Flash Fire in chemical intermediate products while drying
Company XYZ has various stages to produce #ABC finished product. One of those stages is transferring the intermediate product after filtration to a vacuum tray dryer. At this point, the material is called “FGH cake.”
The procedures describe the steps as follow
1. They start filtering the #FGH material from the reactor to the filtration equipment. The #FGH intermediate product after filtration contains powder and solvent. It is important to mention that the solvent used during the reaction was toluene that is a non-conductive liquid.
2. The #FGH cake is transferred from the filtration equipment to static dissipation plastic bags manually (by utilizing a stainless-steel scoop).
3. Once, the amount specified in the SOP is in the bag; the operator proceeds to zip it.
4. At the time of the incident, the operator put eleven bags in the vacuum tray dryer’s room.
5. The operator put the one the bags on the stainless-steel table, that has four rubber wheels on the bottom.
6. He opened the bag.
7. He grabbed the scoop to transfer the #FGH material to the trays of the dryer.
8. He performed this step four times, and suddenly the flash fire occurred.
The XYZ company created a team to investigate the root causes to prevent the re-occurrence of this incident.
The team found the following:
The primary reason was static electricity that acted as a source of energy to complete the fire triangle: toluene vapors (fuel), static (source of energy) and oxygen.
The causal factors that contribute to the incident were:
1. As part of the company’s cGMP and safety policy, the operator shall wear the following PPE:
a. Coverall (85% polyester, 15% cotton).
b. Latex gloves instead for ESD medical material gloves.
c. The stainless-steel table and scoop were not grounded and bonded.
d. There was no evidence of the ESD certification of the plastic bags. It was a mere supposition by management.
e. By procedure, the operator was wearing ESD safety shoes. However, the floor was not ESD, nor the operator could test the shoes neither.
f. The company XYZ never conducted the PHA; therefore, the team had concerns about fire code compliance.
Several intermediate products at this stage are hybrid mixtures. In this case, there are two aspects to consider: At the beginning, the criteria which prevail is to find it as a flammable liquid due to the amount of liquid as part of the cake after filtration. The data to get that will be critical to design and operate the dryer is:
• Minimum Ignition Energy.
• Autoignition Temperature.
• Low Explosion Limit.
2. During the drying process, the cake becomes a powder that could be combustible; therefore, the following data is paramount according to NFPA 654 “Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids.”
• Go/no test to determine combustibility, if it is:
o Minimum Ignition Energy,
o Limit Oxygen Concentration.
o Decay Charge. It is critical to determine relaxation time to dissipate the static after drying.
o Autoignition Temperature.
o Minimum Ignition Temperature.
In Canada, each provincial has its fire code. These codes have the NFPA 86 “Standards for Ovens and Furnaces” as a reference.
In this case, the company XYZ, conducted the process hazard analysis, and they found the following to improve:
1. Lack of Oxygen concentration measurement or lack of LEL measurement during the drying process. The company installed an Oxygen sensor.
2. The company XYZ made the decision to make the atmosphere inert before starting the operation.
3. Engineering reviewed the thickness of the dryer’s wall to verify the necessity explosion proof panel. In this case, the dryer was complying, if not, the NFPA 68 “Standard for Explosion Protection by Deflagration Venting” would apply.
4. Engineering examined the vacuum system to test if it is not carrying dust into the system.
5. Maintenance checked the grounding system of the dryer per NFPA 77 “Recommended Practice for Static Electricity.”
6. Per NFPA 30 “Standard of Flammable and Combustible Liquids” that specifies that the floor shall be static dissipation for this type of operation. At the moment of the incident, the floor was covered by an epoxy coat. They changed to ESD floor.
7. Currently, XYZ company is compiling all the data state above for all its intermediate and finish products.
8. Engineering checked the electrical system of the equipment and room to be in compliance with the provincial electrical code, which makes reference to NFPA 70” National Electrical Code.” Some components were in accordance, others not, therefore every component is Ex approved.
9. The safety department replaced all coveralls and gloves for ESD approved. Because of GMPs, the coveralls and gloves need to be disposable to avoid cross contamination, the reason why the FR clothes do not apply in this case.
10. Engineering installed an ESD shoe tester, and they looked for a certified ESD bag.
Disclaimer: The information contained in this case study is to be used only as a case study example for teaching purposes. The information in the case study is both factual and fictional. Opinions formulated by the author are intended to stimulate class discussion.