Two researches were working at the laboratory when the apparatus they were using exploded, sending glass fragments into their face and upper body. The researchers conducted solvent extraction by the Soxhlet Extractor apparatus for fat determination.  As one researcher did not wear the safety glasses, the explosion was also sending glass fragments towards his eyes and caused eye injuries. Lab personnel helped them and called for emergency. They were taken to the hospital by the ambulance and received treatment for their injuries.

What they are doing? Curde fat determination – Soxhlet Extraction

Crude fat content is determined by extracting fat from the sample using solvent (e.g. diethyl ether), then determining the weight of the fat recovered. It is a lengthy process as the solvent extraction step requiring up to a day. The sample is contained in a porous thimble that allows the solvent to completely cover the sample. The thimble is contained in an extraction apparatus that enables the solvent to be recycled over and over again. This extends the contact time to dissolve all of the fat contained in the sample.

What was the cause of the explosion?

The cause of the accident is still investigated by relevant authorities in Taiwan. However most likely, the explosion was caused by peroxide contaminants in the solvents that had concentrated to the level that being unstable during the extraction process. Diethyl ether was used in the extraction and it forms peroxides over time. The extraction process concentrated the peroxides in the bottom of the round bottom flask and along the glass vessel of the apparatus. Then any movement of the apparatus could cause the dry and shock sensitive peroxides crystal to explode.

Diethyl ether is highly volatile and has a low flash point and a low explosive limit by volume in air. Therefore another cause of the accident may be the flammable vapors escape from the extraction apparatus. If the extraction apparatus is not placed in a properly function chemical fume hood and there are open flames or sparks present in the laboratory, a fire or ever an explosion may be happened.

How can the accident be prevented?

The laboratory users should become familiar with peroxide forming chemicals by reading its material safety data sheet and preparing a safe operating procedure. And following steps should be taken to minimize the risk from using peroxide forming chemicals.

1. Purchase small quantities and try to completely use materials so that remaining peroxide forming solvent is not left in the container. Large container stored long period increases the chance of forming peroxides. Also the lab users should purchase solvent with stabilizer added to reduce the rate of peroxide formation.
2. Peroxide forming chemicals should be stored away from air and light. It should be stored in the original container which usually is dark colored or metal cans, with a tight fitting cap.
3. Always date containers of peroxide forming chemicals with the date received and date opened, as peroxides are formed by an auto-oxidation process, their concentration builds up with time. After a container is opened, peroxide test should be done periodically, it should be also labeled with the test date and re-test date. Do not use old containers of peroxide forming chemicals or containers undated without testing.
4. If you notice a viscous liquid or crystalline solids in the peroxide forming chemicals, stop using it immediately and get assistance from HSEO. It is possible these crystals may be shock, friction or impact sensitive and could explode.
5. Always wear proper personal protective equipment in the laboratory. Lab users should wear safety glasses which protect their eyes from the exploded glass fragments and chemicals.
6. For any experiment setup using highly flammable solvent, it should be conducted in the well-ventilated chemical fume hood to prevent flammable vapor accumulate. Also the fume hood sash also protects the lab user from potentially explosive chemicals.