1962
COMBUSTION AND DEGRADATION PRODUCTS OF
N204 AND UDMH-HYDRAZINE MIXTURES
Mr. Edward G. Robles, Jr.
Regional Environmental Health Laboratory
McClellan AFB, California
In the ever-expanding missile and space vehicle fields, two items: are to the forefront in the mind of the Systems Engineer. These are: specific impulse and fail-safe operation..
Of the various storable liquid propellants, none in common use give higher specific impulse than the hydronitrogens; hence, these are in large supply at present and their procurement increases daily.
In insuring fail-safe operation, the engineers’ desires are most nearly met by the use of hypergolic fuels, (I.e., those which ignite on contact with an oxidizer), which eliminates the need for a complex ignition system with its concomitant weight penalty and Inevitable operational failures.
Again, the hydronitrogens are most desirable from an operational standpoint, since they are hypergolic with almost every oxidizer one can think of, including WFNA, RFNA, hydrogen peroxide and N2O4~
The following remarks are mainly concerned with the Titan II System, which employs a nominal 50-50 mixture of hydrazine and UDMH as fuel, and liquid N2O4 as oxidizer; however, these cannot be considered as restricted to the Titan II, since many other systems use one or more components of this mixture as well. (Table 1). (See next page).
As can plainly be seen, the engineers are quite pleased with the mixture as indicated, and numerous variations thereof..
Unfortunately, nothing is perfect in this world; while it would be most desirable that a third criterion - safety - be met, it is quite obvious that in missile system ‘components, safety comes in a poor third, if at all.
It is necessary, then, since missile crews are definitely non-expendable, that safety be engineered into the program.
Before a problem can be solved, however, it is first necessary that one have some idea of what the problem is. It has been well known for many years that hydrazine., UDMH and N2O4 are corrosive, irritating, and toxic; however, their chemistry is complex and exotic and is not likely to be solved in any simple fashion for a long time to come.
108
TABLE I
Missile Systems Using Ampines
Vehicle Manufacturer Oxidizer Fuel Payload
ABLE Aerofrt IWFNA UDMH Tiros I, Pioneer
I, II, Explorer VI
ABLE STAR Aerojet IRFNA UDMH Transit lB. 2A,
Isp=248 SB, 4A, 4B,
GREB I, II, Courier
IS. LOFTI, INJUN,
FRAAC
DELTAS Aerojet IWFNA UDMH Echo I
IRFNA, UDMH Tiros II, III, IV,
Explorer X, XII, 050
VANGUARD Aerojet IWFNA UDMH Vanguard I, II, III
ATLAS-ABLE Space Tech. N2O4 N2H4 Vernier
Laboratories Igniter (Mono)’
AGENA A Bell. IRFNA UDMH Discoverer I
AGENA B Bell IRFNA UDMH Discoverer II,
BA-5 Series V-VUI, Xi, XIII, XIV,
Midas II,. Samos II
BA-5 Series Discoverer XVII-
XXI, XXIII, XXV,
XXVI, XXIX7 XXXII,
XXXIV; XXXVI,
XXXVIII et seq.
Midas III, IV
Ranger I-A, U, III
AEROBEE 100 Aerojet IRENA UDMH Research Vehicles
L A R Naval Ord. IRFNA UDMH Warhead
Test. Sta.
BOMARC Aerojet IRFNA JP-X Warhead
NA-2 Rocketdyne IRFNA *Hydyne Target Drone
TITAN II Aerojet N2O4 *Aerozine- Warhead;
50 Manned Vehicles
Isp= 259
109
JP-X; Gasoline -UDMH mixture
Hydyne; 60% UDMH; 40% Diethylenetriamine (R) Rocketdyne
*Aerozine-50; 50% Hydrazine, 50% UDMH (R) Aerojet-General
Our efforts have been, not to find all the possible products of these mixtures, but rather to determine the most likely substances to be produced under~two sets of conditions definable as routine and non-routine, and the most likely environmental effects of these products on humans, plants, animals, soil, and water.
Extensive investigations are being performed on these parameters at Meclellen, Wright-Patterson, and other Air Force installations, at various contractor sites, and at many universities throughout the country in an effort to define the hazards and devise effective methods of eliminating them.
The criteria are these:
(1) Routine: Any actual mission-firing of a Titan U or other missile using the indicated mixtures.
(2) Non-routine: Any spill, in the silo or exterior, or any or all of the components of the system.
In routine firing, the main components of the cloud are:
Water
Carbon Dioxide
Carbon Monoxide
Nitrogen
Lesser Components: NO2, N2H4.
The leading edge of the could contains considerable NO2, as would be expected, since in hypergolic ignition the oxidizer is introduced into the nozzle first.
It is rather astounding, but worthy of note, that hydrazine and NO2 coexist in the cloud; since they are hypergolic, it would be expected that they would be mutually destructive and that one or the other might exist, but not both. Experiments, however, have shown that while hydrazine and NO2 do react in the vapor phase, the reaction is slow, requiring hours for completion. Data to this point, however, indicate that UDMH is not ‘present in the cloud or, if present, is in less-than-detectable quantity.
The general environmental hazards occasioned by an actual firing may be divided into two distinct areas:
(1) Gaseous products
(2) Liquid products
The main gaseous product of any concern is Carbon Monoxide, an insidious killer which, being nearly the. same specific gravity as air, remains in solution and in place for some time. While nitrogen is not to be considered as hazardous by itself, it may displace or dilute the air normally present to such an extent that anoxia would result from breathing the mixture, even if carbon monoxide were absent. Carbon dioxide in high concentration presents a typical syndrome characterized by hyperventilation and panic, which is always dangerous. In short, the cloud itself is no place to be, which might be considered as belaboring the obvious. Less obvious, however, Is the fact that this same atmosphere will be present in an underground location for considerable time after an actual firing.
Elementary precautions must be taken when entering an enclosed structure from which any missile has been fired; the atmosphere should be monitored for carbon monoxide, carbon dioxide, and oxygen, as well as for the system components themselves.
Water vapor, of course, presents no hazard; and, under normal conditions, no one would enter a structure until the residual hydrazine and NO2 had either reacted or escaped. If it became necessary to enter a missile silo immediately after a firing or because of some malfunction, it is to be presumed that protective clothing, including self- contained air supply, would be provided.
The major environmental hazards would result, then, from spillage of the missile fuel and/or oxidant either in the silo or on the ground. There is also the possibility of spillage from leaks in the pipelines. In all of these cases the hazards are due primarily to reaction with the soil or on the surface of soil granules, to form a wide and varied assortment of degradation products, some or all of which may be toxic. These may enter surface or ground water supplies to the detriment of vegetation or the human or animal population of an area.
N2O4 of and by itself, is of little moment. It reacts almost instantly with the acid-fixing moiety of the soil, forming nitrates. and nitrites which are beneficial to nearly every type of vegetation. The only requisite is sufficient dilution so that the soil pH is not lowered so drastically as to kill vegetation. N204 and its solutions should not, however, be allowed to drain into surface or ground water supplies, since nitrate as low as 10 ppm may cause methemoglobinemia in infants, and nitrite should In no case exceed 2 ppm.
111
UDMH and Hydrazine, however, with or without N2 04 cause a more severe problem. They are not only toxic. in themselves, but many of their degradation products are also toxic; hence, It Is. not sufficient merely to destroy the hydrazine and UDMH: solutions resulting from their reaction, with soil, air and water must be brought within tolerance limits of every degradation product; this may be a large order. (Table II)
TABLE II
Toxicities and Limits known breakdown products of the system
N2O4 - UDMH, N2E4
Substance Human Plant . Animal - MAC (ppm)
UDMH I,A,L(?) F, P I, A 0.5
N2H4 I,A,L(?) F, P I, A 1
NH3 I F,P I 100
N2O4 I,L,K,B F, P I,L,K,B 5
(CH3)2NH I, L, K, A - - I, L, K,A
CH3NH.2 I, L, K, A - - - I, L, K, A
HCHO I - - I 5
HCN A,B -- A,B 10
HCNO A A 10
CO2 A - - A 5,000
CO A,B - A,B 100
A - Asphyxiation
B - Blood Cell damage or alteration
F - Fertilizer in low concentration
I - Irritant to skin, mucous membranes, and organs
K - Kidney damage
L - Liver damage
P - Poisonous in high concentration
112.
After a recent spill, in which some three gallons of UDMH-hydrazlne mixture was dumped and diluted with water, after six weeks’ elapsed time, UDMH and hydrazine were still present, as were formaldehyde and hydrogen cyanide. Even after neutralization and oxidation with hydrogen peroxide, while the concentrations of UDMH and hydrazine had been reduced effectively to zero, the concentration of formaldehyde was still high. The point here is, that even though it is possible to remove UDMH and hydrazine by oxidation, the by-products may be as offensive as the compounds themselves. Suppose, for a moment, that instead of three gallons, the spill had been three hundred gallons - - or three thousand!
As an example of what might happen, a pipeline in North Africa some five years ago sprung a leak. Before anyone realized what Was happening some three thousand gallons of JP-4 fuel were lost into the soil. Such a spill might appear to be a minor matter; the soil can hold a lot of petroleum. The trouble was that seventeen -wells were being pumped free of fuel - -a process which took about six weeks. There ,was also a matter of damage to plants and livestock to be taken care of. It is unfortunate, but true, that the poorest range steer becomes a prized herd bull the instant that he is killed by anyone’s accident. The Air Force, an industrial concern, or a private individual, pays top prices for animals kiUed in this fashion.
For vegetation, the price is what the traffic ‘will bear, particularly if the soil is poisoned for more than the length of the growing season.
Fortunately, the Jet Fuel did not injure any people; it merely made the water undrinkable for six weeks. Had any components of the Titan II system. been spilled, however, a cause celebre would undoubtedly have resulted, as it would in this country. It cannot be too strongly stressed that these compounds and their degradation products are poisonous until. they have finally been oxidized to nitrates, CO2 and water.
While, from an industrial hygiene standpoint, it. might be pleasant to say, “Spills will not occur, it is best to legislate against the inevitable, and to be prepared against the spills which will occur, understanding that without extensive - and expensive - neutralization, UDMH, hydrazine and N204 may not be allowed to enter surface water, or ground water aquifers. One exception may be noted; the ocean is a reservoir of essentially infinite capacity. Many such compounds may be eliminated by barrelling, weighting, and dumping into the ocean past the continental shelf, provided this is not otherwise prohibited. For Installations close to the coast, this means may be b est. For others, the minimum safety procedures require site selection such that no waste products will enter drinking or irrigation water supplies; failing this requirement, complete treatment facilities and acres of concrete are necessary.
113
For guidance in this matter, it must be remembered that various state water pollution control boards have decreed that no effluent of any industrial process may raise the receiving water above the maximum permissible concentration for any component; therefore, when. UDMH and hydrogen cyanide are the items under consideration, the only criterion possible is complete destruction. Fortunately, hydrogen peroxide and time will eliminate both.
Experiments are currently under way to refine the conditions under which these compounds. may be completely eliminated in den time. Catalytic decomposition seems to give some promise, but. the results are not all in yet. It seems definite, however, that holding ponds are going to be a. must, in order to legislate against the maximum credible accident.
Let us hope that it never occurs, but let us be prepared for it If it ever does.