A Release in the Wrong Department
At 14:34 on 3 November, a plant making semiconductor components in Ansan, south of Seoul, began losing nitric acid. About 150 people were moved out of the building. Six workers were treated for eye irritation, coughing and headache. The fire service sent 16 vehicles and 48 personnel and declared the site secure at 18:57, four and a half hours later. The city told residents to keep windows shut and closed a metro entrance nearby.
Investigators point to how the acid was moved: by forklift. In plants of this kind, nitric acid is not synthesised or reacted on site. It arrives in drums and intermediate bulk containers, is wheeled to a storage room or a cleaning line, and is decanted. The worker closest to a pallet-load of it is often a logistics operator whose footwear was chosen for impact and slip resistance, and whose gloves were chosen for grip.
Concentration Is the Specification
Nitric acid resistant describes a family, not a product. Occupational databases separate the grades sharply. At 10% and 50%, natural rubber, polychloroprene, nitrile, butyl and PVC all hold beyond eight hours at half a millimetre. At 65%, only fluoroelastomer reaches eight hours; polychloroprene, butyl and PVC drop to about two hours, while nitrile and natural rubber are listed as unsuitable. At the fuming grades, only fluoroelastomer is offered at all.
A buyer who orders one acid glove for a dilute cleaning bath and a 68% drum has downgraded the second job without noticing. Film thickness shifts the number too, and data sheets do not always agree with the databases, so tested concentration, thickness and temperature belong in the enquiry rather than the catalogue.
Nitric acid is also an oxidiser before it is an acid. Spilled onto cardboard, pallets or oil it can ignite, and the reaction gives off nitrogen dioxide: brown fumes, more than twice as heavy as air, collecting in pits, sumps and drains. Respiratory protection, not gloves, sets the limit here.
Boots, Runoff and Four Hours
The response ran for four and a half hours. Long before it ended, the floor held neutraliser, acid and wash water, and that is where footwear earns its place. Moulded PVC or butyl boots without laces, eyelets or stitched seams survive repeated washing; deep tread that can be scrubbed keeps residue from travelling into vehicles and homes. Trousers go outside the shaft while decanting, so acid runs off the boot rather than into it.
Then there are the 150 people walking out. Their own shoes are the quickest route for acid out of the building and onto a bus seat. Overboots issued at the exit, in a civilian size run and wearable while standing, cost little and close that route.
What Belongs in the Order
Ask for breakthrough data at the concentration actually stored, to EN 16523-1 or ASTM F739, not a generic acid rating. Fix a change point at decanting and drum handling rather than at the end of a shift. Keep a gauntlet that laps over the sleeve. Reserve thin nitrile for dilute solutions and brief splash. Specify moulded boots, chemical-resistant soles and no metal hardware. Stock overboots across the same size range as gloves; a kit holding three sizes protects almost nobody. And quote shelf life at a stated storage temperature, since a steel cabinet in a warm climate ages elastomer faster than the label suggests.
The Ansan release was not a chemistry failure. It was a logistics task with chemical consequences, and the equipment list had not caught up.