Fire while cleaning glassware

Title

Friday, April 8, 2016

Situation

At approximately 4:30 PM, a researcher was cleaning glassware used for anionic polymerization and purification of monomers. All pyrophoric chemicals used in the reactions had been quenched four days ago and the flasks had been left open to air following the quench. The glassware was being cleaned with tetrahydrofuran, dilute hydrochloric acid, and distilled water. The cleaning agents were first poured into a 2 L beaker before being poured into the waste bottle. When the beaker was about half full, the THF vapors in the beaker caught fire. The fire was promptly put out using the nearby fire extinguisher. Nobody was hurt and there was no damage to the hood or any equipment within. There were no sources of heat or flame near the beaker and all pyrophorics used had been quenched four days prior to the cleaning. The researcher is not sure what may have caused the incident.

Suggestions

Extreme care should be taken whenever dealing with pyrophoric agents. NEVER add water to hetergenous mixtures, which held pyrophorics. All of the possible causes sound like they didn't happen, and individually seem rather unlikely, however it was probably an unconscious combination of several of them.

Possible causes:

Unexpected reactive material composition

Additional glassware from other experiments with reactive contaminants was also cleaned.
The enthalpy of solvation of HCl heated the solution sufficiently to ignite THF vapors. Possible if the HCl was labeled incorrectly and not actually dilute.
Other incompatible bottles in the vicinity were unconsciously used.
Peroxides were in the THF either from being distilled or very old in which case the inhibitor would have been used up.
Pyrophorics were coated in an oil layer or oxide coating that prevented effective quenching and exposure to air. Then when the outer layer was removed by cleaning and the pyrophoric residue ignited while rinsed into THF vapors, igniting them.

Unexpected ignition source

Dry lab conditions caused a spark which ignited the THF.
Electrical device nearby (hot place, outlet etc) caused a spark which ignited the vapors.
Cleaning agents were used in an order that allowed a difference in conductivity between the rising vapors and liquids falling through the vapors to cause static ignition.

Things that went well

Quenched pyrophorics before leaving.
Work performed in a hood.
Researcher knew how to extinguish a fire.

Cleaning agents were rinsed into a beaker instead of straight into the waste container.

Had the cleaning rinses been put directly into the waste bottle a larger volume would have been involved. It's possible the flames might not have been seen in a waste bottle and the flaming bottle capped. This could have either put out the fire or caused an explosion. The fire was probably only noticeable because it was in a clear (presumably) beaker instead of the often amber colored waste bottle. Rinsing reactive materials into an intermediate container to verify they are stable before transferring into a waste bottle will help limit the size of any potential problems.

Reminder- Report Fire Extinguisher Use

1. Call 911 to report a fire was extinguished.

2. Request a replacement extinguisher from Facilities Management 4-2900. No charge.

3. Discuss incident with group.