The radius of the burst is approximately 6 meters, but fragments of the plastic body occasionally fly as far as 27 meters. Effective portions of the agent may be carried as far as 75 to 100 meters downwind. Personnel using these grenades should wear protective gas masks.
Incendiary Grenades
The AN-M14 incendiary (thermite) hand grenade is cylindrical in shape and has a sheet metal body with emission holes in the top (fig. 12-4). It weighs 32 ounces and contains a filler of 26.5 ounces of TH3 thermite mixture. It uses an igniting fuze that sets fire to the thermite filler after the normal delay. The thermite filler bums for approximately 40 seconds at a temperature of about 4300°F. A portion of the thermite filler changes into molten iron that flows out of the grenade and produces intense heat over a small area. This molten iron ignites or fuzes whatever it touches. It is used to ignite combustible materials and to destroy all types of equipment. It burns through about one-fourth inch of steel and welds together steel or iron machinery parts when molten iron flows between them.
I don't know where you got this data from, but a thermite grenade does not do this.
You DO not have to wear a protective mask and it does not burst or carry agents as you stated.
Your quote from the Seabee combat handbook creates a small confusion. The AN-M14 incendiary (thermite) hand grenade is NOT a bursting grenade as suggested by the first paragraph you posted. The AN-M14 only produces a localized very high intensity heat source and molten iron. Thermite is NOT an explosive.
The confusion in what you posted arises from the way your source laid out that page of their manual. The first paragraph you posted was actually the last paragraph of the preceding sub-chapter entitled "Chemical grenades" (tear gas). They mistakenly interposed the graphic of the AN-M14 thermite grenade one paragraph too soon in their page layout.
Your second paragraph is precisely on point and an accurate description of the operation of the AN-M14. Hope this clears up the confusion.
Regards,
Boot Hill