Perchloric Acid Explosion
Thursday, January 25, 2018
A person following a literature prep, was heating in an Erlenmeyer flask a dilute water solution of a roughly 0.700 g of organic compound with about 1 mL of 70% perchloric acid. Over time all the acidic solution evaporated, leaving behind perchlorate salts which are shock and heat sensitive explosives. Because it was left unattended, there was an explosion in the hood soon afterwards. The ceramic of the hot plate had shattered and was irreparably damaged. No irreparable damage to the Schlenk line was caused possibly because of the shape of the filtration flask which caused the explosion to be lateral or horizontal.
There was one person near that hood but not in direct path, and they suffered from ringing in the ear and immediately left. DEHS was immediately informed, and they performed the perchlorate test in the hood the next day, which came out negative because all perchlorate salt had exploded.
Precautions that were taken before the incident:
Fume hood sash was lowered. PPE was on. The sashes of the hood were down and partially closed so they got chipped. This was the essential safety component that prevented the person nearby from getting any physical injury.
NEVER heat perchloric acid even in diluted solutions. Perchloric Acid can become unstable and cause fires or explosions under three different conditions:
1) Contact of hot perchloric acid (heat makes it a powerful oxidizer) with organic material, results in fires or explosions.
2) Formation of the extremely unstable anhydrous (> 85%) perchloric acid
3) Formation of unstable perchlorates (heavy metal and organic perchlorates).
If a procedure calls for heating, concentrating or using metal with perchloric acid look for an alternative. Other non-coordinating anions could be considered. In this case the protocol was modified to use hexafluorophosphoric acid HPF6 instead of heating perchloric acid.
Also do Not leave perchloric acid throughout the process and keep other people in the area informed.
Again NEVER heat perchloric acid even in diluted solutions
Additional Resources
Perchlorate salts, their uses and alternatives
Wayne C. Wolsey
J. Chem. Educ., 1973, 50 (6), p A335
DOI: 10.1021/ed050pA335
Publication Date: June 1973
Safe handling of the perchloric acid in the laboratory
Lowell A. Muse
J. Chem. Educ., 1972, 49 (9), p A463
DOI: 10.1021/ed049pA463
Perchlorate safety: Reconciling inorganic and organic guidelines
J.R.Long
JCHAS