Industrial Hygiene Digest August, 1967 Cecropia moths.

TABLE 4 ( QUESTIONNAIRE DATA ) EXPOSURE GROUP 1 "DYSPNEA OP BFFORT" AGE <30 30 - 49 50+ 21% 23% 36% 2 23% 18% 41% 3 15% 32% 27% TABLE 5 ( QUESTIONNAIRE DATA ) "WHEEZING" BXPOSURE GROUP <30 AGB 30-- 49 1 37% 19% 2 23% 18% 3 5% 11% 50+ 29% 22% 33% 9. 1H3

Fig 8-13 --``Walking safetv poster " Construction supenntendent lets workers select own safety message, pl.ice it on their own safety hat Courtesy Stone O Webster Engineering Cory Sixty-nine per cent of the respondents in the Council's poster survey preferred posters of 8'/> by 11V^ in and 17 by 23 in size Of these two sizes, the smaller was preferred six-to-one over the larger Types of posters Posters available from the National Safety Council, insurance companies, associations, and other sources fall into two broad cate gories general and special mdustrv(or special hazard) The general posters are concerned with such subjects as chance-taking, disregarding safety rules, forgetting to replace guards, and other human failures Special industry posters, as the term in dicates, have application only in specific industries, such as mining or logging Special hazard posters, for example on lifting, ladders, the storage or handling of flammable liquids, are useful in every industry where the particular hazards are encountered In some cases, a hazard is so serious that a special poster is developed because of the seventy and not the frequency of exposure The National Safety Council carries over WOO different safetv posters in stock at any one time These range from pocket-size pressure-sensitized stickers to billboardsize jumbo posters About 15 new posters are added each month Subject matter is roughly in proportion to the occurrence of certain types of accidents For example, more posters are concerned with materials handling than with chemicals and gases (For illustrations of the many posters available from the National Safety Council, see the CataloglPoster Directory) Other locations Posters and stickers can be mounted on deliverv trucks, industrial trucks, mail trucks and carts, in elevators, and even on doors Pocket cards or plastic pocket protectors, such as those available from the National Safety Council, might be called "walking safety posters " (See Fig 8-13 ) Other materials Safety messages need not be limited to printing and artwork They can be very effective when used m illuminated or changable signs, or even embossed on bncks (See Fig 8-14 ) One company paints a safety message on a plywood welding screen Homemade posters A company can develop its own posters to deal with special Fig 8-14 --Safety messages can even be embossed on bncks Courtesy Domtar Construction Materials Ltd 189

22 Personal protective equipment required7 (Protective glasses safety shoes safety hat safety belt).

Fig 16-4 -- The new layout greatly reduced the hazards, incidental to materials handling in this transformer manufacturing operation handling of materials, many unnecessary movements, and result m bad housekeeping -- in itself a prolific source of accidents Insufficient headroom at aisles, platforms, pipelines, overhead conveyors, other parts of the structure, and other installations is disclosed in studying the models A vertical distance of at least 7 ft generally is specified between passageways and stairways, and overhead structures to provide ample clear ance Overhead cranes and conveyors re quire at least 24 m of vertical and hori zontal clearance Trucks and other vehicles require enough room for movement without endangering men and equipment and need space to back and tum near machines Aisles should be wide enough to permit trucks to pass without colliding For one-way traffic, aisles should be not less than 3 ft wider than the widest vehicles Aisles for two-way traffic should be not less than 3 ft wider than twice the width of the widest vehicle These minimum widths are exceeded considerably m some new build ings where, because of anticipated heavy traffic, aisles from 12 to 20 ft wide have been specified Safe layout of aisles requires that there be no blind comers and that adequate radius be provided to allow for vehicle turns A 6-ft radius is large enough for small industrial trucks Aisles should be clearly defined with ap proved markings of either traffic paint or strip ing material Follow ASI Standard Z53 1, Safety Color Code for Marking Physical Hazards and the Identification of Certain Equipment Plastic buttons that are glued or fastened with metal fasteners to the floor are used by many because of their durability 401

Detailed engineering specifications should be acquired for each machine or structure For machinery, these give dimensions, weights, sizes of plant service connections, lubncation requirements, details on bearings, and power transmission or motor drive data For buildings they include data on general layout, services available, floor load capa cities, ceiling clearances, column spacing, and many other features After a supervisor has made an analysis of his maintenance responsibilities, an organi zation chart should be formulated for the selection and safe assignment of workers The safety man helps in this Such a chart gives the supervisor a comprehensive picture of his force, pointing out the status of trained keymen and reserves Outside specialists who can be called in for unusual or very hazardous jobs should be listed In layoff periods or m emergencies when men are needed in a hurry, this information is quite valuable Work control is necessary for efficient and safe maintenance operation and involves planning, scheduling, and follow-up of the job A smooth-flowing paper work system will help to control each job all the way Work plans should indicate the nature of each job, how it is to be done, the material needed, and the safety precautions required The type of records that should be kept will depend on plant operations, operating time of machines, number of maintenance crews, and schedules A work schedule is successful only if there is a follow-up system to see that it is being adhered to and to determine reasons for de lay Delays may be an indication of faulty materials or wrong procedures Where work schedules are rigid, it is better to hire ad ditional help than to increase the work tempo of the crew Equipment inspections An inspection schedule based on the po tential trouble points listed on maintenance records is essential to preventive mainten ance The schedule can be determined by the number of inspection reports turned m by regular full-time inspectors or by the men of the maintenance crews An inspector must know what to look for He must be something of an expert on, or at least thoroughly familiar with, the equipment under his care This knowledge is partic ularly important for electrical equipment inspectors Electrical equipment usually gives few obvious indications of impending trouble, and is likely to stop altogether with little advance warning Mechanical equip ment often warns of deterioration by such easily recognized signs as noise, unusual appearances, or substandard output But there are some warnings that are more subtle It is important that inspectors be equipped with suitable instruments for making their observations While there is no difficulty in recognizing burned contacts on a motor starter or in hearing the pounding of a worn gear, checking insulation resistance of a motor or measuring the wear on a shaft re quires the correct instruments Personal protective equipment Maintenance men should dress properly for their specific job Garments should be snug-fitting, with a few small pockets Breast pockets are often sewn closed to prevent items from dropping into machinery or in accessible places when the wearer leans over Rings, watch chains, wnstwatches, and other jewelry should not be wom Neckties and loose clothing should not be worn by maintenance men Loose rags must be kept clear of moving machinery If a man carries so few tools that he does not need a tool bag, he should wear a special belt fitted with tool earners To prevent back and spine injuries in case the worker should fall, tools should be earned at the side instead of m the back portion of the belt Gloves or hand leathers should be worn by a man handling rough or sharp objects Welding gloves, rubber gloves for electrical insulation, and rubber gloves for handling acids should be used as needed, but never worn around moving machinery Goggles should be m every maintenance tool kit Moreover, unless the repairman knows the exact conditions he is to work under, his equipment should include several tvpes of goggles to provide protection against flying objects and molten metal, injurious heat and light rays, dust and wind, and acid splashes When a man needs to work in high places or to enter a manhole, bin, or tank, he should wear a life belt, with the lifeline either at- 463

will not slip from his grasp If this is not practical, he could use a rope sling or other device that will give him a positive grip Most strains and back injuries occur when lifting and setting down objects by hand It is important that those who do this work be trained in the proper lifting techniques if these injuries are to be reduced (See Fig 19-1, a model for use in training is shown m Chapter 10) 1 Consider the size, weight, and shape of the object to be earned Do not lift more than can be handled comfortably If neces sary, get help 2 Set feet solidly One foot can be slightly ahead of the other for increased effective ness Feet should be far enough apart to give good balance and stability (approxi mately the width of the shoulders) 3 Get as close to the load as possible Bend legs about 90 degrees at the knees Crouch, do not squat It takes about twice as much effort to get up from a squat 4 Keep the back as straight as possible It may be far from being vertical, but it should not be arched Bend at the hips, not the middle of the back 5 Grip the object firmly Maintain that gnp while lifting and carrying Before chang ing or adjusting this gnp, set the object down again 6 Straighten the legs to lift the object, and at the same time bnng the back to a vertical position Tucking your chin in helps keep your spine straight and firm 7 Never carry a load that you cannot see over or around Make sure the path of travel is clear Carry the object close to the body 8 Never turn at the waist to change direction or to put an object down Turn the whole body and crouch down to lower the object Gnp the object firmly, keep it close, and keep the back straight (not arched) To keep hands from being pinched against the floor, put one comer of a box or similar object down first, so that the fingers can be removed from under the sides Here are some techniques for specific situa tions 1 If the object is too heavy to be handled by one person, he should get help 2 Before lifting a load to be earned, the worker should consider the distance to be traveled and the length of time he will have to maintain the gnp He should recognize the fact that his gnpping power may tire if he has to carry the load a long distance, especially if he has to climb stairs or ramps 3 To place an object on a bench or table, first set it on edge and push it far enough onto the support to be sure it will not fall Release it gradually as you set it down Move it in place by pushing with the hands and body from m front of the object This method prevents fingers from getting pinched 4 It is especially important that an object placed on a bench or other support be sec urely set so that it will not fall, tip over, or roll off Supports should be correctly placed and strong enough to carry the load Heavy objects, like lathe chucks, dies, and other jigs and fixtures, should be stored at approximately waist height 5 To raise an object above shoulder height, lift it first to waist height Rest the edge of the object on a ledge, stand, or hip Shift hand position so object can be boosted after knees are bent Straighten out knees as object is lifted or shifted to the shoulders 6 To change direction, lift the object to car rying position, and turn the entire body, including the feet Do not twist your body In repetitive work, the person and the material should both be positioned so that the person will not have to twist his body when moving the material 7 To deposit an object manually in a tight space, it is safest to slide it into place with the hands m the clear, rather than to lift it Team lifting and carrying When two or more men must carry a sin gle object, they should adjust the load so that it ndes level and so that each carries an equal part of the load Test lifts can be made before proceeding When two men carry long seebons of pipe or lumber, they should carry on the same shoulder and walk m step Shoulder pads will prevent cutting of the shoulders and help to reduce fatigue 505

Principles of Materials Handling and Storing chines are tilted Spillage of residual oil should be wiped up immediately When a jack develops any defect, it should be repaired by qualified workmen and tested under load before being returned to service Handtrucks, dollies, and wheelbarrows Many t>pes of handtrucks and dollies are available, such as two-wheeled, flat, platform, fox, special racks or dollies, and lift trucks Trucks can be purchased or designed for ob jects of various sizes and kinds Operators should wear gloves and safety shoes Two-wheeled trucks and wheelbarrows should be equipped with knuckle guards to protect against the jamming of hands against door frames or other obstructions Two-wheeled trucks should have brakes Fig 19-7 --Foot brake keeps wheels from slipping while truck is being loaded Springs (arrow) hold brake away from wheels when it is not needed (Fig 19-7) so that the worker need not hold the truck with a foot on the wheel or axle The latter practice causes manv injuries To decrease hazards to toes and feet, wheels should be as far under the truck as possible Wheel guards can be installed on manv types of trucks Tongues of flat trucks should be provided with counterweights, springs, or hooks to hold them vertical when not m use If this is not possible, workers should be trained to leave handles in such a position that they will not be a tripping hazard Equipment should be inspected daily and kept in good repair Repair and maintenance records should be kept to show the condition of each piece of equipment Axles should be kept well-greased The type of truck most suitable for the work at hand should be used No one truck is right for handling all types of material Two-wheeled trucks look as though they should be easy to handle, but there are safe procedures that must be followed 1 Keep the center of gravity of the load as low as possible Place heavy objects below lighter objects When loading trucks, truckers and loaders should keep their feet clear of the wheels 2 Place the load well forward so the weight will be carried by the axle, not by the handles 3 Place the load so it will not slip, shift, or fall Load only to a height that will allow a clear view ahead 4 When a two-wheeled truck or wheelbarrow is loaded in a horizontal position, raise it to traveling position by lifting with the leg muscles and keeping the back straight Ob serve the same principle in setting a loaded truck or wheelbarrow down--the leg mus cles should do the work 5 Let the truck carry the load The operator should only balance and push 6 Never walk backwards with a hand truck 7 When going down an incline, keep truck ahead When going up, keep truck be hind (This advice applies to 4-wheeled as well as 2-wheeled trucks ) 8 Move trucks at a safe speed Do not run Keep truck constantly under control Four-wheeled truck operation follows rules similar to those for two-wheeled trucks Extra emphasis should be placed on proper loading, however Four-wheeled trucks should be evenlv loaded to prevent their tipping Four-wheeled trucks should be pushed rather than pulled, except for a truck that has a fifth wheel and a handle for pulling Trucks should not be loaded so high that operators cannot see where they are going If there are high racks on the truck, two men should move the vehicle --one to guide the front end, the other to guide the back end Handles should be placed at protected places 512

Elevators and Plant Railways pole to move cars bv a locomotive is dangerous under any circumstances and is not recom mended Safe practices It is vital that transportation personnel--as well as all other employees --observe safe practices They can be guided by the very same safety rules observed by all large rail road systems (See Association of American Railroads, Safety Rules for various services ) When plant railway safety problems arise, help and suggestions can be sought from the safety men and operating officers of a plant's connecting railway line Safety meetings and other educational ac tivities should be used to inform plant per sonnel about railway hazards To include all the safe practices required for the safe operation of railway equipment would require a book in itself However, a few of the more important ones are included here 1 Stop and look both ways before crossing any track 2 Expect trains or cars to move at any time, on any track, in either direction 3 Step over rails when crossing tracks Never step, walk, or sit on any rail 4 Never go between moving cars (or cars that may move) for the purpose of adjust ing couplers or for any other purpose (The once common practice of kicking couplers to align them is particularly dangerous ) 5 Give a hand or lamp stop signal and re ceive an acknowledgment of the signal before going between standing engines or cars 6 To close a boxcar door, place one hand on the door handle and the other on the back end of the door 7 Step down from cars --do not jump 8 Never attempt to ride the leading foot board of an engine (This rule applies to all employees, including switchmen ) References American Society of Mechanical Engineers, 345 East 47th St, New York, N Y 10017 ASME Boiler and Pressure Vessel Code, Section III, "Boilers of Locomotives," and Section VIII, "Unfired Pressure Vessels " American Standards Institute, 1430 Broadway, New York, N Y 10018 American Standard Practice for the Inspection of Elevators (Inspectors' Manual), A17 2 Safety Standard for Elevators, Dumbwaiters, Escalators, and Moving Walks, A17 1 (Also published bv American Society of Mechanical Engineers ) Safety Standard for Manlifts, A90 1 Association of American Railroads, 59 East Van Buren Street, Chicago, 111 60605 Engineering Division (American Railwav Engineering Association) Manual of Recommended Practice Safets Section, American Railroads Bldg , 1920 L St N\V , Washington, D C 20036 Safety Rules Governing Maintenance of Equipment and Stores Employees Safety Rules Coverning Maintenance of Way and Structures Employees Safety Rules Governing the Care, Maintenance and Operation of Mechanized Material Handling Equipment Used in Railway Operations Safety Rules Governing Tram, Engine, and Other Transportation Employees Federal Railroad Administration, U S Dept of Transportation, Washington, D C 20590 Laws, Rules and Instructions for Inspection and Testing in Steam Locomotives and Tenders and Their Appurtenances National Bureau of Standards, U S Department of Commerce, Washington, D C 20234 Na tional Electrical Safety Code, NBS Handbook H30 Also adopted as AS1 Standard C2 608

FlC 22-3 --Vacuum-handling truck, carrying newsprint roll m this photo, has canopy guard for operator's protection Truck engine or separate source supplies vacuum ,Courtesy Industrial Truck Dw Clark Equipment Co tion-engine powered truck, although a diesel-powered lift truck has been approved by Underwriters' Laboratories and Factory Mutual for use in hazardous areas Powered industrial trucks should be equip ped with a carbon dioxide fire extinguisher or a gas-pressured dry chemical fire extin guisher, and all operators should be trained in its use Also, an important incidental ad vantage is that the truck-mounted fire extin guisher and trained operator are quickly avail able to combat other fires on the premises Lift trucks Lift trucks that can elevate loads higher than the operator's head, or will operate in areas where stacks are higher than the operator's head, should have substantial overhead guards and load back rest extension (Fig 22-1) If an overhead guard is attached to the rear of the truck body, it should also be at tached to the body in front and not the mast An exception is made for those trucks that have the tilt cylinder as an integral part of the overhead guard construction Fork trucks equipped with a single tilt cy linder should have provisions to avoid in jury to the operator resulting from failure of the cylinder or associated parts Forks should be locked to the carnage, and the fork extension, if used, should be designed to prevent unintentional lifting of the toe or 613

Local Exhaust Systems Control ot Hazardous Processes Role of the safety professional Local Exhaust Systems Parts of a local exhaust system Hoods Ducts Air cleaners--general Air cleaner efficiency Dust arresters Air cleaners for radioactive dusts Air cleaners for fumes and smokes Air cleaners for gases and vapors Fans Fire prevention considerations Checking performance Exhausts for Special Operations Open-surface tanks Spray booths Fume control for electric welding Dust control in foundries Grinding operations Woodworking Cast iron machining Oil mist Melting furnaces Materials conveying Internal combustion engine ventilation Fog removal Kitchen range hoods Recirculation of "cleaned" air References Chapter 29 S52 854 881 894 851

Local Exhaust System useful material is held to a minimum (Fig 29-19) Internal combustion engine ventilation Gasoline, diesel, and natural gas engines are being used in increasing numbers and sizes inside factory buildings They are run not only in garages, where maintenance checks and repairs are made, but also in ware houses, storage spaces, loading docks, aisleways, and other indoor areas They are being used as drives for air conditioning and electric generating equipment Their products of combustion contain toxic materials alde hydes, carbon monoxide, and nitrogen oxides The threshold limit for aldehydes in air is only 5 parts per million (ppm) They may be generated if the engine is m poor operating condition, is burning oil, or has a smoky ex haust Usually, however, they are of less importance, from the industrial hygiene standpoint, than the carbon monoxide re leased For an 8-hour exposure, the permissible limit of carbon monoxide gas in air is 50 ppm, but a ventilating system should be designed to keep a much lower level of carbon mon oxide (CO) This value should not be over 250 ppm of CO for one hour's exposure Exhaust gases as released from a gasoline engine 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 exhaust gases will contain about 3 per cent CO When idling, they may contain over 10 per cent Gasoline engines are built m many sizes, ranging from fractional to more than 200 hp Lift trucks commonly have a maximum delivery of 35 to 50 hp Since the engine normally discharges about one cubic foot per minute of exhaust gases per operating horse power, a lift truck when operating near its maximum rated horsepower would release 0 03 times 50 or 1 5 cfm CO The quantity of fresh air that would be needed to dilute this CO output so the concentration would be be low the threshold limit value would depend on many factors (See "References" at end of this chapter Dept of National Health and Welfare, Michigan Health Department, and Milton Shembaum) 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 exces sive levels m an aisle when a truck is doing a stacking operation there, and still be negli gible along the central runway Such a situa tion can best be solved by introducing the fresh air by a duct having discharge grilles m the pocketed regions, rather than along the central runway The latter generally receives adequate ventilation from the building doors Improvement is sometimes made by ex tending the tailpipe of a warehouse truck up ward so it discharges vertically at a point above the operator's head This solution is effective, too, m a situation where a dump truck backs up to a pit hopper, at the bottom of which there may be a conveyor Some times a man stands across the pit where the conveyor controls are located and he can get the full blast of the truck exhaust A vertical discharge pipe would prevent this There are areas where it may not be prac tical or economical to ventilate for the preven tion of objectionable concentrations of 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 Three-inch flexible ducts are fitted over the tailpipes The flex ible ducts join 4-m branches, which in turn are connected to a header located below floor level or overhead Exhaust requirements are shown in Table 29-G The fan should be capable of exhausting the required air volume at l'/ in static pres sure, water gauge For general garage ventilation, where cars are in motion or are idling outside of the re pair 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.

tion The danger is particularly great in hot weather when he is sweaty He should develop the habit of keeping his body insulated from both the work and the metal electrode and holder He should never permit the bare metal part of an elec trode, the electrode insulation, or any metal part of the electrode holder to touch either his bare skin or any wet covering on his body Consistent use of well insulated electrode holders and cables, dry clothing on the hands and body, and insulation from ground will be helpful in preventing contact Some specific precautions for prevention of electnc shock are 1 In confined places, cover or arrange cables to prevent contact with falling sparks 2 Never change electrodes with bare hands or wet gloves, or when standing on wet floors or grounded surfaces 3 Ground the frames of welding units, port able or stationary, m accordance with the National Electrical Code With a small welding unit, a primary cable containing an extra conductor, one end of which is attached to the frame of the welding unit, can be used By means of the proper po larized plug, this ground connection can be earned back to the permanently grounded connection in the receptacle of the power supply 4 Arrange receptacles of power cables for portable welding units so that it is impos sible to remove the plug without opening the power supply switch, or use plugs and receptacles which have been approved to break full load circuits of the unit 5 If a cable (either work lead or electrode lead) becomes wom, exposing bare con ductors, cover the exposed portion with rubber, plastic, or friction tape equivalent to the cable covenng 6 Keep welding cables dry and free of grease and oil to prevent premature breakdown of the insulation 7 Suspend cables on substantial overhead supports if the cables must be run some distance from the welding unit Protect cables that must be laid on the floor or ground so that they will not interfere with safe passage or become damaged or en tangled 8 Take special care to keep welding cables away from power supply cables or hightension wires Gas-shielded arc welding Gas-shielded arc welding (Fig 31-8) is used for joining all types of metals and cast ings In gas-shielded methods, only one electrode is used A gas or gas mixture is in troduced through the torch to surround the electrode and the welding point like a shield The gas cone protects the molten weld pud dle from the atmosphere and stops oxidation of the base metal The electrode conducts either alternating or direct current to provide heat Tungsten arc In gas-shielded tungsten arc welding, the electrode does not melt and is not used for filler metal The electrode is tungsten, which is highly resistant to heat and non-consumable m the welding process Metal arc.

Welding and Cutting TABLE 31-B FILTER LENS SHADE NUMBERS FOR VARIOUS WELDING AND CUTTING OPERATIONS (WELDER AND HELPERS) Type of Operation Recommended Shade Number Resistance welding, and for protection against stray light from nearby welding and cutting (if persons are out of the danger zone) Clear or filters up to No 2 Torch brazing or soldering 3 to 4 Light oxygen cutting and gas welding (to '/a in ) 4 or 5 Oxygen cutting, medium gas welding (Vs to 'A in ) and arc welding up to 30 amps 5 or 6 Heavy gas welding (over '/* in) and arc welding and cutting from 30 to 75 amps 6 or 8 Arc welding and cutting from 75 to 200 amps 10 Arc welding and cutting from 200 to 400 amps 12 Arc welding and cutting exceeding 400 amps 14 NOTE Flash goggles should be worn under all arc welding helmets particularly for gas-shielded metal arc welding Adapted from Welding Handbook, 5th ed American Welding Society items should conform to ASI Standard Z2 1, Safety Code for Head, Eye, and Respiratory Protection Table 31-B is a guide for select ing the correct filter lens for various welding and cutting operations Goggles or spec tacles should have side shields Guidance for lens care is given in Chapter 38, "Personal Protective Equipment " Protective clothing Some of the items of protective clothing needed by welders (Fig 31-12) are 1 Flame-resistant gauntlet gloves, except on very light work 2 Aprons of leather, asbestos, or other flameresistant material to withstand radiated heat and sparks 3 For heavy work, fire-resistant leggings, high boots, or similar protection 4 Safety shoes, wherever heavy objects are handled Low-cut shoes with unprotected tops should not be used because of the spark hazard 5 For overhead work, capes or shoulder covers of leather or other suitable mate rial Skull caps of leather or flame-resistant fabric may be worn under helmets to prevent head bums Also, for overhead welding, ear protection (wool or rubber plugs or wire screen protectors) is some times desirable 6 Safety hats or other head protection against sharp or heavy falling objects Operators and other persons working with inert-gas shielded arc welding should keep all parts of the body which could be exposed to the ultraviolet and infrared radiation covered to protect against skin bums and other types of injuries Dark clothing, partic ularly a dark shirt, is preferable to lightcolored clothing in order to reduce reflection to the operator's face underneath the helmet Cotton clothing disintegrates m from one day to two weeks, presumably because of the high ultraviolet radiation from arc welding and cutting Wool or leather clothing, there fore, is preferable to cotton because it is more resistant to deterioration For gas-shielded arc welding, woolen cloth ing is also preferable to cotton It is not readily ignited and protects the welder from changes m temperature Cotton clothing, if used, should be chemically treated to reduce flammabilitv In either case, clothing should be thick enough to keep radiation from pene trating it Outer clothing should be reasonably free from oil and grease Sleeves and collars should be kept buttoned Aprons and overalls should have no pockets, in which sparks could be caught, on the front of them For the same reason, trousers or overalls should not have tumed-up cuffs 944

TABLE 33-B HUMAN RESISTANCE TO ELECTRICAL CURRENT Body Area Resistance (ohms) Dry skin Wet skin Internal body--hand to foot Ear to ear 100,000 to 600,000 1,000 400 to 600 (about) 100 flow, it is measured in ohms Low VOLTAGE is a rather ambiguous term depending upon whether it is being used by a safety engineer, a plant electrician, ora line man For the purposes of this chapter, low voltage is 24 to 600 volts, and "safety" low voltage refers to voltages below 24 volts Electrical Injuries Current flow is the factor that causes injury in electric shock, that is, the seventy of electnc shock is determined by the amount of current flow through the victim (Table 33-A) Expenmental and field data from authontative sources (see references for articles wntten by Charles F Dalziel) indicate that, m general, an alternating current of 100 milliamperes at commercial frequency (60 hz) may be fatal if it passes through the vital organs Similarly, it is estimated that a value of 16 milliamperes is the average current at which an individual can still release himself from an object held by the hand Such current flow may readily be obtained on contact with low-voltage sources of the ordinary lighting or power circuit Because current flow depends on voltage and resistance, these factors are important Other factors affecting the amount of damage done are the parts of the body involved, the duration of current flow through the victim, and the frequency (if alternating current) Resistance to current flow is mainly to be found m the skin surface Callous or dry skin has a fairly high resistance, but a sharp decrease m resistance takes place when the skin is moist (Table 33-B) Once the skin resistance is broken down, the current flows readily through the blood and body tissues Whatever protection is offered by skin re sistance decreases rapidly with increase m voltage High voltage alternating current of 60 Hz causes violent muscular contraction, often so severe that the victim is thrown clear of the circuit Although low voltage also results m mus cular contraction, the effect is not so violent The fact, however, that low voltage often pre vents the victim from freeing himself from the circuit makes exposure to it dangerous Death or injury by electric shock may re sult from the following effects of current on the body 1 Contraction of the chest muscles, which may interfere with breathing to such an extent that death will result from asphyxia tion when the exposure is prolonged 2 Temporary paralysis of the nerve center, which may result in failure of respiration, a condition which often conbnues until long after the vicbm is freed from the cir cuit 3 Interference with normal rhythm of the heart, causing ventricular fibnllabon In this condibon the fibers of the heart mus cles, instead of contrachng in a coordi nated manner, contract separately and at different bmes Blood circulabon ceases and death ensues, since apparently the heart cannot spontaneously recover from this condition It has been esbmated that 100 milliamperes is sufficient to cause ventricular fibnllabon 4 Suspension of heart acbon by muscular contraction (on contact with heavy cur rent) In this case the heart may resume its normal rhythm when the vicbm is freed from the circuit 5 Hemorrhages and destruction of bssues, nerves, and muscles from heat due to heavy current In general, the longer the current flows through the body, the more serious may be the result Considerable current is likely to flow from high-voltage sources, and in gen- 977