All chemistry knowing individuals can recall from their early chemistry knowledge that Acidic materials dissolve in water to produce a net surplus of hydrogen, H+ ions and basic materials dissolve in water to produce hydroxyl, OH- ions and both these behave as electrically charged species in water. It is the concentration of these ions which determines the strength of an acid or a base. Strong acids produce higher concentrations of H+ than weak acids and vice-versa for bases too. We can generalize and say that: most common acids have a high solubility in water i.e. we can put them in water, dissolve them and generate ions in solution; they are not flammable, although some highly concentrated acids may ignite other materials; acids react with metals, sometimes slowly, to produce flammable and explosive hydrogen gas; acids neutralize bases, in other words, hydrogen ions react with hydroxyl ions to produce water and resultant heat.

For example, Caustic Soda (a base with chemical formula NaOH) will neutralize a spill of hydrochloric acid (HCl) and the overall reaction will would produce considerable heat and fumes. The presence of water is critical to the acid/base concept. One might consider adding water to acids and bases in order to dilute them and hence make them less concentrated and less hazardous. One rule of thumb in the chemical laboratory is “A ?W and not W? A” that is acid is always added to water and never water to acid. Addition of water to concentrated acid, the only way to combine the two in a spill situation, can cause splashing and bubbling of acid. Dilution may also cause the solution to heat up due to heat of dilution which, in turn will reduce the solubility of the acid in water and generate acid fumes. Most of us are familiar with the term pH used to indicate how acidic or basic a solution is.

Solutions with pH between 0 and 6 are acid, pH 7 is neutral and pH 8-14 solutions are basic. pH readings may be taken using litmus paper and observing the colour change. The pH scale as shown is a logarithmic scale that is factors of 10 separate each value. For example, a 1 liter spill of a strong acid (pH=1) would require 10,000 liters of water to be diluted to pH=5. Dilution to neutral pH would require 1,000,000 liters of water (although this wouldn't be necessary as pH=5 would represent a low hazard for skin contact). Addition of water has the added drawback of spreading the spill around. Abrupt addition of neutralizing agents to concentrated acids in a spill situation will cause fuming and boiling. Neutralization is normally done in a laboratory under highly controlled conditions. Consider that some neutralizing agents can be just as hazardous as the original acid. One would have to add just enough neutralizer to do the job, and no more than that as one could pass the endpoint and turn the solution into a strong base. A concentrated Sulphuric acid spill can be neutralized using sodium bicarbonate (baking soda) fairly safely while neutralizing with caustic soda could produce a lot of heat and fumes. Sodium bicarbonate has a lower heat of reaction; however it will cause fierce bubbling due to the production of carbon dioxide gas. Sodium bicarbonate is not a particularly hazardous material and an excess may be added without concern.

Crushed limestone is also an excellent choice; however the heat of reaction will be higher and hence greater fuming. Neutralization of a large quantity of acid at the site would require the presence of personnel very familiar with this procedure. It is recommended that recovery of as much spilled material as possible should be done prior to neutralization. Clearly there are several chemical properties attributable to acids in general. The release of acid fumes due to neutralization or dilution seems to be the gravest concern. In the case of hydrocyanic acid for example, release of hydrogen cyanide could be fatal.