This video is about as picture-perfect as we can get to show us how static is an ignition source. The plastic rolls (commonly called expandable polystyrene or EPS for short is made with Pentane, a highly flammable CAT 1 gas that is heavier than air and has a Minimum Ignition Energy of just 0.22 mJ. When this EPS is made, it must be allowed to “off-gas” for a period of time, as the pentane is still being liberated well after it is made. Our friends across the pond at the HSE Executive put out a really nice HSE Information Sheet on this risk (Fire and explosion risks from pentane in expandable polystyrene (EPS). As we can see, the worker who had been crawling around on the rolls inside the box truck was exiting the truck when he stepped off a roll and as soon as his foot came into contact (most likely even before contact) we see the ignition of the flammable gas.
NOTE: we do not know how long the worker or the rolls were inside the truck before the incident