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Aerosol Laboratory Safety - Eliminate Potential Ignition Sources

By: John Chadwick
Tel: (603) 895-0778
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I have been wandering around the aerosol industry for the last 40(ish) years and the last 20 as a technical consultant. Various consulting projects provided me the opportunity to visit many aerosol laboratories and production facilities.  Today I would like to discuss - and perhaps rant a bit - about aerosol laboratory safety.  While the attention to safety issues has dramatically improved over time, I am still amazed how often the simplest safety precautions are sometimes overlooked when filling aerosols sample with flammable propellants. I’ll save my horror stories for another article, except for one particularly relevant example.

Let’s start with a test, of sorts. Don’t worry it’s just pass/fail (yes/no) and focuses on the elimination of potential ignition sources in your lab. These are just a few of the routine questions I ask during a aerosol laboratory safety audit… 

  • Are aerosol cans grounded during filling, spraying, and puncturing (depressurizing) for disposal?  In case you are wondering… yes, a static electrical charge has enough energy to act as an ignition source. 

  • Are the lab technicians grounded by standing on grounded anti-fatigue mats during propellant charging? This is especially important in dry cool environments (especially during the winter season).

  • Is a grounding wire attached to the aerosol cans you are degassing for disposal?

  • Are your single station propellant filling burettes and semi-automated propellant fillers grounded?   

  • Is the filling of flammable propellants being done in a dedicated explosion proof (XP) hood? If your answer is “yes” you may want to make sure. I have seen “XP” benchtop fume hoods used to charge flammable propellants where: the hood motor and/or the hood lights and/or the electrical socket on the hood cabinet are not XP rated.  This is a “fail” as all three must be XP rated for the hood to be safely used for aerosol filling.

  • If you are using a bench top hood, is there a flammable gas detection sensor mounted at or near floor level below the opening window of the hood?  Is it calibrated frequently? Flammable hydrocarbon propellants, along with being odorless and colorless, are heavier than air – thus the floor level sensor. If there is a leak, or a rupture in a flammable propellant transfer line in the hood, and the flow of propellant overcomes the capacity of the hood’s air flow to vent the gas, then the excess propellant will pool unnoticed on the floor area spreading outward and upward throughout the room. Following is the horror story example I mentioned…

In the late 1980’s I was working for a large aerosol CPG self-manufacturing company when there was an accident in one of the company’s quality control labs.  A large quantity of aerosols was being de-gassed for disposal in an XP rated hood. Two technicians were unloading cases of aerosols and puncturing (degassing) them in a hood. While the hood was XP rated, there were no gas detection systems in the room. It was late and there were many cases of product remaining to be punctured, degassed, and emptied for disposal. To move through the cans more rapidly, the technicians began degassing dozens of cans simultaneously in the hood.  Unfortunately, the amount of propellant being released exceeded the hood’s extraction capacity and accumulated unnoticed. Remember, hydrocarbon propellants are colorless, and odorless. At some point after the LEL (lower explosion level) for the propellant/air mixture in the room was exceeded.  A third person entered the area and turned on a (non-XP) light switch at the door to light another part of the room. As he flipped the switch, the spark generated as the contacts inside the switch closed ignited the flammable atmosphere and the room exploded. I was based in another location, but I knew the two technicians standing in front of the hood. The third person, who turned on the light switch, was blown back out of the room and survived his injuries, the two technicians at the hood were not as fortunate.

All too often we become complacent, equipment may not properly maintained, and procedural shortcuts are taken to get the work done faster. A familiar mantra: “We’ve been doing it this way for XX years without a problem”. My response: “that’s great, until you have a problem.”

Now, let me put this in perspective. The catastrophe I described above is very rare. However, when working with flammable propellants, it is the POTENTIAL for this level of danger which drives the various safety aspects of equipping and operating an aerosol laboratory (and full scale production facilities as well).    

Aerosol sample filling capability has numerous rewards. Among them; rapid turnaround of test samples for development purposes, small scale production of samples for product stability testing, production of sales samples, new product exploration, product spray optimization, etc., etc.  AND, to be clear, filling pressurized, flammable aerosols is a HAZARDOUS OPERATION and requires specialized equipment, safety systems, procedures, and training, all of which have come a very long way since the accident I described.

Final quiz question - are your safety systems and procedures up to date?  Before you answer, let me share with you one of my favorite quotes which I find especially useful when aerosol safety is involved, and that is: “Trust but verify”.   

The phrase “Trust but verify” was made famous by Ronald Reagan in December 1987 after the signing of the INF Treaty with Mikhail Gorbachev (elimination of specific nuclear weapons).


John Chadwick, Principal at Aerosol Technical Solutions, LLC, is a veteran in the aerosol industry. Mr. Chadwick has a proven track record of successfully participating as an expert witness in court cases involving aerosol products and/or aerosol technology. His expert witness services include aerosol product failure analysis, reports, deposition, and testimony as needed. In addition to participating in product liability cases, Mr. Chadwick has also provided expert witness services in matters of intellectual property disputes and technology licensing agreements.

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