P L A N T
O P E R A T I O N
a n d
M A N A G E M E N T
Unloading dock with first-aid cabinet and water shower located close to tank car.
CAUSTIC
The dock is enclosed, and is well lighted.
SODA Safety Practices in Handling
Ι Ν DUST RIAL use of caustic eoda presents
•· numerous safety hazards for the oper ating personnel of the plant. Accord ingly» proper facilities for handling are essential, and appropriate precautions must be observed by chemical operators in transportation and use. The potential number of such hazards is significantly large, since the amount of caustic soda sliipped last year amounted to about 1,750,000 tons. Over half of this quantity was shipped as liquid in tank cars, while the rest was shipped as either solid or flake in steel drums» Each form of caustic soda has its own particular handling problem, and this makes specific safety recommendations for each desirable. Liquid caustic soda is shipped in spe
cially lined tank cars. The more recently designed cars are of welded construction and most of them are provided with ther mal insulation covering the tank. L i q u i d Caustic Soda Shipment Reinforcing straps aid in holding the tank to the car frame. Two safet3'" valves and the discharge valve handle are mounted on the dome of the car. The most recently designed cars operate the valve handle outside the dome. A hinged dome cover provides ease of sampling and venting during gravity unloading of the liquid caustic soda. Safety platform and guard rail protect the operator during the loading and unloading operations. A handrail and safety platform along the sides and ends of the car enable the train crew to handle the car safely. An auxiliary foot valve is located under the
car to prevent drip from the discharge valve located in the center and base of the car. An alternative unloading sys tem for overhead discharge is provided in the form of a 2-inch pipe running from the dome to the bottom of the tank plus a com pressed air connection on the dome. Preliminaries to Tank Car Unloading. The tank car should be spotted on level track and blocked, to prevent any move ment. If there are train movements near by, derail clamps should be attached to the track at least one car length from each end of the tank car, and only the operator should have the derail keys while the car is being unloaded. Regulations signs— "Stop—Tank Car Connected" appearing in blue on a white background—should be plat-od on the track with the derail devices.
C. W . RIPPIE A N D A . H . C O P R L A N D , JR., Diamond Alkali Co., Technical Service Department, Painesville, O h i o 1164
CHEMICAL
A N D ENGINEERING
NEWS
Tank cars of liquid caustic soda should always be unloaded by daylight unless adequate flood lighting is provided for night operation. The storage tank: should have a reason able excess capacity commensurate with the volume of the car or the diluted vol ume of alkaline solution to be unloaded. An adequate vent t o the taak prevents any pressure or vacuusm during filling and emptying of the tank. The top of the storage tank should be on a lower level than the bottom o f the tank car with a control valve closer to the storage tank. Safe connections should be made between the tank car discha-rge valve and the stor age. The dome lid should be opened to vent the car. A rubber—tipped iron probe may be inserted through the dome to detect any solid caustic soda in the tank. If solid caustic soda has formed inside the car it is recommended good practice to puncture before t h e caustic is heated by closed steam coils until all is in liquid form and flows cosily. Tank cars containing 50 per cent liquid caustic soda should never be heated over 100° F. and those containing 70 per cent liquid caustic soda should never be heated over 194° F. An open steam line is never recommended for thawing the car, as the excessive temperatures may injure the special linings. A sample sbould be taken by lowering a nickel tube into the tank. A rubber tube attached to the upper end of the nickel tube is pinched off when maximum depth has been reached, so that a, cross-section sample is obtained., The sampling tube is then raised, robber tube released, and the sample collected in a bottle which is suspended within the dome to protect the operator from any spatters of the liquid. The operator should wear goggles and rubber-covered canvas gloves when he is preparing the car for unloading and during subsequent unloading operations. Addi tional precautions include a safety shower, first-aid kit, and water hose to wash off any spillage o n the car. Gravity Unloading of Tank Car. For gravity unloading, the operator should be sure that the dome lid is open, after which he opens the auxiliary discharge valve under the car and then the discharge valve on top ef t h e car. If the top dis charge valve handle is located inside the
W e l d e d steel storage tanks with retaining wall and sheilds over pumps and motors
dome, the operator should avoid contact with liquid caustic soda inside the dome. The valve near the storage tank is next opened, so that the caustic solution will gravitate into the storage tank. Storage Tanks, Pipes, and Pumps. Welded steel tanks are preferred for caus-
Although the burns are not felt immediately, caustic s o d a is injuniors where ever it makes contact with the skin Protection by goggles and clothing is necessaru. Ρroper precautions and intelligent operation aree s s e n t i a ltothe safe handling and the use of caustic soda When the a c t i o n of caustic s o d a is w e l l understand, adequate safety paractices protect the health of all workers in handling one of A m e r i c a ' s large-tonnage of all VOLUME
22,
NO.
14
»
»
» JULY
3 5,
1944
tic storage with a minimum 0.25-inch thickness in bottom and lower sections for capacities over 12,000 gallons. Although caustic soda solutions very seldom leak from a tank, a retaining wall is a desirable safety precaution in confined areas or in buildings. The temperature of the tank is main tained at least above 55° F. for 50 per cent and 150° F. for 70 per cent caustic soda solutions. Outdoor tanks should be equipped with thermostatically controlled steam coils and vent pipe to equalize tank and atmosphere pressure. Best design of pump for caustic soda is an all-iron open impeller centrifugal type. Pumps under pressure are shielded to control spray if any packing gland fails. Asbestos fiber impregnated with graphite is the most suitable packing material for pumps and hand valves. 1165
Safety clothing, hand rail, and tank cover provide adequate protection in handlingflakecaustic
Pipes joined with companion flange joints give the best over-all service and should be covered with a safety bonnet over each joint. Pressure lubricated plug valves of all-iron construction are recommended. Periodic inspection and cleaning of caustic pipes are important. Cleaning should begin with steaming out of the line, followed by washing with cold water. Repair men should be sure that the pipe is not under pressure before they break open the flange. Such work should be done from above the pipe rather than from below and all spillage must be drained off for disposal. To thaw frozen caustic pipes, the National Safety Council recommends that the line be opened beyond the frozen section and that steam be introduced at the open end and worked back toward the frozen section until the thawing is complete. A second method is to open up the pipe near the frozen section, wrap the frozen section with burlap, and apply steam to this wrapping until the section is completely thawed. The third method is to add warm water at the open end of the pipe by means of a rubber hose. The hose is pushed into the pipe as far as it will go and the flow of water gradually dissolves out the frozen caustic. In all these procedures the resulting caustic solution should be drained off to a safe place. Flake Caustic Soda Most of the hazards associated with solid and flake caustic soda are related to removal from drums and dissolving for use. Flake caustic is easily removed from the drum by scoop or shovel as needed. Flake caustic soda may be shoveled directly from the open drum to the dissolving tank or consuming tank. Mechanical agitation is desirable in the tank 1166
during addition of the chemical to prevent local overheating and consequent possible surging or boiling of the solution from the heat generated. The drum must have its cover tightly in place when it is not in use to prevent absorption of moisture and carbon dioxide from the atmosphere. Open tank or hopper should be provided with adequate cover and hand rail to safeguard the operator. The height of such hand railing is 42 inches or more. Possible spatter of caustic soda from the tank should be anticipated with use of goggles and protective clothing. Solid Caustic Soda Solid caustic soda is removed from the drum by prying open the seams of the drum with a steel bar and stripping the sides and ends off the cake. The metal of the drum is folded away from the solid caustic and the cake is then rolled onto a cradle which transfers it to the dissolving tank by means of a chain hoist. During this operation the cake must rest horizontally to avoid rolling off the cradle. The cake is lowered into the dissolving tank until it rests on a grating situated about 6 inches above the bottom of the tank. If coarse lumps of caustic are required for tower packing, the caustic cake is partially broken up with a sledge by striking the drum along its horizontal axis prior to prying open the seams. After the drum has been removed, the large pieces are broken readily by covering with burlap before using a heavy sledge. The lump caustic should be placed in a tightly closed steel drum if not used immediately. Goggles and protective clothing are necessary during the operations and steel-toed rubber-soled shoes provide added safety. Steaming of Solid Caustic. Solid caustic may be removed from the drum as CHEMICAL
liquid by application of steam and water. Two 0.75-inch holes are punched in the head of the drum at the opposite edges. The drum is hoisted with securely placed grappling hooks and suspended over the dissolving tank at about a 20° angle with head down. A steam line with pressure gage is applied with loose-fit nipple in the upper of the two holes, and steam is bled slowly into the drum until the gage registers about 10 pounds pressure. Liquid caustic soda of about 70 per cent drains from the lower hole under these conditions. This concentration is readily reduced to 50 per cent by bleeding in water with the steam. Flow of caustic solution can be stopped by shutting off steam and water. Another method dissolves the cake by circulation of solution from the tank through the drum. Three holes are punched in the side of the drum and the drum is suspended horizontally over the top of the tank with holes on lower side. Caustic is dissolved from the drum by contact with solution from the bottom of the tank. The solution is continually recirculated by means of a pump applying a stream of solution with a jet system to the caustic cake through the punched holes. Circulation continues until required strength of the solution is attained. Goggles and safety clothing must provide protection against spatter from the tank and drum. Protective Clothing The National Safety Council recommends protective clothing of cotton and rubber for caustic handling operations. Wool and leather are less resistant to caustic soda. Shirts and pants should be cotton, while aprons, gloves, and boots are preferably rubber. Shoes recommended are rubber-soled with steel-reinforced toes. A broad-brimmed hat protects the head and shoulders and goggles are essential at all times. Sleeves cover glove wrists and pants cuffs cover shoe tops in order to prevent any caustic soda from running down the top of the shoes. The first-aid kit must contain eye wasb and body wash solutions and means of application, such as eye glass and sterile cotton. Solutions for eye wash may be 1 per cent ammonium chloride, 4 per cent boric acid, or 2 per cent zinc sulfate. Body wash solution may be saturated magnesium sulfate, 10 per cent ammonium chloride, or 2 per cent zinc sulfate. Where caustic handling hazards are greatest, safety showers provide some first aid, in case a large percentage of clothing is saturated with caustic solution. A bubbler at the water fountain can be used t o flush the eye. Water pails are provided where temporary operations are in prpj^ ress, such as during caustic piping repair. All caustic burns require immediate washing treatments, followed by medical attention as soon as possible. AND
ENGINEERING
NEWS
