Harmless when diluted, rocket fuel when potent

Hydrogen peroxide, the chemical that the German police say two terrorism suspects planned to use to make bombs, is a simple molecule — two oxygen atoms and two hydrogen atoms — with myriad uses. The hydrogen peroxide available in drugstores is just 3 percent hydrogen peroxide by weight; the other 97 per cent is water. Such highly dilute solutions are used to bleach hair and disinfect wounds. But at greater concentrations, above 70 percent, hydrogen peroxide can be used as a rocket propellent, or as an ingredient for explosives.

The suspects arrested in Germany on Tuesday had obtained 1,500 pounds of moderately concentrated solution, made up of 35 per cent hydrogen peroxide. That concentration is potent enough to make at least one type of explosive. If the hydrogen peroxide were mixed with acetone — the primary ingredient of most nail polish removers — the resulting chemical reactions could generate significant amounts of the explosive triacetone triperoxide, or TATP. TATP has been used by Palestinian suicide bombers and is believed to have been the explosive in the attacks in London tube in 2005.