Don’t Get Bit, Avoid Piranha Solutions
Traditional Piranha solution is a 3:1 mixture of sulfuric acid (H2SO4) and 30% hydrogen peroxide
(H2O2), used to clean organic residues off substrates. Because the mixture is a strong oxidizer, it will remove most organic matter, and it will also hydroxylate most surfaces (add OH groups), making them extremely hydrophilic (water compatible). Piranha solutions are extremely energetic and have been responsible for a number of serious laboratory accidents. To highlight why we are concerned about piranha solutions please read the following real life story of a Piranha solution explosion:
A group of researchers regularly cleaned their glass sinter funnels by running it through piranha solution them into a vacuum flask. One of the researcher made the mistake of leaving a trace of acetone in the vacuum flask. When the Piranha solution hit the acetone there was a violent explosion. Fortunately they were wearing their protective eye wear which protected their eyes or they would more than likely have been blinded.
The explosion was so forceful that it was heard from two labs away. The first person on the scene found the researcher on the floor halfway across the room surrounded by a large pool of blood. The force of the explosion completely destroyed the flask with the largest fragment found only being about 2 mm even though it had been wrapped in heavy black electrical tape. The metal 3 prong clamp that held the flask had sheared off. A row of glass cabinets along one wall were peppered with holes from the shrapnel.
The researcher had been wearing rubber gloves, a thick sweater, a lab coat, an apron and safety glasses at the time of the explosion. The fume cupboard sash was partially down and absorbed some of the blast preventing the student from catching all of it in the face. The researcher’s arm on the hand that was holding the sinter funnel when the flask exploded received most of the damage. The glove was completely flayed and their arm had several hundred small bits of glass embedded in it as well as several fairly large lacerations. There was some damage to nerves and tendons and a wound was discovered about 20 mm in diameter adjacent to their jugular vein. On top of the blast damage the researcher was also covered with hydrogen peroxide and sulfuric acid; the main ingredients of the piranha solution.
On top of all of this the researcher was working ALONE in the laboratory and was found trying to get up, but not very successfully. Think about the difficulties of stand up in a pool of your own blood and sulfuric acid on a laboratory floor while dazed and injured from an explosion the next time you are pondering working alone while using piranha solution.
Please, if you are thinking about using a piranha solution below are some important points to consider before you begin:
- First and foremost- Do Not Use Piranha solutions. Piranha solutions are extremely energetic and may result in explosions, therefore before using Piranha solution you should try alternative safer methods and only use piranha solutions as a final resort.
- Always use glass (Pyrex® is preferred) containers. The solution can degrade plastic containers causing failure of containment.
- Ensure all containers are properly labeled to identify those containing piranha acid solutions.
- Always mix the solution in a chemical fume hood, utilizing the hood sash as a barrier between you and the solution. Wear appropriate PPE including; acid resistant lab coat and/or apron with sleeve covers, gloves (rubber or butyl) and chemical splash goggles.
- Always add hydrogen peroxide to sulfuric acid while gently stirring. DO NOT add sulfuric acid to hydrogen peroxide.
- The hydrogen peroxide concentration should be kept under 30% and should NEVER exceed 50%.
- Piranha solution will become very hot with temperatures exceeding 100°C during preparation. Handle with care to avoid thermal burns.
- Do not mix piranha solution with incompatible materials such as organic acids, organic solvents, or other organic materials. Do not mix with bases (e.g., Photoresist). Mixing piranha with incompatible materials can lead to an explosion.
- Ensure all containers and substrates are rinsed and dried before coming in contact with piranha solutions. Piranha solution is intended to remove residues only.
- When submerging items in piranha baths, place items in the piranha solution slowly and carefully. The solution needs time to stabilize after each item is added. Apply piranha solution to substrates carefully as well.
- NEVER TIGHTLY CAP piranha solutions. To prevent pressure build up you should use a vented cap.
- After use, always allow piranha solution to react overnight in a labeled, non-sealed container within a fume hood prior to final disposal.
With the above considerations, only use Piranha solutions as a last resort and please take the time to ensure your safety and the safety of others by handling and storing piranha solutions appropriately.