Sewers fire water

When water suppression systems are provided, due concern should be made for the disposal of the released water. Of primary importance are the capacity and location of surface drainage systems. Fire water usage usually places greater demands on a facility gravity sewer system than rainfall or incidental petroleum spillage effects. 

In addition to a system for disposing of rain, fire, and wash-down water, many process units require special dedicated sewer systems (i.e., chemical and oily water sewers) for routine nonemergency drainage of process waste due to environmental, waste disposal, cross-contamination, or reactivity reasons. Chemical, process, or oily water sewers are usually not appropriate in capacity or purpose for use in drainage of large uncontrolled process spills, rain water, or fire water. 

Other utility systems. Other utility systems required in a refinery are electric power distribution, instrument air, drinking water, fire, water, sewers, waste collection, and so forth. Since these are difficult to estimate without detailed drawings, the cost is normally included in the offsite facilities. 

The presence of a trench/pipe system in Option B, used to remove rain accumulations, increases the risk that contaminated fire water might be inadvertently discharged into the sanitary sewer system. In order to reduce this risk, it is necessary to install a motorized valve in the drainage piping. This valve could be arranged to close automatically in the event of a fire through a signal from the fire alarm panel and manually as needed. It may also be desirable to use a valve which will automatically close in the event of loss of power. Alternatively, this valve could be normally closed and opened when needed. 

Contaminated fire water should never be routed to the sanitary sewer. Where a combined sewer system makes separate discharges impossible, it is critical that the valve be closed in the event of fire water discharge. Under no circumstances should the contaminated fire water be allowed to discharge to the local publicly owned treatment works (POTW). A trap tank or sump to separate any light layer may be appropriate, particularly where contaminants are not water-miscible. 

Fire water from hoses should be included in the storm water nmoff, if flooding would cause damage to installations and present a hazard during fire fighting operations. The storm-water main should be run to the battery limit and connected to the trunk sewer. 

Refinery and chemical plant sewers collect storm water, spent cooling water, condensate, varying amounts of spills and leaks and, under emergency conditions, fire water and blow-down. Sometimes separate storm sewers are used and an... 

Backup or flooding in a municipal sewer may inconvenience motorists and may cause some property damage. Around a refinery or chemical plant unit, backup can cause serious fires of spread fires that are confined to one area. Thus, in sizing a branch sewer or lateral, it is very important to consider the probable amount of fire water which may be used in the event of fire. 

On crude oil units the problem may be aggravated if the blowdown from the imit discharges into the branch sewer. The quantity of fire water will depend on the number of hoses and turret nozzles that would be drained to a given area. For branch sewers from units, the flow specified by various refiners range from 1,000 gpm to 2,500 gpm plus normal process water flows. Storm flows will depend on the geographical area in which the refinery is located. 

Fire water from hoses should be considered in the sizing of any sewer system, depending on the unit area location of any hazardous hydrocarbon and flammable chemical equipment. If fire water is to be included in the estimated maximum flow quantities, sizing should be based on (1) fire water plus total process waste waters or (2) storm water plus total process waste water — whichever is the greater. 

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. 

Hazardous areas subject to fire water from hoses should have sewer branches from each area sized accordingly. The amounts are not to be cumulative when estimating the size of sewer mains. One single 500 or 1,000 gpm allowance for the fire water flow quantity should be added to the sewer main flows — regardless of the number of hazardous areas within the plant site — starting at the upstream end of the sewer system under consideration. 

In the case of chemical spills due to process upsets, particularly fire and explosion, the chemical spillage on-site may be extensive and the water used on the fire can become contaminated with one or more process chemicals. Containment for fire water mnoff should be planned for all manufacturing plants at the design stage. Containment volume should also be provided on-site to ensure that no contaminated water leaves the site after a small or a major incident. Such water should not be flushed into a ditch, sewer, or drain or off the road since this would spread the chemical farther. The key feature of a well-designed chemical spill or contaminated water containment system is the ability to pump the spilled liquid into recovery containers for treatment. These large containers of contaminated liquid can then be treated by the conventional adsorption contacting systems as described in Section 15.3. 

Sewer boxes should be made of precast reinforced concrete pipe a minimum of 48 in (1,220 mm) in diameter. The system engineer establishes the need for sealed sewer boxes. Those containing clean storm or fire water do not require sealing, but toxic hydro-. carbon-bearing run-off requires a sealed sewer box that is vented to a safe location, as shown in Exhibit... 

The purpose of the facilities described in this chapter is to provide for safe handling of various drainage materials and emergency streams, so that they may be safely routed to the sewer, tankage, flare, or other appropriate destination. Drainage systems specified herein ensure that flammable or toxic materials may be disposed of without hazard of fire or injury when equipment is taken out of service. Also described are systems to handle process water drawoffs, cooling water, and other aqueous effluent streams which may be contaminated with hydrocarbons, and which could otherwise create hazardous conditions if they were discharged directly to the sewer. 

Underground and underwater Underground fuel/oil tanks and pipelines water, fire protection, gas and compressed underground air distribution schemes underground metallic sewers and culverts underground communication and power cables deep wells other buried tanks and tanks in... 

A terrorist release of weapons of mass destruction damage to chemical and industrial plants, sewer lines, and water distribution systems and secondary hazards such as fires will result in toxic environmental and public health hazards to the surviving population and response personnel, including exposure to hazardous chemicals, biological substances, radiological substances, and contaminated water supplies, crops, livestock, and food products. 

It is also a best practice to collect run-off water from the plant area and treat it in the site waste water plant before discharging it to the environment. Run-off water can come from rain, fire hydrant flushing, and equipment washing. As the water flows over the ground around the plant, it can become contaminated with organic chemicals that have leaked from the plant. Most plants are designed so that all the run-off is collected into local sewers or ditches that are routed to the site waste water treatment plant. 

Water was drained from the bottom of a gasoline tank into a sewer, and shortly thereafter a flash fire occurred in the sewer. The operator took special care to make sure that none of the gasoline entered the sewer. 

Full Running Sewers. Some trunk sewer systems rely on the sewer s running full to maintain a seal between operating areas. This is particularly true in the older sections of many plants. As the plants are modernized, many of the older units become obsolete and are taken out of service. If the spent cooling water and process water to these trunk sewers is thereby reduced, the sewer may flow only partially full. Under these conditions a fire in one section could be spread to other areas through the sewer. 

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