Breakdown for air is about 2000V/mm, so each inch of spark is roughly 50,000 volts (varies somewhat with humidity and atmospheric pressure). You can get Corona discharge long before you see sparks or flashover if the E field is high enough. St. Elmo's fire is a Corona discharge.
It isn't all that hard to develop 40Kv of static, however the energy involved is tiny without a storage device like a leyden jar. Absent the large Capacitor unless the material to be ignited is about the 'flash' point, it won't be ignited. A Piezo Electric igniter converts a fair chunk of mechanical energy into Electrical Energy. IT isn't an electrostatic discharge. Getting Zapped by one hurts a lot more than an electrostatic charge because there is a lot more energy involved, and the flash point for methane, butane and propane is well below room temperature, so these devices are quite effective for lighting burners on gas stoves, BBQ's and butane lighters.
The chances of generating enough energy via static electricity from walking around to burn carpets, or melt.burn plastic or anything except exceptionally flamable chemicals is just about zero. If it wasn't people would be routinely be killed by such discharges. Only takes about 1 joule (1 watt-second) applied in the right place and at the right time cause a fatal heart arhythmias. Most ESD involves orders of magnitude less than 1 joule. It takes an ESD the size of a lightning strike to kill someone!
However it is pretty easy to have sufficient static charge on your body to punch right through the gate on an MOS device, destroying it. A microscopic hole in the insulated gate kills an MOS device. Microjoules will do it easily.
Many devices are protected by Zener diodes, and usually you have to work on them on a grounded worked area, wearing a grounding strap on your wrist. The Insulation on the gate is so thin that it only takes a few hundred volts to punch a hole in it!
Most consumer electronics rated for 20kv ESD at the customer interface (control panel buttons/switches), but often much less elsewhere (battery compartment, viewfinder etc)...