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NG [Nitroglycerin ]

Nitroglycerin (NG) [Synonyms: 1,2,3-Propanetriol trinitrate; glycerol trinitrate; nitroglycerol; NG; trinitroglycerol; NTG; trinitrin] is an oily liquid at room temperature; colorless in pure form and pale yellow or brown in commercial form. It is used in manufacture of dynamite, gunpowder, and rocket propellants, and as a therapeutic agent primarily to alleviate angina pectoris. NG is used to make smokeless gun powder and rocket propellants. Single-base powders contain only nitrocellulose, double-base powders contain nitrocellulose and NG, and triple-base powders contain nitrocellulose, NG, and other combustible materials.

In 1847 a new explosive came into being. This was nitroglycerine, made by treating glycerine with nitric and sulphuric acids. But at first it was even more dangerous to handle than guncotton, for the least shock exploded it, and its violence was terrific.

The great chemist Alfred Nobel tried to improve it by mixing it with gunpowder, but the powder did not absorb all the nitroglycerine, and accidents of the most terrible kind became more and more frequent. Yet the new explosive, being liquid, could be poured into crevices in rocks, and was so useful as a blasting agent that its manufacture went on until a large vessel carrying cases of the explosive from Hamburg to Chili blew up at sea. The ship was blown to bits and her crew killed, and the disaster caused so great a sensation that the manufacture of nitroglycerine was prohibited in Sweden, Belgium, and in England. But Nobel still continued his experiments, and at last, after trying sawdust and all other sorts of absorbents in vain, found the perfect absorbent in the shape of keiselguhr-a sort of earth made of fossil shells. The mixture is what we know to-day as dynamite; and in spite of the fact that modern chemistry has produced very many new explosives, some of terrific power, dynamite remains the safest and most widely used of all explosives.

Nitroglycerin (NG) is a vasodilator and has been associated with acute episodes of angina pectoris, myocardial infraction, and sudden death. Workers engaged in the production or use of dynamite are potentially exposed to mixed vapors of nitroglycerin (NG) and ethylene glycol dinitrate (EGDN). Initial exposure to NG (or NG:EGDN mixtures) characteristically results in an intense throbbing headache that begins in the forehead and moves to the occipital region. Volunteers developed mild headaches when exposed to NG:EGDN vapor at concentrations of 0.5mg/m^3 for 25 minutes. It has been suggested that at least some workers may develop headaches at concentrations in excess of 0.1 mg/m^3. Other signs and symptoms associated with initial exposure include dizziness, nausea, palpitations, and decreases in systolic, diastolic, and pulse pressures. These initial signs and symptoms, including headache, are indicative of a shift in blood volume form the central to the peripheral circulatory system, initiated by dilation of the blood vessels.

After 2 to 4 days of repeated NG exposure, tolerance to the vasodilatory activity occurs, probably as a result of compensatory vasoconstriction. Tolerance may be lost during periods without NG exposure, such as weekends and holidays. Chronic repeated exposures to NG and NG mixtures also have been associated with more serious cardiovascular effects, including angina pectoris and sudden death.

Signs and symptoms of ischemic heart disease were observed in nine munitions workers involved in handling a nitroglycerin-cellulose mixture. Within 1 to 4 years of initial exposure, these workers developed nonexertional chest pain, which was relieved either by therapeutic nitroglycerin or by returning to work after the weekend. Coronary angiography performed in five of the patients showed no obstructive lesions. In one patient, observed while in a withdrawal state, coronary artery spasm was demonstrated and readily reversed by sublingual nitroglycerin.

Sudden deaths in previously healthy workers have been reported among those exposed to NG or to NG: EGDN mixtures. Like the attacks of angina pectoris, sudden deaths occurred most frequently during brief periods away from work, in particular on Sunday nights or Monday mornings. In most cases, there were no premonitory signs or symptoms although some subjects had anginal episodes during brief periods away from work. Atherosclerotic plaques, with or without thrombosis, have been found in the coronary arteries of workers at autopsy, but their coronary arteries generally were not occluded to the same extent as those of unexposed workers who had died suddenly.

The pathogenesis of the sudden death syndrome has been postulated to be due to withdrawal of coronary vasodilators (e.g. NG), resulting in vasoconstriction with acute hypertension, or with myocardial ischemia in workers adapted to and dependent on NG to maintain a minimum level of coronary flow. A second contributing mechanism for coronary artery toxicity due to NG may relate to so-called aging of the vessels due to repeated dilation. Other theories suggest that sudden deaths may be related to peripheral vasodilation consequent to reexposure of NG.

Estimates of exposure levels associated with sudden death have not been made because workers typically absorb considerable amounts of NG through the skin in addition to inhalation.

Employees handling NG should be given personal protective equipment to prevent the absorption of NG through the skin. However, neither natural rubber nor synthetic rubber gloves, including neoprene gloves, are impervious to NG. The wearing of such gloves tends to hold the chemical in contact with the skin, thus promoting its absorption. Preferably, cotton-lining gloves should be worn underneath nitrile gloves and both gloves changed ever 2-1/2 hours (USAEHA Technical Guide 24).

More recent studies have suggested that the effects of long-term workplace exposure to NG may not be completely reversed after exposure is terminated. Former workers may be at increased risk for cardiovascular mortality for months to years after exposure has ceased.

Individuals with preexisting ischemic heart disease should not be assigned to work where significant exposure to NG may occur. Early identification of cardiovascular disease is the primary goal of medical surveillance of nitroglycerin workers. A preplacement examination must be administered to all new employees occupational histories, a physical examination, and indicated laboratory tests, record of their pulse rates. Periodic examinations should be conducted semiannually, with the same focus as the preplacement examination. During the periodic examination, the physician should be aware that headaches that occur during work shifts could indicate skin absorption of nitroglycerin, even if air concentrations of nitroglycerin are below the PEL. Examinations with similar content are necessary when exposure to nitroglycerin has been terminated, although surveillance should perhaps extend beyond employment, due to the latency of the withdrawal effects. Monitoring should include pulse, blood pressure, CBC, urinalysis, resting EKG and lipid profile.




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Page last modified: 07-07-2011 02:51:07 ZULU