Document evNgrvQqZdmNzQe8bGgqoexz4

EXHAUST SYSTEMS, GENERAL O COMFORT VENTILATION of less importance, from the industrial hy giene standpoint, than the carbon monoxide released. For an 8-hour exposure, the permissible limit of carbon monoxide gas in air is 100 ppm, but a ventilating system should be de signed to keep a much lower level of carbon monoxide (CO). This value should not be over 250 ppm of CO for one hour's ex posure Exhaust gases as released from an en gine contain from 1 to over 10 per cent CO (1 per cent = 10,000 ppm) If the engine is operating at full rated horsepower, its ex haust gases will contain about 3 per cent CO. When idling, they may contain over 10 per cent Gasoline engines are built in many sizes, ranging from one to over 200 hp Lift trades commonly have a maximum delivery of 35 to 50 hp Since the engine normally discharges about one cfm of exhaust gases per operating horsepower, a lift truck when operating near its maximum rated horse power would release 0 03 times 50 or 1 5 cfm CO How much fresh air would be needed to dilute this CO output so the con centration would be below the threshold limit value would depend on many factors e Fully as important as the ventilation rate is the distribution of the incoming fresh air throughout the building A warehouse, for example, may have a central runway, with ware piled on each side in bays Dead-end alleys or aisles may lead into these bays and sometimes these constitute stagnant pockets The CO concentration may build up to excessive levels in an aisle when a truck is domg a stacking operation there, and still be negligible along the central run way Such a situation can best be solved by introducing the fresh air by a duct having discharge grilles in the pocketed regions, rather than along the central runway The latter generally receives adequate ventila tion from the building doors Improvement is sometimes made by ex tending the tailpipe of a warehouse track upward so it discharges vertically at a point above the operator's head This solution is effective, too, in a situation where a dump trade backs up to a pit hopper, at the bot tom of which there may be a conveyor Sometimes a man stands across the pit where the conveyor controls are located and he can get the full blast of the truck ex haust A vertical discharge pipe would pre vent this There are areas where it may not be practical or economical to ventilate for the prevention of objectionable concentrations if CO--such an area is frozen food storage rooms Electric trucks are recommended for these areas Finally, there is the garage which has fixed automobile repair stations Here the answer is a local exhaust system Threeinch flexible ducts are fitted over the tail pipes The flexible ducts join 4-in branches, which in turn are connected to a header located below floor level or overhead Ex haust requirements are shown in Table 28-0. The fan should be capable of exhausting the required air volume at 1V4 in. static pressure, water gauge For general garage ventilation, where cars are in motion or are idling outside of the repair stall, the following ventilation should be provided to dilute the carbon monoxide* Per running auto . 5,000 cfm Per running truck. 10,000 cfm (or more) Per horsepower for diesel........... 75 cfm Air sampling The ultimate effectiveness of any ventilation procedure for controlling CO should be verified by checking air samples for CO content Several instruments are available which use detector tubes in which a color change is produced if CO is present in the air sample. Other instruments axe available for continuous monitoring if this is thought to be necessary. Fog removal Hot water tanks are used in various in dustries and operations, such as foundries, veneer mills, plating, metal cleaning, and the like Sometimes the steam they release to the room leads to excessive moisture condensation, lowered viability, or discom fort Particularly is this true in winter weather, and at extensive vat operations See References at end of this chapter Dept of National Health and Welfare, Michigan Health Department, and Mdton Sheinbaum 28-44