The Gruntleigh Infant Expo was dramatically disrupted earlier today after a product demo for an experimental BebeSnooz sleep sack took a calamitous turn.

The nocturnal paraphernalia had generated more buzz than a trapped wasp ahead of the expo, toting a record-breaking thermal resistance rating of 10.8 gigatogs.

BebeSnooz Warmthologists were demonstrating the the high tech slumber garment with a Wistar Rat when disaster struck.

As the test rodent was placed in the sack, its body heat was retained at levels “pushing the limits of thermodynamics”, according to early incident reports, and onlookers were powerless to assist when the helpless animal combusted within a few seconds of entering the sleep sack.

As the Warmthologists attempted to unzip the clasps of the sleep sack, the device began to glow a dark shade of crimson – witnesses describe a harsh hissing as it started to burn a hole through the linoleum floor of the expo centre – physicists speculate that the rat had vaporised within the sleep sack and formed a superhot plasma not disimilar to the surface of the Sun.

Hysteria erupted among the audience and dozens received minor injuries as gormless event stewards struggled to coordinate an orderly exfiltration.

The Bebesnooz Warmthologists declared a Level 8 Heat Incident and local Gold Command disaster managers were called to assume control of the site.

The sleep sack had now sunk deep into a well of molten linoleum and scree of unknown depth, and the decision was made to encase the expo centre in a kilometre-wide concrete sarcophagus to prevent damage to the surrounding area from the expulsion of highly acrid smoke.

The borough of Gruntleigh has been evacuated as a precautionary measure, and Cobra is considering a wider evacutation of The Midlands. BebeSnooz shares have risen by 23% in the wake of the incident.