An employee, 49, of a paint manufacturing company spent eight days in intensive care on life support and has been left with all-over body scarring, partial blindness to one eye, hearing damage, and damage to a knee and shoulder. He was off work for 16 months. The explosion at the company’s premises on August 4, 2020, also caused significant damage to the building. The employee was making paint in a large mixing vessel, which involved the use of flammable liquids. As he emptied resin pellets from a large bulk bag into the vessel, an electrostatic spark was generated, igniting flammable vapor within the vessel, and causing the large explosion. The Health and Safety Executive (HSE) investigation identified that the company failed to implement sufficient measures to control the risk. This included a failure to use a correctly working extraction system to remove the flammable vapors and effective bonding of the bulk bag to prevent the build-up of electrostatic charge that led to the static spark discharging. The company pleaded guilty to breaching Section 2(1) of the Health and Safety at Work etc. Act 1974 and was fined £800,000 with £14,032 costs at Newcastle upon Tyne Magistrates’ Court on November 30, 2022.
We have worked with many flammable liquid processes to design the safety systems intended to prevent this very accident. Years ago, a study showed that the #1 cause of flammable liquid flash fires in processing was the addition of solids to a mixing vessel and that the #1 ignition source for these events was static electricity. NFPA 77, Chapter 13 specifically covers the hazard of “Adding Solids” (13.5). We have two (2) options, although we design to both methods.
1) controlling the static generation and providing a path to ground for it
2) inerting the vessel atmosphere to below the MOC of the flammable atm
NFPA 77 WARNING! Even where the vessel is inerted, large additions of solids will introduce air into the vessel while expelling flammable vapor from the vessel.
This accident appears to be caused by the addition of solids into the mixing vessel. NFPA 77 suggests the following when we are analyzing the hazards associated with such a common task.
- Manual addition of solids through an open port/manway must be done only in 25 kg/55-pound batches. Batch additions larger than 25 kg/55-pounds [e.g., from flexible intermediate bulk containers must be done through an INTERMEDIATE HOPPER WITH A ROTARY VALVE or an equivalent arrangement. The hopper can be inerted separately to reduce air entrainment into the mixing vessel. At the same time, the introduction of flammable vapor into the operating area can be avoided by venting the vessel to a “safe location.” (NOTE: see my other articles defining “safe location”)
- When the addition of solids, even when the solids are noncombustible, is from NONCONDUCTIVE PLASTIC BAGS, the bags must be constructed of paper, plies of paper and plastic in which the nonconductive plastic film is covered by paper on BOTH SIDES, or antistatic plastic. Because grounding clips can be impractical, such bags can be effectively grounded by contact with a grounded conductive vessel or skin contact with a grounded operator.
- Fiber drums or packages should NOT have a loose plastic liner that can leave the package and behave like a plastic bag. All metal chimes on the drum/packaging should be grounded.
- Personnel in the vicinity of openings of vessels that contain flammable liquids MUST BE GROUNDED, and special attention should be paid to housekeeping because the accumulation of nonconductive residues on the floor or on items such as grounding clips can impair electrical continuity to ground.
If your business does flammable liquid processing, NFPA 77 is a MUST-have RAGAGEP!