Sewers manholes

FIGURE 6.6. H2S concentration in the headspace of a sewer manhole with and without addition of nitrate in an upstream located station. 

Will outdoor spills be protected from reaching storm water drains and sewer manholes ... 

OSHA cited a Texas construction company for workplace safety and health violations following the death of an employee who was working inside a sewer manhole. The employee was pumping grout into the sewer line and was overcome by hydrogen sulfide. The company faces 136,000 in proposed fines. 

Confined spaces include chambers, tanks (sealed and open-top), vessels, furnaces, ducts, sewers, manholes, pits, flues, excavations, boilers, reactors and ovens. 

Various detection devices will monitor the amount of flammable gases or vapors in an area. Portable gas detectors are used to detect the presence of combustible gas or vapor in basements, sewers, manholes, etc. Other devices will analyze the air samples brought into the device from various points. Gas and vapor testing equipment is valuable for preventing fires and explosions in petroleum and chemical plants and in industries where combustible vapors may be generated. 

A fire in a sewer manhole was caused by landfill gas migrating from the overlying refuse (Bailer, 1947)... 

Bailer L. C. (1947) Gas fire in sewer manhole traced to sanitary-fill operations. Engineering News-Record. December 25,1947. p 51. 

They would be used in complex entries, involving more than one person, hazards including moving machinery, electrical hazards, valve isolation, flooding etc. The permit would require time limits on entries, procedures, names of responsible persons etc. Most sewer/manhole entry work would not be done under a permit to work unless conditions as stated applied. However in factories for example, because of their complexity, every entry (tanks etc) should be carried out using a permit to work as the only satisfactory way of ensuring the safe system of work is complied with. 

A number of flume designs have been created specifically for use in partially fiUed circular conduits such as sewers. These are available in molded fiber glass and can be lowered through a manhole if required. As with all open-channel head-area meters, flumes must be sized to prevent submergence of the restriction. 

Storage areas for maintenance, janitorial, and other service organizations must be provided. Safety items such as fire extinguishers, firehose cabinets, safety hoops on permanent ladders, guard rads, shielding for acid pumps, clearance for electric panel boards, etc, are needed. Manholes and cleanouts for sewer pipes within the facility as well as in the landscape and parking areas should be provided. 

For low pressure pipelines that have ports open to the atmosphere, eg, sewers or closed effluent culverts, samplers are designed to sample through manholes. In a typical system, the Hquid is lifted through a suction line into the sampling chamber under vacuum. When filled, the vacuum shuts off, and the sample drains into a sample jar. A secondary float prevents any Hquid from reaching the vacuum pump. The suction line then drains by gravity back to the source. 

NFPA 328 Recommended Practice for the Control of Flammable and Combustible Liquids and Gases in Manholes, Sewers, and Similar Underground Structures, 1992 edition. National Fire Protection Association, Quincy, MA. 

Infiltration The seepage of groundwater into a sewer system, including service connections. Seepage frequently occurs through defective or cracked pipes, pipe joints, connections or manhole walls. 

The area below the stack and windbreaker is paved with concrete, surrounded by a 200 mm curb, and graded to a central drain point from which a drain line is routed to a manhole in a vented section of the oily water sewer. The water inlet should be sealed and the manhole should be located at least 15 m from the windbreaker. 

It is important to notice that H2S loses its characteristic smell at about 50 ppm, and, therefore, no direct possibility for its detection exists. The density of H2S is slightly higher than that of the atmosphere (relative density 34/29). Therefore, H2S has a tendency to accumulate in, for example, pumping stations and manholes. As it is typically not detected by its smell at those concentrations, where it is life threatening, instruments or alarm systems for its monitoring must generally be used when working in sewer systems. 

Special sewer structures like junctions, manholes, bends, weirs and drops may give rise to a turbulence that is increased compared with the hydraulic conditions that exist under normal sewer pipe flow. The turbulence introduced by these structures increases the air-water oxygen transfer, and the formulas in Table 4.7 are no longer valid. These special sewer structures typically have their own site-specific characteristics, and a simple empirical description of the reaeration at sewer drops and falls that includes only the most important parameters is needed. 

The effectiveness of nitrate addition to control sulfide has been investigated in a sewer network in the Lake Balaton catchment, Hungary (Jobbagy et al., 1994). Figure 6.6 shows the effect of nitrate addition on the H2S concentration in the headspace of a manhole located downstream of the station where nitrate was added. The importance of the anoxic removal of organic matter at the inlet... 

FIGURE 7.6. DO measurement in a manhole of a sewer. A bag (1) contains a waterproof box (2) with electrical equipment, data logger and batteries for a DO-meter (4). The float (5) is anchored by a steel rod (3). 

FIGURE 7.11. The investigated intercepting gravity sewer. Samples for OUR measurements were taken from the manholes in stations 1 and 4. Z length (m), D diameter (m), s slope (-). 

Process, chemical, or oily water sewer system branch and lateral lines should enter main lines through vapor-sealed and vented manholes. Branches and laterals in clean or storm water drainage systems may enter main lines without vapor seals if liquid-sealed catch basins are used on the inlets to these branches and laterals. 

Infiltration—Water that enters sewers through cracks and imperfect connections in sewers and manholes. 

In the manufecture of vinyl acetate, there is some unreacted acetic acid and other compounds that are discharged to the sewer. Your company has been cited as discharging more than the specified limit of several pollutants. It is not possible to measure the discharge directly because no flow measuring devices are in place, but you can take samples of liquid at different places in the sewer line, and measure the concentration of potassium chloride. At one manhole, the concentration is 0.105%. You introduce a solution of 400 g of KCI in IL at a steady rate of 1 L per minute over 5 hr at a manhole 500 ft downstream, and at 1200 ft downstream measure the average steady-state concentration of KCI as 0,281%. What is the flow rate of fluid in the sewer in kg/min ... 

A manhole over a sewer is tightly sealed to the road. The sewer flows through the bottom of the cavity formed by the manhole. Because of a leaky tank upstream, the wastewater contains 2 ppm of gasoline (model as 2,2,4-trimethylpentane). Trimethylpentane in air is explosive at concentrations between approximately 1 and 6% by volume (mole percent). Is there a possibility of an explosion Make reference to an idealized model you might use to calculate the trimethylpentane concentration in air, as well as the several possible complicating factors influencing the concentration of trimethylpentane in an actual situation. 

Use Underground sewer systems, manholes, industrial, and municipal. 

A somewhat specialized but highly effective form of cockroach control is the treatment of sewers and refuse chutes by the introduction of fogs or LJI.V sprays of synergized bi ores me thrill (0.15% BRM + 0.15% PBO) into manholes and access points (Chadwick and -Shaw, 1974 Chadwick et [Pg.255]

In many of the older cities, a large percentage of the sewer lines are well over the 40- to 50-year life normally anticipated. Recent studies indicate that in such areas, well over half of the total sewer line flow is from groundwater infiltration [1]. Other studies aimed at cost estimates for joint repair concluded that an excessive infiltration source (one or more joints) totalling 1 to 3gpm would typically occur every 50 to 100 ft between manholes. 

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