Part 2: Tales of a Faulty Fume Hood: the hidden bomb

 
The saga continues...

Hey folks, thank you for making Part 1 of this saga a phenomenal one. It garnered the highest hits so far so I'm blowing your Tuesday blues away with another sequel from a true to life experience.

A midsummer nightmare

It was summer, the air was dry and the heat was scorchingly high. Everyone was in frenzy to finish their scheduled tasks. I was in a separate room, alone with five fume hoods. I was doing acid digestion, looking after my test samples, making sure it doesn't get burned.

Then a tile (literally a floor tile) from the rear wall of the hood fell off and went straight to the top of the hotplate. I've observed some tiny sparkles. But never did I knew that it was the beginning of something bad. It caught fire and went horribly big in a few seconds. Like a firework, it consumed whatever fuel that was inside.

I was terribly shocked and muted. Pictures of the whole building burning down plays on my mind. I felt horrible, responsible. I tried to put off the fire but it only went angrier, more ravaging in strength. I hurriedly unplugged the outlet and went away to seek help. I heard people screaming, ballistic. I heard the fire alarm ringing, painfully reminding me that there's a fire going on.

The whole building burning down plays again on my mind. Like it was the most inevitable reality. Then rescue came. The fire was out but not the fear that I felt inside.


The hidden danger
It was a lesson well learned. We put up an investigation team to identify the culprit. Theories were formed, some were pointless. There was one that says maybe I was just clumsy. I was blamed. It was hypocritical of me to stay silent. I spoke up for the story that needs to be told.

After further investigation, the findings were conclusive. All along, we were silently building up a bomb inside our fume hood that readily awaits to be detonated. Our lab is heavy on the consumption of perchloric acid. In a day, we can consume more than half a litter of this acid to digest our samples. But we were clueless that slowly by slowly, perchlorate salts were deposited on the internal lining of the fume hood and on the ducting system. It was just bidding its time and waiting for an opportunity to be ignited. Unfortunately, the inevitable happened.

The silent bomb: explained
Perchloric acid is a powerful oxidizing, strong acid useful for certain analytical procedures, but carries potential dangers due to the formation of perchlorate salts within the fume hood, ductwork, and fan components. When heated, perchloric acid vaporizes, then condenses to form metallic perchlorates. Its salts are extremely shock sensitive which can explode with very little disturbance.

The salt by-products easily deposits on grouts, which in our case, on the sides of the tiles. Our fume hood's interior were made of several tiles so imagine how conducive it was towards the formation of these explosive salts.

The solution
Ours was a typical example of a misuse of fume hood. What we had in our lab was designed for general purpose only. However, it was heavily used for excessive heating of acids including perchloric acid. Some parts were also decaying due to exposure to corrosive acids. 

This kind of analysis demands a specialized fume hood with a wash down system to help prevent the formation of perchloric salts and eliminate the risk of explosion. Every after analysis, you just turn on the wash down system and it will simply wash-off any salts that were built-up on the sides of the hood. I spoke with an engineer from Esco Micro and they said the interior design should also be seamless, without any gaps or joints, as to eliminate any potential site for deposition. They have a specialized fume hood for this kind of analysis and they simply call it the Perchloric Acid Fume hood.

So next time you design your laboratory, learn from our mistakes and avoid repeating the same ugly experience. Lucky for me the fire never went off the trail but you may never know how worst it can get next time.