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From the 2015 UPC Illustrated Training Manual
509.3.1 Appliance Draft Requirements.
This section provides an overall performance requirement for a natural draft vent system. The vent system must remove all the products of combustion from gas appliances from a building. The principle on which natural draft vents operate is simple. Reduced to fundamentals, heat is the power that operates a natural draft vent or chimney, as shown in Figure 509.3.1a. Combustion gases rise in the chimney or vent only because they are hotter and, therefore, lighter, than the surrounding air. The hotter the gases and the higher the vent, the more swiftly and powerfully the gases will rise. Conversely, the cooler the gases and the shorter the vent, the more sluggish the gases' movement will be. The flue gases in the vent must remain hot enough over the length of the vent to provide a strong draft. If cooled enough, the upward motion of the gases stops altogether and combustion gases can spill into the building through the relief opening of the appliance draft hood.
When the combustion products and dilution air rise in the vent, this volume must be replaced by air from outside the building. This replacement air can be supplied through normal air infiltration (through small openings in the building walls), through outdoor openings purposely installed in outside walls or by a mechanical air system. Thus, to ensure proper vent operation, the building's air tightness and other devices exhausting air from the building must be taken into account.
Fan-assisted combustion appliances cause some confusion because they are listed as Category I appliances, meaning that their vents operate by natural draft due to the heat of the vent gas. However, these appliances have a fan to assist the flow of the combustion product through the appliance. The fan is necessary because modern, higher-efficiency appliances have a higher pressure drop through their heat exchangers. The pressure provided by the induced draft blower is matched carefully to the resistance of the heat exchanger. Once the combustion products exit the appliance, the natural buoyancy takes over in the vent. If the vent is designed using the tables of Section 510.0, the pressure in the vent system will be negative.
Some furnaces are listed as Category I or III appliances, depending on the method used to vent the appliance. The fan in these furnaces is sized to result in negative vent pressure when connected to a properly sized vertical vent (Category I) or in a positive vent pressure when vented horizontally (Category III). Category III installation requires using venting materials recommended by the manufacturer's installation instructions.
Blockage of a natural draft vent may cause flue gases to spill into the building through the relief opening of the draft hood. Spillage can also be caused if the pressure in the vicinity of the appliance is much lower than the pressure outside the building (depressurization). Depressurization may be caused by mechanical exhausts, fireplaces, wind — anything that removes air from the building. Consequently, periodically verifying the performance of appliance venting systems is wise. Verification can be done readily with a natural draft system, described as follows:
Good air circulation in adequate amounts is also vital for good venting and effective appliance operation. Signs of improper operation include a yellow or wavering flame, discoloration around access doors, a pungent odor in the building, excessive humidity, condensation or mold, corrosion of the vent material and soot near the burner or vent area. If any of these conditions are observed, a qualified agency should be contacted to have the installation inspected.
Under extremely adverse conditions, carbon monoxide can be produced as a result of either improper venting of combustion products, insufficient fresh air to support the proper burning of gas, or improperly adjusted appliances. If symptoms of carbon monoxide poisoning are experienced — headache, yawning, ringing in ears, weariness, vomiting, heart fluttering or throbbing — fresh air is needed promptly. Open windows or go outdoors. Any gas appliance suspected of operating improperly should be shut off and immediately checked by a qualified agency.
From the 2015 UPC Illustrated Training Manual
603.0 Cross-Connection Control.
603.1 General. Cross-connection control shall be provided in accordance with the provisions of this chapter. No person shall install a water-operated equipment or mechanism, or use a water-treating chemical or substance, where it is found that such equipment, mechanism, chemical, or substance causes pollution or contamination of the domestic water supply. Such equipment or mechanism shall be permitted where equipped with an approved backflow prevention device or assembly.
The prevention of cross-connections is a primary responsibility of the plumber, maintenance or service worker. A thorough knowledge of backflow prevention and installation and testing of backflow prevention devices is needed to ensure the protection of the water system. IAPMO's Backflow Reference Manual contains comprehensive information on installation, testing, cross-connection control, repair, and inspections.
Cross-connection means any actual or potential connection or structural arrangement between a public or private potable water system and any other source or system through which it is possible to introduce into any part of the potable system any used water, industrial fluid, gas or substance other than the intended potable water with which the system is supplied. Bypass arrangements, jumper connections, removable sections, swivel or changeover devices and other temporary devices through which backflow can occur are considered to be potential unintended cross-connections.
There are two types of cross-connections – direct and indirect cross-connections. There are two types of backflow caused by these cross-connections – backsiphonage and backpressure backflow – and there are two types of backflow conditions – pollution (low hazard) or contamination (high hazard).
Polluted water may have an undesirable taste, color, or odor, but it is not considered unfit for human consumption and will not cause sickness. Contaminated water is water that is not safe for human consumption and will cause sickness or even death. Contaminated water is always considered to be nonpotable and requires a more absolute method or device to prevent backflow. It must be understood that a device or method that is suitable for only isolating potable water from a potential pollutant may be unacceptable as a means of protection against contamination. For example, a double check valve backflow assembly will be acceptable for a pollutant (low hazard) but not for a contaminant (high hazard).
For a cross-connection to occur, a link or channel between a polluted water source and pipes carrying potable water must exist. Two factors are essential for backflow to occur in a cross-connection. First, there must be a link between the two systems; this consists of either a physical connection or an arrangement or situation where backflow can occur. Second, an unbalanced force of liquid pressure must act toward the potable water supply.
In a direct cross-connection there must be a direct physical connection existing between the potable and nonpotable system. An increase in pressure must also exist on the downstream side of this connection causing a reversal of flow from the original intended direction of flow. Backflow occurs when the pressure within a polluted system exceeds the pressure in the potable water system. This is a backpressure cross-connection. A typical example of this type of cross-connection is the quickfill line for a boiler. The treated water in the boiler and connected piping represent the hazard, in this case a high hazard. This is because the pump circulating the fluid in the piping system could cause an increase of pressure above the quickfill line supply pressure and cause a backflow of treated water into the potable supply. Therefore, Section 603.5.10 requires a reduced pressure principle backflow prevention assembly where chemicals are introduced into the system (see Figure 603.1a).
The other type of cross-connection is an indirect crossconnection. There are two types of indirect cross-connections – under-rim or submerged connections, and over-rim connections. The under-rim or submerged cross-connection is where the water inlet comes into the bottom or side of a receptacle and is immersed in a polluted or contaminated substance (see D in Figure 603.1c). Without some form of protection just the filling of the lavatory to its rim could cause backflow into the potable water supply.
An over-rim connection is one where the water supply terminates above the flood level rim of a fixture but has a hose fitting or connection that creates a potential for an under-rim termination (see A, B and F in Figure 603.1c). In this instance, the over-rim supply line may not be continuously submerged unless a hose is permanently attached. Backflow may occur if the hose is left in the sink and something happens to cause a negative or lower pressure in the fixture supply, such as a break in the line or draining the system while leaving the fixture valve on. This will cause a siphon to occur drawing the possibly contaminated water into the potable water supply. The type of backflow that occurs in these instances is backsiphonage. See Figure 603.1cfor other examples of backsiphonage.
The control of backflow requires removal of one of the two essential factors that can cause the backflow; namely, the physical link or the cause of the negative or low pressure. Removal of the physical link or cross-connection, such as in Figure 603.1b is a positive means of preventing backflow and is the only true means of preventing bacterial contamination. This can also be accomplished with a backflow prevention device or an air gap as specified in the following sections. The appropriate selection, installation and testing of the devices are functions essential to the process of isolating pollutants and contaminants from the potable water system.
There are two basic areas where backflow protection is required. The first is the protection of the public or private water supply. The water purveyor may require all connections to the public water supply to have some form of protection. In some areas this may mean that every water service to a public, private or residential building may require a backflow prevention device to protect the system. This is called containment protection. The public water supply is contained and protected from contamination.
The other area of protection is inside or outside the building downstream of the containment protection. There may be connections to equipment or systems that could contaminate the building water supply. Backflow protection is required at this connection. This is called isolation protection. The contaminated fluid is isolated downstream of the connection to the building water supply. An atmospheric vacuum breaker on a urinal is a case of isolation protection.
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