Confined space work is often considered to be one of the most dangerous types of work performed in power generation settings. Confined spaces may contain hazardous atmospheres, they can trap entrants, and they generally can increase the hazards associated with otherwise common tasks. When the risks are not recognized, workers all too often regard incidents as surprises, but the hazards of working in confined space can be predicted, monitored, and mitigated. These “accidents” are caused by unsafe conditions, unsafe acts, or both; all accidents are preventable.
Several common dangers found in confined spaces include the hazards of working with electrical equipment, engulfment, and releases from pipes containing fluids or gases.
Electrical. Electrical energy poses several threats to the health and safety of entrants going into confined spaces. For spaces with a potential for flammable atmospheres, both the equipment already in the space and the equipment used in the work performed may become ignition sources.
Arc flash, thermal burns, and other electrical hazards are particularly dangerous in a confined space because it may be difficult for the worker to avoid accidental contact or proximity. In most settings, policy dictates that such equipment simply be de-energized and lockout/tagout procedures put into effect. (For more information on the hazards of arc flash, see “Arc Flash Protection Should Be Job No. 1” in the February 2007 issue, or in POWER’ s online archives at http://www.powermag.com.) However, this is not always possible in a power generation environment. Instead, complex operational controls and tagging systems must be used to ensure proper safety (Figures 1 and 2).
|1. Restricted access. When dealing with confined spaces in power generation settings, operational controls and tagging systems must be used to protect the safety of workers. Courtesy: New Standard Institute Inc.|
|2. On alert. Confined space work at power plants requires the identification and removal of unsafe conditions, if possible; controlling access where conditions are inherently dangerous; and training entrants to prevent unsafe acts. Courtesy: New Standard Institute Inc.|
Engulfment. Many materials have the potential to engulf an entrant. When small solids are in motion, they begin to act like a liquid. Coal, sand, dirt, and other materials flow, following the shape of their container. The presence of materials with a combination of fluid and semi-rigid properties makes storage areas potentially hazardous. This is an especially important concern for coal-fired plants, where employees must walk across loose coal. A parallel hazard is bridging. When an auger operates, material flows out of the bottom of the storage area. Material at the top may not flow down evenly, forming a temporary bridge out of the material. Walking over the surface of bridged material can lead to immediate engulfment.
Pipes Containing Fluids or Gases. Pipes that carry liquids or gases also present several potential hazards. The condition of a pipe may be hazardous, as a leak could quickly create a dangerous situation. Valves, piping, and infrastructure in confined spaces may be hard to access and are inspected infrequently, so it is important to consider that the risk posed by leaks may be unknown.
Materials being transported in lines and piping, such as steam or coolant, may be at extreme temperatures. Even without a release, such pipes are potentially hazardous if entrants must work in close proximity, as this scenario increases the likelihood of unintentional contact. Gases being vented or brought to a process can quickly create a hazardous atmosphere. Even without obvious damage to lines, leakage usually occurs in most piping systems.
Otherwise nonhazardous fluids, such as water, may not be immediately threatening, but the introduction of any fluid to a confined space creates potential hazards. Fluid may conceal trip/fall hazards, come into contact with energized equipment, or may fill the space. Entrance into lines themselves is always potentially dangerous, and dead or decaying matter in those lines can cause a buildup of hazardous gasses in short amounts of time. Lines used to transport saltwater are particularly vulnerable to such organic matter, even if filters and other measures are taken to clean the incoming supply. Valves normally under pressure from liquids in a line may not seal as well as expected when the lines are drained, so air quality testing is incredibly important in these areas.
Spaces such as large tanks present the possibility of a stratified gaseous atmosphere. Gases have different densities and can rise or sink relative to each other. Gases like carbon dioxide tend to pool, while gases like methane and acetylene rise. Depending on the temperature and source of the gas, or whether the atmosphere inside the space is disturbed, these hazards may be found anywhere in a confined space. When left for some time, the atmosphere in confined spaces will tend to separate out. The air must be tested at small intervals in a potentially stratified atmosphere. Any suspected areas of reduced ventilation, such as behind a baffle or an internal barrier, should be tested as well. Always use a remote probe or sampling tube, and allow workers to advance into the space only as far as the atmosphere has been tested.
Successfully Evaluate Potential Risks
The situations mentioned above are just a few of the potentially hazardous conditions that warrant a stringent evaluation procedure when an employee will be working in a confined space. This evaluation should also include measuring the size of the space as well as access and egress availability. Oxygen, carbon monoxide, hydrogen sulfide concentrations, and the percentage of the lower explosive limit (LEL) in the confined space must be measured and analyzed. The atmosphere within the confined space should be measured in terms of its LEL; typical permissible exposure level (PEL) and time-weighted average exposure (TWA) for different gases are illustrated in Figure 3.
|3. Understanding the risks. Before a worker enters a confined space at a power generation facility, the plant safety officer should measure and analyze gases present to determine if the space has an explosive atmosphere or is otherwise a danger to human occupants. Courtesy: New Standard Institute Inc.|
Even the slightest potential for a change in air quality or hazardous atmosphere is cause for concern. A space that has walls that converge inward or floors that slope downward and taper could trap or asphyxiate an entrant. Area inspections must identify all of these potential conditions so that efforts can be made to mitigate or control any and all hazards before work begins. It should be considered likely that the space will require a permit entry program, though efforts to control the condition will make entry far safer.
As important as what is evaluated is who does the evaluation. Make sure the group is properly trained and qualified to perform evaluations. If a contractor has his or her own designated safety personnel performing evaluations, make sure they are qualified as well as audited. Many power plants are stepping up their safety programs and requiring all outside contractors to comply with internal programs and use certified equipment. The fact of the matter is that people may cut corners to save time and money; however, there is no acceptable compromise when it comes to safety. Audits should be frequent and unscheduled, and each work site should have an internal person assigned to that task.
Emergency communications should be well defined and centralized. A phone number or radio frequency needs to be on every document and work order so no one has to look far in the event of an emergency. Attendants must be in continuous communication with workers. Special attention will be required if the space or work performed will be creating excessive noise and workers must wear hearing protection.
Layout of the workspace can be critical as well. If workers are not visible from outside the confined space, alternate means must be employed. Radios, video monitors, or other methods should be considered. Some systems of communication, such as tugging on a safety line or rapping on the barrier of a space, are prone to error or misinterpretation and should be considered a backup method that is only suitable for use in an emergency.
Customizing Safety Programs for Power Plants
Confined space work requires the identification and removal of unsafe conditions, controlling access where conditions are inherently dangerous, and training entrants to prevent unsafe acts. This can be an especially difficult task for power generation facilities. Besides the usual confined spaces found in many industrial settings, power plants have additional challenges, including high-voltage hazards, tunnels, tanks, coolant lines, and dozens of other safety threats. The U.S. Occupational Safety & Health Administration’s 1910.146 standard sets out the requirements upon which safety specialists and operational managers should base safety programs for their individual plants’ operations.
—Contributed by Michael Konopka (firstname.lastname@example.org), product development manager at the New Standard Institute Inc. This article is adapted from the New Standard Institute’s confined spaces computer-based training.