Roof vents

Johnson, W. B. et al., 1975, Gas Tracer Study of Roof-Vent Effluent Diffusion at Millstone Nuclear Power Station, Atomic Industrial Forum AIF/NESP 0076. 

Virtually no mnning cost Self-regulation (flow rate increases with heat load) Low maintenance cost Provides daylight when open (roof vent) Psychological appeal of clear sky (roof vent) Easy installation... 

Fire Paper 7, Investigations into the flow of hot gases in roof venting, HMSO (now available from Colt International Ltd)... 

In the course of the survey, in addition to what you actually see, you should pay attention to the unexpected. A container, for example, properly processed, properly sited, and in all respects satisfactory, could unexpectedly rupture and spill its contents. Or, a toxic effluent extracted to a roof vent through an otherwise effective ventilation system (as we have seen with the tale of Mrs. Madison) could be pulled back into circulation through an improperly located air intake. One of the keys to the survey, in fact, is alert awareness. 

The geometry used for this example was a half-scale hallway. The dimensions were 114 inches (2.9 m) by 29 inches (0.74 m) by 48 inches (1.22 m). Figure 1 shows a schematic of the hallway. The hydrogen escaped from the floor at one end of the hallway (left hand side of figure). A roof vent and lower door vent existed at the other end of the... 

Figure 4 shows a comparison of the surfaces of constant 3% concentration for both helium and hydrogen. Both gases rise from the floor, travel across the ceiling, and leave through the roof vent. The gas leaving the roof vent causes a drop in pressure, which draws air in the lower door vent. The general circulation in the hallway can be seen in Figure 1. All of the gases inside and above the surface of constant 3% concentration contain more than 3% helium or hydrogen. Those below the surface contain less than 3% concentration.

Bottom firing (i.e., burners below the loads) delivers heat to the usually cooler hearth, making up for hearth losses that otherwise would be taken from the loads or from the gas blanket. (See fig. 7.3.) Bottom firing is sometimes used with roof vents, but roof flues can be undesirable because at low-firing rates, the gases may short-circuit direct to the roof flues (giving poor temperature uniformity and poor fuel economy). Roof vents also can cause negative or low furnace pressure therefore, oversize vents should be avoided, and furnace pressure should be controlled with a stack closure. Tall furnaces are especially susceptible to this problem. 

The second field test assessed PCO to treat paint solvent vapors. Painting operations for military and civilian vehicles are conducted in ventilated enclosures called paint booths. Filters in the exhaust ducts trap paint droplets from the paint overspray while the VOC-laden air is typically exhausted through roof vents. The vent emissions can contain several hundred parts per million (ppm) of the paint solvents, which continue to evaporate from the vehicle after painting is complete. Most types of paint generally contain significant amounts of VOCs such as toluene, a suspected carcinogen, as well as other hazardous solvents such as methyl efliyl ketone, methyl isobutyl ketone, hexanes, xylenes, n-butyl acetate, and other components in lesser amounts. 

One problem found across many industries and processes is the use of single-story facilities. As noted earlier, heat and smoke can move rapidly under the roof of a horizontal building. There are some techniques that can help confine fires in industrial plants. Ventilation is an important method. Roof vents allow hot gases to escape and do have some effect on confinement. 

The area formed by combustibles in a manufacturing facility is 35 X 40 ft. There are curtain boards extending 12 ft from the ceiling that end 15 ft above the floor. What area of roof venting is needed between curtain boards... 

Cross vents between the 105and 109-N Buildings 6tnd the roof vents cure blown open. 

Thirteen six-foot diameter roof vents from Zone I to the atmosphere are provided for the venting of steam In the event of a pipe rupture. Seven of these vents are located at the east end and... 

Inlet and outlet ducts close automatically when pressure exceeds limit. Eadiation detector haust line. Excessive air contamination will sound alarm permitting manual closing of roof vents from 10 -H control room. 

Normally air discharged through roof vents to atmosphere. Air can be combined with Zone I air from 105 Building, filtered and sent to stack. 

Ore concentrate storage Return sinter transfer Sinter sizes and storage Sinter product dump area Blast furnace roof vents Blast furnace upset Lead casting roof ducts Zinc fuming furnace area... 

These documents also provide guidance on internal and external mechanical inspections to be undertaken by a trained and competent tank inspector. All inspections and routine checks should be documented. Evaluation should include fixed roof venting, floating roof drainage and general... 

Provide information on fixed fire protection installations (eg roof vents, sprinklers, drenchers, fire shutters), with technical detail of their operation ... 

FIGURE 4.81 Curtain boards and roof vents. (From Fire Protection Handbook, 14th ed., G. P. McKinnon, ed., NFPA, Quincy, Mass., 1976.)... 

Figure 8.22 The use of wall and roof vents together, give good natural ventilation...

The first skill that a new homeowner should acquire is toilet repair. 1 had my first lesson on this vital skill in 1969. We had just moved into our first house in south Chicago when 1 discovered our toilet wouldn t flush. An experienced co-worker at the American Oil Refinery in Whiting, Indiana (now BP), suggested that 1 check the roof vent (see Fig. 1.2). 

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