Document 7790aJjewZnY65M9rBV8vkmj

Automotive crus Machine Shop Industries Checking Performance oi Process Exhaust Systems By W. G. HAZARD DirM Industrial Hygiene, Owens-Illinois Glass Co., Toledo, Ohio Checking Performance of Process Exhaust Systems 5 FORM 1--Safety Engineer's Inspection Report Condition of hood and branch (Battered? removed? plugged? repair?) Static press. (inches water) Checked Some twro-and-a-half years ago the Health Maintenance Committee of this section un dertook to develop a data sheet on the main tenance of local exhaust systems. The jcb is now about completed, with the help of the whole committee, and your program chair man has asked that we give you a preview of it. Purpose The purpose of the data sheet is some what different from that of most articles that have appeared on exhaust systems. What's made this possible has been the timely appearance m the last few years of outstanding books on the technical design of exhaust systems. Among these publications are: 1. Manual of Industrial Ventilation (1952) American Conference of Governmental Industrial Hygienists 2. Industrial Health Engineering (1947) A. D. Brandt 3. Industrial Hygiene and Toxicology (1948) Frank A_ Patty, Ed. (Chapter 10-- Ventilation, by \V. X. Witheridge) 4. Exhaust Hoods (1952) I. M. DallaValle 5. Accident Prevention Manual (1951) National Safety Council (Chapter 21 --Industrial Health Engineering) 6. Ventilation W. C. L. Hemeon 7. Industrial Dusts (2d edition) Phillip Drinker and T. F. Hatch To be published 8. Design data published by numerous man ufacturers. such as American Blower Corporation, American Air Filter Com pany, Buffalo Forge Company, Westinghouse, and others. The first design and technical mainte nance of exhaust systems falls in the lap of the plant maintenance or engineering de partment, and the above books handle these aspects thoroughly. Little has been written however, directly for the safety engineer. What are his responsibilities? What is his role, when the engineering phases are handled by the plant engineer? This data sheet is written for the safety ragineer. It does not cover detailed design, instrumentation or maintenance. It contains only such background principles, and com ments oa popular fallacies, as are needed for, the safety man to work profitably with the engineer and department supervisor. What Can Safety Engineer Do About Exhaust Systems? 1. Air samples; Exhaust systems that arc meant to control a health hazard succeed or fail according to how well they keep the air contamination in the workroom below dan gerous levels. Usually this can be deter mined only by air samples and analyses that actually measure the amount of the harmful agent in the air. Method used varies accord ing to whether the material is silica dust, or other toxic dust; vapor, as from a solvent or degreaser; fume, as from welding; gas: or even hot air--for the latter can be classed as a contaminant, and exhausted to the out doors. When the plant has no full-time industrial hygienist, as most plants do not, the safety engineer should arrange for these tests. They axe his responsibility rather than that of the plant engineering department. Such tests are not needed when the con taminant is not harmful, as with wood dust lime, coal, and other nontoxic materials. 2. Plan: For existing exhaust systems the safety engineer should get a simple sketch of the layout. 1 his need not be a working blueprint or even to scale. An example of a simple line drawing is given in the data sheet All that needs to be shown is the order in which brandies come off the main ducts, diameters of ail ducts, arrangement of fan and collector, size of fan and motor, and if possible, overall rate of air flow* and static pressure as specified by the designer of the system. Filter resistance (J)-(H) 3.0 Material collected Hours of Interval between ?ince last check_______________ lbs. operation-------------------- rcg. shakings-------- t.'omments of men, and Your comments (use back, if necessary*) :------------------- . hrs. . Test holes: In each branch, near the hoods, at the collector intake, and at the fan intake, the safety engineer should have simple test holes, about A" in diameter, drilled. These should be numbered serially with ;atn: or tags, and on his sketch of the piping he should mark the approximate lo cation of each hole, with its number. 4. Portoble U-tube: He should then equip tumself with a U-tube or water manometer. After connecting one leg of the manometer :o a piece of rubber tubing, he can hold the :her end of the tubing over each test hole :r. order and measure the static pressure or action. If the system is new, he should sec that :he plant engineering department `'balances" the air flow from each branch--which means that the correct amount of air flow, as called for by the designer, is passing through each branch. If the contaminant is a health haz ard. air samples, taken after balancing the system, will tell the safety engineer whether control of the air pollution has in fact been established. From then on, assuming no ranges are made in the hoods, piping or process, he can be assured that the equipment is continuing to work right, if rechecks at .he test holes give him the same static pres sure readings as the initial ones. Recheeks with the U-tube should be made regularly, probably at intervals of not over a month. He should Ixave a mimeographed form to record permanently the current readings, so they can be compared with the initial readings. These suction rechecks make it unnecessary to take frequent air samples. Certain other defects, which can be checked merely by looking should be noted: bent or battered hoods, new* branches that may have been added, changes in the process, etc. 5. Meaning of U-tubc readings: Knowing what the static pressures were when the system was properly balanced, changes from these values show if and where trouble develops. For example: The increased reading in the first branch, with other readings remaining normal, shows something is plugging that branch between the test hole and hood. A decreased reading in the branch would mean there is some obstruction farther up the branch, that is, between the test hole and the main duct or header. Decreased readings in several branches and near normal readings would result if the header was partially plugged in branches nearer the dust collector when the header leading to the collector becomes plugged. There will be increiscd readings on both sides of the collector. A partly plugged arrester would result in a decreased reading upstream and an in creased reading downstream. Decreased fan capacity* due to slipping fan belt, dirty* r worn blades, disjointed pipe between fan and arrester, or an open clean out door would give the decreased suction readings throughout the system. Thus relative changes in readings at dif ferent test holes can be used to track down the trouble. Certain absolute values are important too. For example, although suction at a hood is