to concentrate. Jobs requiring manual dexterity are more difficult in cold environments. Entrants working in spaces with great temperature variances should wear appropriate protective clothing. If a confined space has been steam cleaned, it should be allowed to cool thoroughly before any entry is made.
Noise within a confined space may be amplified because of the design and acoustic properties of the space. Excessive noise is not only harmful to a worker’s hearing, but can also affect communication, such as causing a warning to go unheard. This is especially true when hearing protection is being worn.
Biological hazards such as molds, mildews and spores frequently found in dark, damp spaces can irritate the respiratory system. Bacteria and viruses, found in sewage treatment, expose the entrant to a variety of illnesses. In addition, rodents, snakes, spiders and other insects, as well as bird and animal feces can present serious health hazards.
The presence of dust may pose dangers to entrants in the form of respiratory hazards. Dust also has the potential to cause combustion or an explosion and cause reduced visibility and slippery surfaces within the space. Other conditions, such as inadequate lighting and the presence of radioactive matter within the space must be evaluated before entry.
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