1. A heating element comprising: an exothermic composition having an oxidizable metal, a carbon component and water, wherein the heating element comprises tribasic alkali metal phosphate, wherein the water content of the heating element is equal to or greater than 50 parts by weight and equal to or less than 90 parts by weight per 100 parts by weight of oxidizable metal, and wherein the content of tribasic alkali metal phosphate, expressed in terms of the amount of phosphate group, is equal to or greater than 0.5 parts by weight and equal to or less. less than 1.1 parts by weight per 100 parts by weight of oxidizable metalla.2. Heating element according to Claim. 1, wherein the heating element further comprises one or two or more electrolyte (s) selected from a sulfate or chloride of an alkali metal or alkaline earth metal, ferrous chloride and ferric chloride zheleza.3. Heating element according to claim. 2, wherein the electrolyte is one or two or more selected from sodium chloride, potassium chloride, calcium chloride and magniya.4 chloride. Heating element according to claim. 2, wherein the heating element comprises potassium ion and sodium ion, and wherein the weight ratio (W / (W + W)) content of the potassium ion (W) in the heating element to the sum (W + W) content of potassium ion (W) and the content of sodium ion (W) in the heater element is equal to or higher than 0.1 and equal to or lower than 0,6.5. Heating element according to claim. 4, further comprising zagustitel.6. Heating element according to claim. 5, wherein the thickener is a mixture of one, two or more agent (s) selected from thickeners based polysaccharide thickeners, starch-based thickeners based on cellulose derivative, thickeners1. Нагревательный элемент, содержащий: экзотермическую композицию, имеющую окисляемый металл, углеродный компонент и воду,причем нагревательный элемент содержит трехосновный фосфат щелочного металла,причем содержание воды в нагревательном элементе равно или больше
