According to the U.S. Department of Labor, many workplaces contain spaces considered “confined” because their configurations hinder the activities of employees who must enter, work in and exit them. A confined space has limited or restricted means for entry or exit, and it is not designed for continuous employee occupancy. Confined spaces include but are not limited to underground vaults, tanks and storage bins, many used in wastewater pumping applications.
The Occupational Safety and Health Administration (OSHA) uses the term “permit-required confined space” to describe a confined space that has one or more of the following characteristics:
- Contains or has the potential to contain a hazardous atmosphere
- Contains a material that has the potential to engulf an entrant;
- Has walls that converge inward or floors that slope downward and taper into a smaller area that could trap or asphyxiate an entrant; or
- Contains any other recognized safety or health hazard (e.g., unguarded machinery, exposed live wires or heat stress).
The greatest danger facing the person entering a confined space is a lack of oxygen. Several breaths of an atmosphere holding less than 6% oxygen can disable in seconds and kill in minutes. Either the volume percent of oxygen can be too little (less than 19.5%) or other gases (e.g., carbon monoxide) in the confined space may interfere with the body’s uptake of an otherwise sufficient supply.
Oxygen deficiency also can debilitate sensors. Thus, a space with very low oxygen levels cannot be tested for combustible gases because standard instruments for this purpose require oxygen to function. (The sensor actually attempts to ignite a sample of the atmosphere and cannot do so when the fuel/oxygen ratio is too high.)
Not only is it dangerous to operate in a confined space, but it is also costly and time consuming for owners to maintain, according to Metropolitan Industries Service Manager Mike Schiazzano. He said that a permitted confined space requires a minimum three-man crew with the following safety gear in order to comply with very explicit codes: two multifunction gas monitors, tripod with safety retrieval line, safety harness, a fresh-air blower, a fresh-air tank with airline, respirator and escape pack. Training the crew to use all safety gear along with the retrieval equipment procedures is an added requirement.
“By eliminating the need to enter or work in a confined space, an operator can save time and money,” Schiazzano said.
Space Solutions
Above-grade applications greatly reduce the danger, cost and manpower issues associated with confined space applications. Installations typically consist of a small control and generator building installed next to a below-grade wet well containing pumps. The pumps are easily accessible and can be removed and installed without entering the well using a guide rail quick removal system.
Costs and labor to maintain such an installation are minimal. Given that it is above grade and anything below grade is accessible from above, typically one person can inspect and operate the entire station, reducing operating costs. Further reducing cost is the elimination of the equipment and safety apparatuses associated with confined space entry. Metropolitan Industries recently completed two such jobs in Merrillville, Ind., that eliminated previous confined space applications.
Broadfield Lift Station
Working with Robinson Eng. and contractor Hasse Construction, Metropolitan Industries supplied a triplex component lift station complete with a prefabricated building that houses the controls, valves and generator.
The triplex concrete lift station uses three 50-hp-rated for a total 1,442 gal per minute (gpm) at 89.2 ft of total dynamic head (TDH). One submersible level transducer—and four level switches for backup control—control on, off, override and alarm levels inside the basin. Access hatches, a pump removal lift-out system and guide rails allow easy access to pumps for maintenance without having to enter the 32-ft-deep basin.
All controls, valves and a backup generator were housed in a prefabricated above-grade building measuring 19 ft, 3 in. long x 13 ft, 6 in. wide x 11 ft tall. The building itself was divided into two sections—one side for the controls and valves and the other side dedicated to just the standby generator set.
On the control/valve side of the building, a triplex control panel with programmable logic controller and touchscreen operator interface controls the system. The discharge pipe and valve assembly are located above grade inside the building for easy access.
The generator side of the building houses a CAT 125-kW, three-phase natural gas generator complete with accessories. A 400-amp automatic transfer switch allows for transfer to the generator during power outages.
Other features of the building include an HVAC system for climate control, high-water alarm with dialer and battery backup, interior and exterior lighting and smoke detectors.
John Wood School Lift Station
The John Wood School Lift Station is another example of an above-grade application that eliminates confined space procedures. This application called for a duplex component lift station, again with a prefabricated control, valve and generator building.
The duplex concrete lift station uses two 40-hp submersible pumps, rated for a total 700 gpm at 113 ft TDH. One submersible level transducer and four level switches provide primary and backup level control inside the basin. Two lift-out hydraulic sealing flange assemblies allow pump removal for maintenance and repair without entering the sump.
As with the previous example, all controls, valves and a backup generator were housed in a prefabricated building of a similar size and layout. The building was again divided into two sections—one side for the variable speed controls and valves and the other side dedicated to just the natural gas CAT generator inside.
Other features of the building include an HVAC system for climate control, high-water alarm with dialer and battery backup, interior and exterior lighting and smoke detectors.
Reducing Hurdles
Above-grade applications eliminate the dangers and costs associated with confined space procedures. Towns and villages can save money by eliminating the special safety gear and reducing the personnel required by OSHA on a service call.
In addition, municipalities can save time by eliminating the requirement of obtaining a confined space permit that designates what is to be done, when and by whom. No longer will the loc
As demonstrated, a permitted confined space requires special handling, equipment and a fair amount of extra time and work if all the rules are followed. Above-grade applications at lift stations can reduce these hurdles.
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