C. L. KWAPP
A
A
ENERGY
FUELS
SAFE HANDL New
data j?om
experimental high eneru compounds
applr to processing, storage, and shielding techniques
with new hazards, call for innovations #ew.mchemicals, handlmg methods. Our work is to prepare new '
solid rocket propellants of substantially higher energy than any currently in use. To formulate such propellants, we have synthesized many new high energy compownds, m e of which are very readily ignited. In the early experimental work, until hazards are defined, safety procedures must be much more stringemt than are r e q u i d for most of the c u m n t propellant ingredients. Our problems are both fire and explosion; explosions are generally the greater hazard. So-called accidental explonions or fires are caused hy a source of ignition such as friction, spark, or hot spot. But friction is always with us, and personnel protection must be provided during all operations. Basic in handling high energy propellant ingredients is minimizing quantities. Not only does increased size mske it more difficult to protect the operator, hut it also hampera operations It is convenient to c l a a s i the sakty requirements according to the quantity of material needed in a given operation. For example, in synthesizing a new chemical, preparations at the half-gram level are useful. Allowing for low yields and loses in separations, at least 100 mg. of product will usually be obtained. By using modem analytical instruments, this amount can give sufficient data to characterize the e~mpound. The half-gram quantities require relatively simple safety equipment thmby allowing maximum iiebility in operation-as is needed in.new shthesis work. After a synthesis procedure has been established, it i then possible to use more protective equipment and a more rigid procedure. Samples in the range of 15
grams of propellant can be used to find conditions foi maximum yields, work out separation procedures, and so forth. Following this work, a mnoteantrolled procedure can be set up for preparation of 50 to 100 grams, or even one-pound quantities of materials. Initial Syn-
Am Limitad lo HaIf-Gmm 0wnHH.I
In the synthesis of half-gram quantities, safety shields furnish most of the personnel protection that is needed Gloves, face shields, a good laboratory coat, long metal tongs, and reach mda give added protection. A con. vemient shield is made by placing '/,-inch poly(methy1 methacrylate) s h e p (Plexiglas or Lucite) in lighi metal frames. ThCy can he hung A m double tracks tc completely enclose a bench top or hood area; sliding the shields allows room to work. If the shields are nar. row (of the order of 10 inches), the operator can worh around a shield, thereby protecting his body whik reaching into the bench or hood area. Tests of this type of shield are reportea in the literature (3). The operator should not touch containers holding hazardous material. Accordingly, long metal tongs, reach rods for valve handles, and other devices should be used w h e m r possible. Obviously, any work that would normally require holding the container of hazardous material with one hand and making an operation with another should instead be carried out holding the container with a clamp. I
V O L 5 5 NO. 2 F E B R U A R Y 1 9 6 3
25
Whenever possible, it is of course desirable to use safety containers to confine any explosion and any fragments generated in the explosion. We tested the effectiveness of various safety containers for use with a few grams of high energy materials, as detailed in Table I. Where failure or incipient failure of the shield was noted, allowable quantities were set at a lower amount of high energy material to ensure a safety factor of at least 2 or 3 times. The results can be used for materials other than the test explosive by setting quantity limits based on maximum energy release. For example, a shield adequate for 2 grams of tetranitromethanebutyl of 1200 calories per gram heat of explosion would be allowed a maximum of 1.5 grams of a material having a heat of explosion of 1600 calories per gram. The worst hazard is fragments formed from rupturing containers. Since light fragments are easier to stop than heavier fragments, it is desirable to have reactions carried out in glass or light sheet metal wherever pos-
sible. Il'hen a heavier metal container must be used, some initial barricade inside the normal laboratory shield should be used in order to stop fragments. The shields made from pipe are valuable in barricading reactors and in barricading containers of hazardous materials in many different operations. The symmetry of the cylindrical pipe is important; as is well known, a cylindrical container withstands high pressures better than a rectangular container made of equivalent materials. It should be mentioned that the position of a detonating sample within a shield is very important; if the quantity is large enough to approach the limit of the protective device, it should be positioned a maximum distance from the wall and from the bottom of the container. The tests reported here were made with the explosive charge centered in the test assembly. Preparation of Larger Quantities
In repeat preparations of new$- synthesized materials, it is convenient to prepare quantities of 5 to 15 grams.
SCREEN 0,080-in. wire-6
X 6/in.
0.047-in. wire-10
X 10/in.
I n glass Dewar flask
1
I
0.5 1.O
'
Screen bulged, no rupture. Screen broke, unsatisfactory
I n glass Dewar flask
1.0
Screen bulged, pulverized glass penetrated screen but was stopped by protective clothing
I n glass Dewar flask
0.75
Shield blown apart, unsatisfactory
In test tube within the Dewar
1. 6
Circumferential bulge a t level of charge, no penetration
SHEET 20-gage, galvanized STEEL DEWAR 0.025-in. wall thickness, Type 304 stainless steel SCREEN ~~~~~
0,080-inch wire-6
X 6/in.
Screen bulged, 1 rupture, but all metal fragments contained
I n finger bomb made from 3/8in. i.d. stainless steel tubing, 0,035-in. wall thickness
PIPE 3/4-in. Schedule 80 steel pipe nipple
I n glass vial
0.5
No bulge
3/~-in.Schedule 80 stainless steel pipe, 4 in. long, open ends
I n glass vial
1. O
No bulge
3/4-in. Schedule 80 steel pipe, 8 in. long, open ends
I n glass vial
1, 5
3-in. split, unsatisfactory
2-in. Schedule 80 steel pipe, 6 in. long, capped a t both ends. Four I/An. holes through wall at 90' intervals around middle
In glass vial
ALUMINUM PIPE 27/8-in. long, 3 / 4 n . wall
26
I n finger bomb made of 1/2-in. i.d. stainless steel tubing, 0,065-in. wall thickness
INDUSTRIAL AND ENGINEERING C H E M I S T R Y
1. 5
I
______Dented, did not pierce pipe
Figure 7 . Remotely controlled tongs, installed in armored hoods. Conuentional laboratory buildings can he adapted f o r handling 50gram quantities of propellants with this type of shielding
Figure 2. The operating face of one of the harricade cells. For remote operations, ali electrical controls are placed outside the cell, pneumatic values can he operated from the outside, and many ports are provided for reach rods, control lines, or other means of control
The problems are very s:milar to those of preparing the smaller samples except, of course, heavier barricades are required. An additional point becomes important; if the operation is carried out in a conventional laboratory, the noise of an explosion can be very unpleasant. If the probability of explosion is high, either ear plugs or ear muff-type ear protective devices will reduce the unpleasant noise of the explosion. Even more effective is a drum of rock salt surrounding the reactor-a “thump box.” I n the event of an explosion, the salt very effectively absorbs the energy of the explosion. A thump box for a reactor containing as much as 10 grams of
high energy materials consists of an oil drum extended to about one and one half times normal height, and filled with rock salt. The reactor should be placed in the center of the drum. Even a high-order detonation in the reactor results in only a slight bumping sound. It should be pointed out that it is frequently convenient to subdivide a preparation of 5 to 15 grams into amounts of 1 to 2 grams, thereby reducing the size of protective devices needed in transporting and handling samples. It is important to be very careful in removing such portions or smaller portions for analysis and other purposes. For this purpose long pipets and similar devices are necessary. The heavier shields required for the larger sample size have been evaluated too (Table 11).
’ Charge of C-4, Grams Result Shield Reactor bulged 500-ml. reactor, 316 5 stainless steel, 0.12in. wall thickness
Larger Quantities Require Remote Control
~
500 ml. reactor, 316 stainless steel, 0.12 in. wall thickness
10
Reactor split, a few fragments formed. Fragments retained by a 4-in. Schedule 40 pipe around the reactor
8-in. Schedule 40 pipe
50
No damage
%in. Schedule 40 pipe
100
Very slight bulge
8-in. Schedule 40 pipe
50, in 2-in. pipe
Fragments imbedded in shield, bulged
nipple to create fragments 8-in. Schedule 40 pipe
100, in pipe nipple
Shield split wide
Charge was ignited by a J-2 electric blasting cap. Composition C-4 is a military demolition explosive, 91% RDX. Its heat of explosion is 1165 cal./g.
In handling highly sensitive materials in quantities above 15 grams, all operations must be carried out completely by remote control. Remote control devices developed for radiochemistry work have been adapted to handle a wide variety of experiments. Two are particularly useful. The first is a long torig, mounted in the shield in a ball joint, and is directly controlled by the operator during his work. The device is limited to the 50-gram scale, since it is not practical to use this type of equipment through the heavy concrete walls needed as a barricade for larger scale preparations. The second type is an electrically controlled mechanical arm mounted on a remotely controlled dolly to create essentially a one-armed “robot.” The robot, shown on the first page, is useful for any scale-up operation up to batches of several pounds of propellant. A third type that is in use, but riot at the Esso research laboratories, is the now conventional master-slave manipulators that are widely used in radiochemical laboratories. The master-slave manipulators can be VOL. 5 5
NO. 2 F E B R U A R Y 1 9 6 3
27
mounted through a heavy wall and therefore are useful for large propellant batches. The robot allows more flexibility in that it can be readily moved to a variety of locations, and the control box can be in any position d a t i v e to the robot. The slave hands can be in only one position relative to the operator. There are, of course, other points of comparative usefulneas, and the relative merit of robot versus slave hands will depend upon the particular operation that is of interest. T o date, the robot has been used for all controls and a t e r i a l handling for a small pilot plant. It has assembled small rocket motors and mounted them on the thrust stand for test firing. For hazardous materials up to 50-gram quantities, cmventional laboratories can be used for the preparation of hazardous propellant ingredients, with only relatively simple engineering work required to set up adequate barricades. For example, the armored hoods shown in
would be sure to injure any person present. In contrast, the separated containers will not transmit either fire or explosion from one to the other, and would injure a man only if he were standing directly a t that container. The operating building consists of the armored hood laboratory containing the armored hoods shown (Figure l), five preparation cells of more or less conventional design (Figure 2), an operating corridor containimg test firing instrumentation and preparation instrumentation, and an officeand shop area. An evaluation of types of observation windows was made in order to establish a window design which would be adequate for protection against the explosion of several pounds of high energy propellant. The windows designed for such an operation are shown in Figure 2 and consist of two 4-inch thick panes of poly(methy1 methacrylate) plastic separated by a gap of 4 inches. The panes are separately mounted to prevent transfer
andled. The ns hoods ond cells, and
maintsnrmce e and instrumentation ingredients are s t o d in smaii, partially buried containers. Firing of rockel
congested area
.,
Figure 1 were constructed of '/,-in. steel plate with 1-in. poly(methy1 methacrylate) sheets as the front barricade and observation windows.
of shock from one to the next. Also, a steel plate overlaps the edge of the inner window by 1 inch. This prevents chipping a t the edges, which increases the over-all strength considerably. The window design was tested by an explosion of C-4 explosive, contained in a steel pipe to furnish fragments, at a distance of 5 feet from the window. With 10 pounds of explosive, the Window was severely cracked, but not broken, even though hit by large fragments. At the 20-pound level, both window panes were broken. Accordingly, the window design is considered borderline for the explosion of an amount of propellant equivalent to 10 pounds of C-4 explosive. The relative position of explosion source and window has a large effect, and can be used to '
Propdhnt Handling in Pound Quantities
A facility for quantities to the 10-pound level requires a storage area, barricaded cells for the preparation of propellant ingredients and for mixing propellants to form rocket grains, and finally an area to test-lire rocket motors. Although it is common to test-fire small rocket motors in a barricaded cell similar to those used for the pnparation of propellant ingredients, there are advantages in firing motors in a totally enclosed area. The storage area consists of 20 Containers, the size of large garbage pails, set in the ground 8 feet apart. This design has advantages in low cost of construction, and maximum protection of nearby personnel in the event of an accident in one of the containers. In the usual igloo-type storage area, an explosion is virtually certain to consume all the material within the storage area and 28
I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
AUTHOR C . L. Knabp is a senior Chemist with Esso Research and Enginwing Co., and is tlu project leaah of the Propellant Euduation group.
provide a safety factor; the damage is most severe in areas directly in line with the source of the explosion. Reactors and other possible sources of explosions should then be mounted so that they are not located on a line drawn perpendicular to any window. The cell wall construction was based on information contained in “The Fundamentals of Protective Design,” an Army Corps of Engineers publication. The rocket motor test sphere has several operating advantages. First, it contains the energy and most of the sound of possible motor explosion, thereby decreasing unpleasant noise in the nearby area. Thus rocket motor tests are possible in a congested area where motor firings would not be feasible without total containment of the motor during the test. Second, it allows total containment of any noxious exhaust gases, and makes it possible to absorb the gases in a chemical spray and remove the solution for chemical treatment.
Finally, it allows the pressure surrounding the rocket motor to be varied to determine the effect of lower pressures such as exist in the outer atmosphere. The sphere shell thickness was calculated by a formula developed by F. A. Loving, of the Du Pont Company, from tests of high explosives ( 4 ) . Since the formula was established for explosions without heavy fragments, the sphere was lined with two layers of blast mat, woven from 3/4-inch steel cable, to protect the sphere wall from damage from motor fragments in the event of a detonation. Two layers of blast mat were used-tests showed h e mats to be much less effective in stopping fragments than is generally assumed. Detailed test data were reported in an Armed Service Explosives Safety Board Seminar ( 7 ) . The test sphere has been fitted for a ramp that will allow operation of a robot within the sphere. Remote television is used for observation. It is possible to set up and test-fire a rocket motor without any direct handling by an operator. The feasibility of doing this
has already been demonstrated by test firings of 50gram motors, in which all operations on the test motors were carried out by use of the robot. Testing Sensitivity
As a new propellant or ingredient passes into the development stage, it becomes increasingly important to know the handling hazards. All operations can be set up for remote control, but both the setup and the operation require added time and expense over normal operations. I t would thus be desirable to demonstrate, wherever possible, that a given material is not hazardous in the operation in question. However, because of the varied effects of different types of accidental ignition and statistical variations in ease of ignition, it has not been possible directly to correlate sensitivity tests and degree of hazard in operations. The impact sensitivity test is the most universal test for ignition sensitivity. It is clearly of value, as is shown by its widespread use, but a low sensitivity in this test can conceal a dangerous hazard--.as is becoming well known. Accordingly, it is necessary to run a wide number of tests to evaluate the effect of other methods of ignition. Tests include a variety of means of determining a spontaneous ignition temperature, thermal stability tests, static spark ignition, friction ignition tests, and the card-gap test for determining detonability. The well-known pendulum friction test does not appear to be in general use at the present time, apparently because it actually creates impact as well as friction, and it rates propellant sensitivity about as the impact tester does. I n the new friction tester, a sliding plate creates the friction (2, 5). This test device shows some materials to be much more sensitive than the impact test would indicate. For example, a mixture of NHlC104 with A1 was shown to be friction-sensitive in the sliding bar test and has accidentally ignited several times in the laboratory. Yet the impact sensitivity is 50 kg.-in. (50% point) on an impact tester which gives a 50% point of 25 kg.-in. for tetryl. Other materials of considerably greater impact sensitivity have not ignited in a variety of laboratory operations. It seems evident that the friction test should be used on all materials that are to be handled directly.
REFERENCES
(1) Armed Services Explosive Safety Board, Minutes of 2nd Explosives Safety Seminar on High-Energy Solid Propellants, Redstone Arsenal, July 12-14,1960, (2) Esso Research and Engineering Co., Quarterly Progress Rept. on Advanced Solid Propellants, Cont. DA-30-069ORD-2487, Dec. 11,1959, andMarch 10,1960. (3) Green, Charles, E., Hater, James F., Redstone Arsenal Research Div., Rept. S-18, Cont. DA 01-021-ORD-5135, September 1958. (4) Loving,F. A., IND.ENG.CHEM.49,1744(1957). (5) Richardson, R. H., Allegany Ballistics Laboratory, Rept. ABL/X-47, Cont. NORD 16640, December 1960. VOL. 5 5
NO. 2
FEBRUARY 1963
29
