The chemicals used in the launch of spacecraft can pose exceptionally high dangers to human health. Liquid nitrogen and helium can cause asphyxiation. Liquid oxygen can increase fire hazards by enhancing the inflammability of combustible materials. Liquid hydrogen readily ignites when it is mixed with air. (Nitrogen and helium are not used as fuels, but are employed in the pressurization of tanks.)
Of more concern are the hypergolic propellants, so-called because they ignite spontaneously when mixed with a complementary fuel. What makes these chemicals useful as propellants – their high reactivity – also tends to make them lethal when they come into contact with living organisms.
The Hydrazines
The chemical formulation for basic hydrazine is N2H4. Other hydrazines are monomethylhydrazine (MMH) and 1,1, dimethylhydrazine, also called unsymmetrical dimethylhydrazine (UDMH). Two other closely related chemicals are formed when UDMH decays: formaldehyde dimethylhydrazone and dimethylnitrosamine (DMNA, but also called nitrosodimethylamine, or NDMA), which is produced when UDMH is exposed to air. The following descriptions of the effects of exposure to the hydrazines and to nitrogen tetroxide are drawn from “Medical Manifestations of Exposure to Nitrogen Tetroxide and Hydrazine Propellants,” by Col. Bruce J. Poitrast and Col. Karen A. Meier.1
Hydrazine
“The vapor is highly irritating to eyes, upper respiratory tract and skin. Liquid coming in contact with the eye may cause permanent corneal lesions and severe exposure may result in temporary blindness. The liquid is corrosive. Clinical effects range from severe dermatitis to marked skin edema [swelling] and penetrating burns. Repeated exposures may result in sensitization dermatitis. Systemic exposure may result in dizziness, nausea and anorexia…. Clinical studies show fatty degeneration of liver tissue, depletion of liver glycogen and loss of mitochondrial activity.”2
Monomethylhydrazine
According to Poitrast and Meier, MMH vapors, like those of hydrazine, cause dizziness and nausea at levels of 50 parts per million. MMH can bring on severe anorexia and fatty degeneration of the liver. A blood disorder called methemoglobinemia as well as one called Heinz body formation are known to result from MMH exposures. MMH “also exerts extremely toxic effects on the central nervous system,” Poitrast and Meier write. Animal studies have shown that convulsions are due to the direct action of MMH on the brain. MMH is also a carcinogen suspect.
UDMH
This is a respiratory irritant and causes convulsions. In relatively high concentration, it can cause pulmonary edema. Some animal studies suggest that it might have a cumulative effect. UDMH also is a suspected cancer-causing agent. The DEIS additionally states that it can cause hyperglycemia, which is the presence of abnormally high levels of glucose in the blood.
NDMA (or DMNA).
This “is highly toxic in animals and man…. NDMA poisoning causes nausea, vomiting, abdominal cramps and diarrhea. Other symptoms may include headache, fever, and weakness…. Human cases have been reported to show severe liver damage…. NMDA is a highly potent carcinogen in several animal species, producing malignant tumors of the liver, kidney and lung. To date, a safe exposure standard has not been established. Therefore, all contact with NDMA should be avoided. Exposure to NDMA must always be considered when working with UDMH.”
The DEIS minimizes the risk, noting that NDMA (referred to there as DNMA) is present in cigarette smoke and “a variety of foods including cheeses, soybean oil, canned fruit, meat products, fish products, and alcoholic beverages. Concentrations in these foodstuffs have been measured to be” up to 85 micrograms per kilogram (a microgram is a billionth of a kilogram).
NDMA is one of a family of substances called n-nitrosamines, which, the DEIS notes, “have been shown to be teratogenic [causing abnormal formations], mutagenic [causing genetic changes], and carcinogenic [cancer-causing] in experimental animals…. Some n-nitrosamine substances are capable of inducing tumors after a single dose. …This substance has also been shown to act as a transplacental carcinogen [that is, capable of being transferred from a mother to a fetus] when administered to rats, mice, and hamsters by various routes.” Finally, it notes, “this substance has also been reported to affect male and female reproductive capacity.”3
FDH
Apparently, little is known of the medical effects of formaldehyde dimethylhydrazone. Poitrast and Meier do not mention it. The DEIS does – but only to say that a search of literature on the subject turned up little of value. No standards have been set for exposure to FDH. The DEIS states that “in the absence of toxicological information specific to formaldehyde dimethylhydrazine, it is assumed… that the toxicological properties and acceptable exposure levels of FDH are equivalent to the properties and levels of its parent compound, UDMH.”
Nitrogen Tetroxide
Exposure to nitrogen tetroxide (N2OA) can be lethal. Nitrogen tetroxide exists in equilibrium with nitrogen dioxide, or N02. Exposures to either substance produce identical symptoms, however.
Poitrast and Meier note, “There is some evidence for increased respiratory infection rates even at 1 ppm” exposure to nitrogen tetroxide. “At 25 ppm there is respiratory irritation with cough and chest pain. At 50 ppm there may be development of acute pulmonary edema. At 100 ppm there is acute pulmonary edema and death.” Even mild exposure can bring on disease that can last up to three weeks. Symptoms can include eye irritation and upper airway irritation with fatigue; a cough and cyanosis (lack of oxygen); vomiting, vertigo, and somnolence, as well as loss of blood pressure; and loss of consciousness.
Increased exposure can bring on moderate injury, which Poitrast and Meier say is characterized by any of the symptoms just listed, “plus the development of pulmonary edema in the first 30 hours. The majority of these individuals will recover … but a number will die from the onset of the pulmonary edema.”
Finally, there is “severe disease,” characterized by the development of what is called bronchiolitis fibrosa obliterans, a disease in which the alveoli of the lungs fill and the bronchioles “become surrounded by a fibrous tissue.” This disease, they say, “may even occur, though rarely, in individuals minimally affected at the time of exposure.”
One third of all people exposed to 50 ppm or more of nitrogen tetroxide will not survive, Poitrast and Meier state.
Chronic, low level exposure to nitrogen tetroxide or nitrogen dioxide has been linked with increased susceptibility to respiratory infection by bacteria or virus.
1Published in Medical Bulletin of the U.S. Army Medical Department, February 1988.
2Mitochondria are threadlike bodies found in the cytoplasm of cells. They are essential to cellular function.
3See DEIS, Volume VIII, “Human Health Risk Assessment,” Appendix A, “Toxicological Profiles of Contaminants of Concern,” page A-25.
Volume 4, Number 2 August 1993