Heavy-walled cells protect laboratory work at high pressures Control panels
I
R. W. CAIRNS and JACK BARSHA Hercules Powder Co., Wilimington, Del.
Integration of Safety Principles into a Development Program Establishment of safe principles for making and using new products should be an integral part of a development program
'SAFETY
is an important factor, which must be taken into account in evaluating the chance of success and the cost of developing a new chemical process or product. A chemical process is developed usually in fairly definite steps or phases, as it proceeds from the original idea to plant construction and commercial sales. I t is essential that the process development program be accompanied by a parallel program of market development to ensure commercial as well as technical success.
Safety in the Laboratory At all stages of the project good safety practices should be incorporated into a process development program. Even in the laboratory, many questions must be answered and precautions taken to ensure safety of personnel and facilities. T h e answers to these questions may come from the literature, they may be readily determinable experimentally, or they may be inferred from Mhat is known about similar compounds or similar reactions. Thus, a safety-conscious research chemist working in the laboratory with flammable solvents uses steam or enclosed electrical heaters to avoid ignition of any solvent that may escape. When prepar-
1728
ing new compounds whose known analogs are unstable-for example, nitrate esters, nitro compounds, ether peroxides-he assumes that his new compounds are unstable and takes appropriate precautions. If he plans extensive work with his potentially unstable compounds, he has them tested for stability to heat and impact and replaces his assumptions by exact knowledge. \\'hen the answers are not readily obtainable, questions may sometimes be deferred until the project looks promising enough to warrant the effort required to obtain the answers. In the absence of exact knowledge on the safety of a chemical reaction or product, the investigator takes precautions to prevent injury to himself and others if something goes wrong. The precautions include working with small quantities, and using personal protection equipment, fume hoods, safety shields, and barricades for protection against poisonous fumes, fires, and explosions. Because of the small quantities of materials used, consequences of a mishap are generally confined to the laboratory in which it occurs. When early phases of process and market development give promise of technical and commercial success, consideration should be given to process changes which would reduce or eliminate serious hazards. Thus, a flam-
INDUSTRIAL AND ENGINEERING CHEMISTRY
mable solvent might be replaced by an equally effective solvent of lower flammability. An actual instance of this type of change was encountered in a process in which hexane was satisfactory as a reaction medium. However, when it was decided that filters available in the pilot plant and commercial plant \vere not suitable for handling hexane, the process was returned to the development laboratory for selection of a higher boiling reaction medium.
Transition to Pilot-Plant Operation Mrhen the laboratory stage of development is successfully completed. the development program moves on to the next stage-design and operation of a pilot plant. Here the investigator is confronted with a whole series of questions on safety (7), some of which have already been answered in the laboratory. However, many of the safetv problems which arise in setting u p a pilot plant are due to the mass effects which result from the greatly increased scale of operation. At this point safety questions can no longer be deferred, because this is the stage in which much of the information needed for the design of a full-size commercial plant is obtained and a firm economic evaluation of the new process is made. If the process is hazardous, the necessary
Rear view of heavy-walled laboratory cells for high pressure work Operation by remote control protects personnel in high-pressure pilot plant operations
Interior of heavy-walled cell for highpressure pilot plant operations
By-product hydrogen sulfide is burned in a furnace and acidic products are absorbed in water and neutralized
safety features may represent a significant part of plant cost and may affect the decision to proceed with commercial exploitation. Unlike the laboratory, the pilot plant cannot always confine the consequences of a major mishap. Safety features must therefore be designed to cope with all known hazards before the pilot plant is put into operation. Additional safety features must be added as new hazards are discovered in operation. However, the pilot plant is an interim unit. Common sense must be used to prevent delays and expense which can be avoided by alternative but fully adequate arrangements-for example, use of nonexplosionproof electrical gear in homemade vapor-tight housings instead of regular commercial explosionproof units, or the location of nonexplosionproof electrical equipment a t a remote point. Failure to provide adequate safety measures in the pilot plant can cause tragic loss of lives and property. Failure to recognize hazards a t this stage may cause even greater losses when the commercial unit goes into operation. If the company finds safety measures inadequate before an accident occurs in the pilot plant, it may be faced with the alternatives of making additional investment in plant, or, if the added investment makes the process uneconomic, of writing off the money spent u p to this point. The first step in making the transition from the laboratory to the pilot plant is to draw u p a flowsheet showing all the substances entering and leaving the process, basic operations, and the conditions (such as temperature and pressure) under which they must be carried out. Then chemists, engineers, toxicologists, and safety specialists combine efforts to characterize all the substances, equipment, and procedures used according to their ability to produce hazards, such as
combustion, explosion, corrosion, and toxicity. This thorough characterization must answer such questions as: What materials of construction will provide required resistance to corrosion, heat, and pressure? What is the flash point of each substance used? What are the limits of flammability of each substance a t the expected conditions of temperature and pressure? Are finely divided solids present under conditions that can produce a dust explosion? If flammable compositions of vapors or dusts can occur, what pressures and rates of pressure rise can be produced by combustion? What is the toxicity of each substance used? The reaction conditions must be critically examined to detect any new or unusual hazards. This analysis must give the answers to such questions as: What new chemical situations can be caused by malfunction of equipment or by an operator’s mistake? Is the reaction exothermic? If so, how much heat is liberated, how can the heat be dissipated, and what can be done to prevent a runaway reaction? Does the reaction have an induction period? Are any unstable, intermediate compounds formed? For instance, air oxidations are reactions with induction periods and hazardous unstable intermediates. Build-up of peroxides followed by accelerated decomposition becomes much more serious as the quantities are increased. Changes in reactant purity and incidental contaminants in going from laboratory to pilot plant operation can markedly change the chemical behavior of such reactions. When the process has been analyzed
step by step and all the hazards have been determined, the engineers can start to design the pilot plant. With a knowledge of the hazards in all phases of the original process, the first step may involve consideration of changes to minimize or eliminate specific known hazards-for example, replacement of a batch process by a continuous process for better temperature control, or reduction in the quantity of hazardous chemicals held u p in the process. However, even a continuous process may have its own special hazards. Thus, safeguards must be provided to ensure that accidental stoppage of a chemical stream entering the reaction zone does not result in dangerous accumulation of other chemicals which can react violently when the stoppage is eliminated. Reliable, “fail safe” instrumentation is a n important safety feature in this type of operation. When proposals for process changes have been settled, the remaining hazards can be attacked. Basic proved methods are used to cope with common, wellknown hazards-explosionproof electrical equipment or remote location of nonexplosionproof devices to avoid ignition of flammable vapors and dusts; pressure-relief devices to vent excessive pressure; flame arrestors in pipelines; choice of adequate safety factors in design to contain runaway reactions. Isolation by barricading and operation by remote control protect personnel and plant in operations involving high pressures or materials which are pyrophoric, explosive, or radioactive.
Disposal of Volatile By-products Disposal of volatile by-products presents another problem. I n the laboratory, operation in a hood usually solves this problem. However, the much larger quantities of materials involved in pilot plant operations make it necessary to prevent the discharge into the atmosphere of any smok:, foul-smelling, or toxic materials which would create a hazard or nuisance within the plant or in neighboring areas. For example, by-product hydrogen sulfide is burned in a gas-heated furnace and the acidic products are absorbed in water and neutralized. Nitration also requires effective fume control in large scale operation. Steps must also be taken, even on a pilot plant scale, to make sure that liquid wastes are disposed of in conformity with stream pollution laws. T h e tremendous increase in the scale of operations in the transition from laboratory to pilot plant introduces new hazards, or greatly magnifies minor hazards. T h e large increase in the mass of ingredients involved in a chemical reaction may materially alter the course of the reaction and the nature of the products. The pilot plant designers must study the laboratory results carefully to
1730
anticipate these mass effects and provide necessary countermeasures. In dealing with an exothermic reaction, for example, plenty of cooling capacity should be provided to keep the reaction always under control. The engineer must be fully aware of the disproportionate increase in thermal hazards due solely to mass effects. Slower heat conduction in larger equipment caused by the reduction in ratio of cooling area to volume may lead to unexpectedly high temperature rises and runawav reactions.
T h e greatest problem for the designer is the devising of methods to cope with such new and unusual hazards. But, as DeLuca (2) has stated, these very hazards, if solved and brought under control, bring an attractive return on investment and discourage less courageous competitors. Development of a safe and practical process for the manufacture of tetraethyllead is a well-known example. Many serious accidents involving personnel and property in chemical operations have been directly caused by design deficiencies. However, other accidents in chemical industry have been caused by a wide variety of nonchemical hazards (3). Safeguards must be provided -for example, guarding of moving machine parts, safe materials handling equipment, adequate lighting. When design of the pilot plant is completed and construction is under way, it is time to write an operating manual which contains a full flowsheet of the process, complete operating instructions: instructions for dealing with all possible hazards and operating emergencies, and first-aid instructions for treating specific injuries or illnesses. Upon completion of the pilot plant, the operating creiv must be thoroughly trained in its operation, with special emphasis on procedures for dealing with emergencies. T h e pilot plant is still an experimental unit and the initial operations must be conducted with great care. I n many cases, both design and operating procedure will be altered as actual operation provides new technical information or uncovers new hazards.
accumulated in all phases of the market development program. Ultimately, the information must be complete enough to tell the producer how the product can be used safely in any potential customer’s process and to assure him that the new product by itself or in likely combination with other materials will not harm the ultimate consumers, who may be the general public. Particular attention must be given to ensure compliance with government regulations on products (such as insecticides, food preservatives, or food packaging materials) which will be brought directl>- or indirectly into contact with food. Some of the properties affecting safety in use will have been determined during process development; others may be specifically determined by small-scale laboratory tests. I n many cases: the safety of the new product in specific uses must ultimately be determined by actual use tests on a large scale. Thus, wear tests by scores of people are frequently run to determine whether a new textile dye or synthetic fiber causes dermatitis. T h e thermal stability of a new chemical intcnded as a rubber compounding ingredient is verified by carefully controlled larg-e scale tests. The developer ol a new product must be on the lookout for unexpected mass effects which might occur in carrying product applications from the laboratory to plant scale trials. For example, a textile treating agent ivhich works \vel1 in the laboratory when applied hot to small pieces of cloth might. on a plant scale, require cooling of the treated cloth before it is rolled up, to prevent combustion in the large rolls of cloth. Finally, proper containers must be chosen, to ensure compliance with ICC regulations. T h e knowledge that a producL has dangerous properties does not automatically bar it from the marker. One need only point to the explosives and insccticidc industries to realize the truth of this statement. Millions of gallons of toxic and flammable solvents are handled safely by industry each year, thanks to exact knoirledge of the potential hazards of the products and education of the consumers in methods for using them safely.
Safe Use of Products
Literature Cited
Coping with N e w Hazards
No consideration of the application of safetv principles to a development program could be complete without careful attention to the safe usage of the product. T o be commercially successful. a ne% product must sell a t the right price and have properties that qualify it for certain uses. Properties which must be evaluated are those which may create hazards in use, such as chronic and acute toxicity, flammability, and chemical stability. Information on this subject should be
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
(1) Braham, J. E.: ‘Ujg. Chml‘.it 19: 501-4 (1948). Fla., April 1957.
