Sewers catch basins

In addition, it is recommended that precautions similar to those which will be suggested for process sewers be taken to protect the separate storm sewers. In one plant, an explosion caused by an inflow of oily water resulted in considerable damage to a separate storm sewer. An oily-water catch basin had been mistakenly connected to this sewer. The source of ignition, while unknown, may have been welding near a storm sewer catch basin. 

An adequate drainage system should be provided for all locations where a large amount of hydrocarbon liquids has the possibility of release and may accumulate within the terms of the risk analysis frequency levels. Normal practice is to ensure adequate drainage capability exists at all pumps, tanks, vessels, columns, etc., supplemented by area surface runoff or general area catch basins. Sewer systems are normally gravity flow for either sanitary requirements or oily surface water disposal. Where insufficient elevation is available for the main header, lift stations are installed with a forced pressure outlet header to a disposal or treatment system. 

Common practice and a general guide is to prevent combustible vapors from transmitting from one process area to another process area, generally 15.2 meters (50 ft.) or more away. Usually unsealed receptacles, such as drain funnels, tundishes, drain boxes, are routed to the nearest local sealed catch basin and then into the oily water sewer main. The unsealed receptacles are only allowed in the same process area equipment where if vapors where released from an adjacent unsealed receptacle it would be "immaterial" due to the proximity to where the liquid is being drained and would normally emit vapors. 

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. 

CO = CLEAN OUT RL = ROOF LEADER SB = SEWER BOX CB = CATCH BASIN MH = MANHOLE DH = DRAIN HUB FV = FLAP VALVE -0= INVERT... 

Flap Valve. Storage areas which are curbed or diked should be provided with sufficient catch basins to accommodate the surface drainage. Sewer... 

Paved areas and unpaved areas outside should have a sewer box or catch basin for each surface... 

The divided areas should be provided with sewer boxes or catch basins. The separate sewer systems are now to be connected to the properly classified sewers. Sewer box or catch basin outlet connections may be at the bottom or side depending upon the sewer invert limits (see Figure 8-3). The term invert refers to the elevation at the bottom inside surface of the sewer pipe. 

The complete segregation of all sewer systems at this point will represent nothing more than a one-line dis am layout for each system. Catch basins and manholes should now be added to the layouts. 

Catch basins (see Figure 8-5) should be used as a junction for changes of direction of sewer branch lines. The location of branch sewer junctions may so coincide that a catch basin may be substituted for a sewer box, which would normally be provided for surface drainage. A catch basin should... 

Seals should be provided on all inlets of sewer branches and sewer mains connecting to a catch basin or manhole (see Figures 8-5 and 8-6). A seal should consist of an elbow or a tee with outlet extending downward to provide for a minimum 6-inch seal. Some plants use a special combination seal and cleanout fitting designed to be inserted into the wall of the catch basin or manhole when the concrete is poured. 

Areas considered hazardous because of accumulations of flammable gases in the sewer mains should have sealed or gasketed catch basin and manhole covers to prevent escape or leakage of gases from sewer lines. 

It is usually advisable to blind or block an unused branch or lateral where it enters an active sewer. When welding is in progress near open catch basins, the usual procedure is to seal the catch-basin lid with sandbags or place a tarpaulin with a cover of sand over the lid. Similar precautions should be taken near floor drains or other open drains that may be discharging flammable vapors. 

Floor drains inside buildings should only be used to handle water. A sewer box or catch basin should be used where process waste spille e may occur inside a building. 

A sewer branch or sub-branch should be run in one plane from a drain hub to a catch basin and from a catch basin to a manhole to prevent clogging of the sewer line and for easier rodding and cleaning. Whenever possible, aU branch connections to sewer systems should be made at catch basins or manholes. 

Manholes with open tops covered with grating may be used to collect surface drainage as explained for catch basins. The grating cover for sealed manholes requiring vent connections should be filled with concrete and sealed or bolted down tightly to prevent the escape of sewer gases. 

Invert. The invert of the sewer inlet and outlet at a catch basin or manhole should be at the same elevation when both inlet and outlet sewer mains... 

Unit areas containing fire water to be collected by two catch basins should have a branch sewer assumed to receive 500 gpm. Unit areas containing fire water collected by as many as four catch basins should be assumed to received 1,000 gpm. 

Variations of pipe fittings, catch basins, sewer boxes, trenches, sumps, and lift stations are only a sample of what a plant layout designer encounters in the development of an underground piping system. Available vendor data for fittings, catch basins, and sewer boxes must be used as a reference. Typical cast iron fittings are shown in Exhibit 13-39. The list of labels for these... 

Drainage—Surface drainage and safe removal of spilled or accumulated liquids is adequately provided and arranged to prevent exposure to the hazard to the process system or critical facihty support systems. Liquids should be immediately removed from an area through surface runoff, drains, area catch basins, sumps, sewers, dikes, curbing, or remote impounding. 

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