Tuesday, 1 August 2023

‘Curious’ worker ignites foam, causes huge warehouse fire in China

‘Curious’ worker ignites foam, causes huge warehouse fire in China

South China Morning Post on Youtube has the story.

A warehouse storing EPE foam burst into flames after a worker ignited highly flammable foam rolls with a lighter in southern China’s Guangdong province.

Expanded polyethylene is an interesting product.

(Polyethylene foam) Expanded polyethylene (aka EPE foam) refers to foams made from polyethylene. Typically it is made from expanded pellets ('EPE bead') made with use of a blowing agent, followed by expansion into a mold in a steam chest - the process is similar to that used to make expanded polystyrene foam.

EPE foams are low density, semi-rigid, closed cell foam that are generally somewhere in stiffness/compliance between Expanded polystyrene and Polyurethane. Production of EPE foams is similar to that of expanded polystyrene, but starting with PE beads. Typical densities are 29 to 120 kg/m3 (49 to 202 lb/cu yd) with the lower figure being common. Densities as low as 14 kg/m3 (24 lb/cu yd) can be produced.

Base polymer for EPE foams range from Low-density polyethylene (LDPE) to High-density polyethylene (HDPE).

Expanded polyethylene copolymers (EPC) are also known - such as 50:50 (weight) materials with polystyrene. Though other properties are intermediate between the two bases, toughness for the copolymer exceeds either, with good tensile and puncture resistance. It is particularly applicable for re-usable products.

EPE foams were first manufactured in the 1970s.

Production of the PE beads is usually by extrusion, followed by chopping, producing a 'pellet'. Autoclave expansion is the most common route the bead foam. Butane or pentane is often used as a blowing agent (before 1992 CFCs may have been used). Depending on the specific process uses the beads may be cross-linked either by electron beam irradiation (see Electron beam processing), or by the addition of a chemical agent such as Dicumyl peroxide.

How easily does butane ignite? The Effects of Butane Exposure are interesting. Butane is highly flammable and can ignite easily through static electricity, open flames, or other ignition sources. As a combustible gas, butane concentrations anywhere between 1.6% and 8.4% can provide an explosive mixture with air.

An alternate route (JSP Process) to the beads uses carbon dioxide as a blowing agent which is impregnated into the pellets in an autoclave at a temperature close to the plastic's crystalline melting point. The pellets are foamed by "flashing" into the (lower pressure) atmosphere to expand.

Finally molding is done by steam chest compression molding; usually the low pressure variant of the process is used, though the high pressure variant may be used for HDPE based EPE foams.

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