in propellants. nitroglycerin is an oily liquid that may explode when subjected to heat, shock, or flame. alfred nobel developed the use of nitroglycerin as a blasting explosive by mixing nitroglycerin with inert absorbents, particularly "kieselgur", or diatomaceous earth. he named this explosive dynamite and patented it in 1867. it was supplied ready for use in the form of sticks, individually wrapped in greased waterproof paper. dynamite and similar explosives were widely adopted for civil engineering tasks, such as in drilling highway and railroad tunnels, for mining, for clearing farmland of stumps, in quarrying, and in demolition work. likewise, military engineers have used dynamite for construction and demolition work. nitroglycerin was also used as an ingredient in military propellants for use in firearms. nitroglycerin has been used in conjunction with hydraulic fracturing, a process used to recover oil and gas from shale formations. the technique involves displacing and detonating nitroglycerin in natural or hydraulically induced fracture systems, or displacing and detonating nitroglycerin in hydraulically induced fractures followed by wellbore shots using pelletized tnt. nitroglycerin has an advantage over some other high explosives that on detonation it produces practically no visible smoke. therefore, it is useful as an ingredient in the formulation of various kinds of smokeless powder. its sensitivity has limited the usefulness of nitroglycerin as a military explosive, and less sensitive explosives such as tnt, rdx, and hmx have largely replaced it in munitions. it remains important in military engineering, and combat engineers still use dynamite. alfred nobel then developed ballistite, by combining nitroglycerin and guncotton. he patented it in 1887. ballistite was adopted by a number of european governments, as a military propellant. italy was the first to adopt it. the british government and the commonwealth governments adopted cordite instead, which had been developed by sir frederick abel and sir james dewar of the united kingdom in 1889. the original cordite mk i consisted of 58% nitroglycerin, 37% guncotton, and 5.0% petroleum jelly. ballistite and cordite were both manufactured in the form of "cords". smokeless powders were originally developed using nitrocellulose as the sole explosive ingredient. therefore, they were known as single-base propellants. a range of smokeless powders that contains both nitrocellulose and nitroglycerin, known as double-base propellants, were also developed. smokeless powders were originally supplied only for military use, but they were also soon developed for civilian use and were quickly adopted for sports. some are known as sporting powders. triple-base propellants contain nitrocellulose, nitroglycerin, and nitroguanidine, but are reserved mainly for extremely high-caliber ammunition rounds such as those used in tank cannons and naval artillery. blasting gelatin, also known as gelignite, was invented by nobel in 1875, using nitroglycerin, wood pulp, and sodium or potassium nitrate. this was an early, low-cost, flexible explosive. medical use main article: medical use of nitroglycerin nitroglycerin belongs to a group of drugs called nitrates, which includes many other nitrates like isosorbide dinitrate (isordil) and isosorbide mononitrate (imdur, ismo, monoket). these agents all exert their effect by being converted to nitric oxide in the body by mitochondrial aldehyde dehydrogenase (aldh2), and nitric oxide is a potent natural vasodilator. nitroglycerin in three different forms: intravenous, sublingual spray, and the nitroglycerin patch. in medicine, nitroglycerin is probably most commonly prescribed for angina pectoris, a painful symptom of ischemic heart disease caused by inadequate flow of blood and oxygen to the heart and as a potent antihypertensive agent. nitroglycerin corrects the imbalance between the flow of oxygen and blood to the heart and the heart’s energy demand. there are plenty of formulations on the market at different doses. at low doses, nitroglycerin dilates veins more than arteries, thereby reducing preload (volume of blood in the heart after filling); this is thought to be its primary mechanism of action. by decreasing preload, the heart has less blood to pump, which decreases oxygen requirement since the heart does not have to work as hard. additionally, having a smaller preload reduces the ventricular transmural pressure (pressure exerted on the walls of the heart), which decreases the compression of heart arteries to allow more blood to flow through the heart. at higher doses, it also dilates arteries, thereby reducing afterload (decreasing the pressure against which the heart must pump). an improved ratio of myocardial oxygen demand to supply leads to the following therapeutic effects during episodes of angina pectoris: subsiding of chest pain, decrease of blood pressure, increase of heart rate, and orthostatic hypotension. patients experiencing angina when doing certain physical activities can often prevent symptoms by taking nitroglycerin 5 to 10 minutes before the activity. overdoses may generate methemoglobinemia. nitroglycerin is available in tablets, ointment, solution for intravenous use, transdermal patches, or sprays administered sublingually. some forms of nitroglycerin last much longer in the body than others. nitroglycerin as well as the onset and duration of action of each form is different. the sublingual or tablet spray of nitroglycerin has a two minute onset and twenty five minute duration of action. the oral formulation of nitroglycerin has a thirty five minute onset and a duration of action of 4-8 hours. the transdermal patch has an onset of thirty minutes and a duration of action of ten to twelve hours. continuous exposure to nitrates has been shown to cause the body to stop responding normally to this medicine. experts recommend that the patches be removed at night, allowing the body a few hours to restore its responsiveness to nitrates. shorter-acting preparations of nitroglycerin can be used several times a day with less risk of developing tolerance. nitroglycerin was first used by william murrell to treat angina attacks in 1878, with the discovery published that same year. industrial exposure infrequent exposure to high doses of nitroglycerin can cause severe headaches known as "ng head" or "bang head". these headaches can be severe enough to incapacitate some people; however, humans develop a tolerance to and dependence on nitroglycerin after long-term exposure. although rare, withdrawal can be fatal. withdrawal symptoms include chest pain and other heart problems. these symptoms may be relieved with re-exposure to nitroglycerin or other suitable organic nitrates. for workers in nitroglycerin (ntg) manufacturing facilities, the effects of withdrawal sometimes include "sunday heart attacks" in those experiencing regular nitroglycerin exposure in the workplace, leading to the development of tolerance for the venodilating effects. over the weekend, the workers lose the tolerance, and when they are re-exposed on monday, the drastic vasodilation produces a fast heart rate, dizziness, and a headache. this is referred to as "monday disease." people can be exposed to nitroglycerin in the workplace by breathing it in, skin absorption, swallowing it, or eye contact. the occupational safety and health administration has set the legal limit (permissible exposure limit) for nitroglycerin exposure in the workplace as 0.2 ppm (2 mg/m3) skin exposure over an 8-hour workday. the national institute for occupational safety and health has set a recommended exposure limit of 0.1 mg/m3 skin exposure over an 8-hour workday. at levels of 75 mg/m3, nitroglycerin is immediately dangerous to life and health.