SAFETY

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The Safety Expert Speaks E x p a n d e d chemical production brings need for more d a t a on potential ly dangerous chemicals

( j R O W T H IN CHEMICAL PRODUCTION and use brings a need for more than expanded plants. As chemicals move from laboratory curiosities to wide in­dustrial use, standards for safe handling of these chemicals become a necessity. According to Mathew M . Braidech, di­rector of research for the National Board of Fire Underwriters, no data are generally available on the ignition, combustion, and toxic properties of many widely used industrial chemicals.

Braidech, as chairman of the ACS Committee on Hazardous Chemicals and Explosives and of the National Fire Protection Association's Committee on Chemicals and Explosives, is alarmed at the numerous requests received by NFPA for safe handling information and recommended handling procedures for chemicals no longer considered rare. Therefore, t h e NFPA group is beginning, with a priority system, to provide needed information.

To get a closer look a t plans to revise and institute standards for handling chemicals, C&EN recently interviewed Braidech.

Question: Mr. Braidech, what does your NFPA Committee on Chemicals and Explosives do?

Answer: The coirimittee develops standards on storage and handling of explosives and chemicals which are flammable, violently reactive or ex­plosive, or which by reason of toxic

or corrosive pi op ei ties may interfere with emergency fiie fighting opeiations.

Q: What will be the committee's main effort during 1956?

A: Our program will include several jobs. Some are:

• To revise NFPA's present Table of Common Hazardous Chemicals and accumulate data on another 1000 po­tentially hazardous chemicals now used industrially.

• To develop technical information for safety recommendations on a grow­ing list of dangerous chemical reactions.

• To prepare a model ordinance for storage and handling of chemicals based on various groupings or classes, including those presenting special and unusual hazards.

• To revise and bring up-to-date the "Quantity and Distance Table" in the NFPA Explosives Ordinance.

• To organize an advisory subcom­mittee of qualified technical personnel to answer queries on chemical prob­lems presented to NFPA.

Q: To cover some of these points in more detail, what type of technical information on dangerous chemicals needs to be expanded?

A: W e need more complete data on those chemicals having an unusual degree of fire and explosion potentials.

Especially needed is information on in­compatible chemicals producing haz­ardous combinations or those which may augment the rapidity and violence of a fire.

Q: Many other hazard factors be­side flash point now are recognized, by safety engineers in handling of hydro­carbon liquids. What are some of these factors?

A: The flash point test provides a simple yardstick to determine some safety requirements in transportation and in storage, yet i t is inadequate. With increased risks from greater ex­posure, temperature, and pressure con­ditions, process development and oper­ating personnel should consider: igoita-bility, flammability, stability, catalytic influences, incompatibility, and toxicity.

Q: Certain chemicals widely vised are very corrosive. What particular problems face chemical plant main­tenance people to ensure that fire fight-

J U N E I I, I 956 C & E N 2 9 1 9

SAFETY

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A : Corrosive chemicals have pro­duced much concern regarding serv­iceability of fire protective equipment such as detection and alarm systems, automatic sprinklers, and COo extin­guishing units. Tremendous mainte­nance is needed to keep fire control equipment in gopd order. More con­sideration should be given t o design of this equipment along t h e l ine of 7; litable corrosion-resistant materials of construction and serviceable protective coatings.

Q : Receiving much attention re­cently is the concept of critical-diam­eter confinement, or storage volume dimensions helotv which heat generated by self-decomposition becomes greater than heat lost through normal cooling processes. How is this concept applied to 'potentially hazardous dry chemicals such as ammonium nitrate?

A : Critical diameter confinenaent— reported in the literature about 15 to 20 years ago—has been brought to the front only recently in the studies con­ducted for the Federal Interagency Council on Ammonium Nitra te , organ­ized to study t h e Texas City Disaster of 1947. R . M. Hainer a n d Warren C. Lothrop of A. D . Little, Inc.,. ha\ e done significant work in this field.

W e know that heated ammonium nitrate undergoes dual dissociation: exothermically into nitrous oxide and water, and, at the same t ime, endo-thermically into ammonia and nitric acid vapor. T h e two concurrent re­actions tend to reach a steady-state temperature. At atmospheric pressures the decomposition is hmited t o a com­paratively moderate rate. A t higher pressures, however, the endothermic dissociation, which absorbs all t h e heat available from the exothermic change, is repressed. A more rapid self-accel­erating exothermic decomposition takes place with at tendant t empera ture rise, and release of gaseous products I n con­siderable volume, until an explosive de­composition rate is attained. T h e acti­vation energy appears t o b e of the order of 50,000 calories per mole.

These studies indicate t h a t hazard­ous self-heating will occur in a confin­ing, unventi lated "critical sphere", of 5 meters radius with chemicalLy pure ni trate at 300° F . , and with a 3 % water-repellent coating (fertilizer grade ammonium nitrate of Texas Ci ty Dis­aster) , this temperature is reduced t o below 212° F .

These investigations also indicate , that for an explosive rate of reaction t o

occur, a min imum temperature of about 840° F. is required and tha t such tem­peratures are not possible without a confining pressure of 900 to 1000 p.s.i . for the straight ammonium ni t ra te . However, for the older type of fertili­zer (conditioned with a resin-petro-latum-parafBn coat ing) , this critical pressure is reduced to 300 p.s.i.

Applying these data to ship explo­sions, w e note that the close-packed geometry within a ship and its l imited venting might have resul ted in an in­ternal pressure rise and unrestricted acceleration of t h e decomposition ra te . This would lead to eventual detonation as occurred on t h e S. S. Grandcamp a n d S. S. High Flyer at Texas City. In t h e case of warehouse ammonium ni t ra te fires, the pressure required for explosive reaction ra te is unattainable, a n d fires have consumed the ammonium ni t ra te without explosion.

However , other evidence ( u n p u b ­lished studies by Army Ordnance ) indi­cates ammonium nitrate can possibly b e de tonated sympathetically by a shock wave resulting from a priming gas phase explosion. Thus, fuel oil on t h e ships reaching hot molten ammonium nitrate m a y have effected an en masse decomposition and subsequent de tona­tion.

Q: W e understand that much thought has been given to a colored hazard-labeling code by fire safety authorities. Can you tell us something about it?

A : T h e r e has been a growing need for a simplified system of grading haz­a rd severity by use of color a n d con­ventional symbols. These symbols would convey information on-the-spot to fire services and help direct proper emergency operations. One N F P A technical committee has a plan for a system under advisement. T h e Com­mittee on Chemicals and Explosives is interested in applying this scheme. This plan involves a grading classifica­t ion into four hazard categories: pres­sure hazard (green) , flammable hazard ( r e d ) , toxic hazard (yellow), and re­active hazard (purp le) . It also in­volves four degrees:

1. Most hazardous 2 . Ordinary hazard 3 . Light hazard 4 . L o w hazard

T h e nature and degree of hazard would b e represented by an appropriately colored circle containing the required numera l . Combinations of hazards could thus be indicated by different segmental colorings within a single circle, wi th numbers to indicate order of severity.

2 9 2 0 C & E N J U N E I I , 1 9 5 6

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SAFETY

Q: What is perhaps the greatest problem from a personnel standpoint in industrial fire fighting?

A: Education of firemen and alert­ing fire protection personnel to the vast amount of information available on hazards. We must bring material on hazards in chemicals to an average fireman at his level of understanding, to make it effective in emergency use.

Q: For example, zvhat information do fire fighters need badly now?

A: A list of commercial trade names covering all flammable a n d hazardous chemicals. Proprietary names do riot reveal the true chemical na ture of such materials. For instance, some 400 dif­ferent chemical solvents may be found listed under 3800 trade names. In­secticides and pesticides containing or-ganophosphate compounds demand ad­vance -warning on the need for use of proper protective equipment by fire­men—letter abbreviations of such preparations are not readily identifi­able. Some producers are placing proper safety information on the labels for this reason.

Q: Who will get the information your committee obtains?

A. In addition to NFPA members, it is available to all industrial safety engineers, plant fire departments, and last but not least, municipal fire depart­ments, state fire marshals, and other in­terested authorities.

Q; What other operational aids do either NFPA or NBFU make avail­able to municipal and plant fire departments?

A: Well, for example, we at NBFU have prepared a special interest bulle­t in telling how to protect firemen £rom toxic insecticidal chemicals during a fire and what procedures to take in posture salvage operations. This re­sulted from two recent, serious fires in warehouses containing organic phos­phate insecticides where firemen were hospitalized from poisoning by the insecticides.

Q: How do 1XFPA and NBFU aid industry and governmental agencies?

A: By collaborative pooling of our fire and explosion safety talents through technical committees made up of a balanced representation of various in­terests concerned. The primary ob­jective is to develop competent stand­ards of good safety practice recom­mendations, and emergency safeguards that will have authoritative status and wide acceptance. α