How extensive was the effect of the hail and fire?
Revelation 8:7 (ESV)
7The first angel blew his trumpet, and there followed hail and fire, mixed with blood, and these were thrown upon the earth. And a third of the earth was burned up, and a third of the trees were burned up, and all green grass was burned up.
The reference to a third indicates considerable severity (see commentary on Rev 8:6). Though not all people die from this plague, all are certainly greatly distressed.
7 The first angel blew his trumpet, and there followed hail and fire, mixed with blood, and these were thrown upon the earth. And a third of the earth was burned up, and a third of the trees were burned up, and all green grass was burned up.