151. i^Iithin and close to the firebarl, everything will evaporate or melt. Atsome distance froro the explosion the tvo nxost important effects of thermar-radiation will be to cause burns ("flash burns") on exposed skin and to ignitefi.res. second-degree burns to unprotected. skin n4y occur 3 km, from the explosion.al:d at 2 kn, third-degree burns ld1l be frequent. (Second-<legree burns cau-sepai.n and blisters. Third-degree burns, wheie parts of the skin are destroyed,cause disfiguring scars cal"led cheloids. ) At less than z km., thernal radiationcafl be expected to kil1 most people directr-y exposed to it. ldaterials that areeasily ignited' such as thin fabrics, paper or dry leaves, nay catch fire atmore than 2 kn. from ground-zero. rhis rnay cause numerous fires" which undersome conditions nay form a huge fire storm enveloping nuch of the target area andad.d.ing nuraerous further casualties. That was the case in Hiroshima, at_though itis considered. less 1ikeIy in modern cities.
**Analysis**
The text appears to be discussing the effects of a nuclear explosion on human health and the environment, specifically the immediate and short-term consequences of thermal radiation on people and materials. The text highlights the severity of the burns and the potential for widespread fires, which suggests a strong connection to the category of Health.

**Category**
Health