From Halopedia, the Halo wiki
The Type-3 Incendiary Grenade is a multi-purposed infantry explosives munition, and can be thrown 10 meters by the average soldier. The filling contains pyrophoric alkali metal Caesium chemical compound, a stable yet hazardous chemical compound that was developed by the Jiralhanae. Upon impact with a hard surface, the casing converts to liquid form, burning at around 2200 °C (3992 °F), and causing significant damage to vehicles and infantry alike, automatically killing all nearby infantry in a 4.7 meter (15.5 foot) radius. The stable caesium mixture filler also escapes from the burning casing, splashing over nearby objects and causing significant damage as it burns for 4.5 seconds. The Jiralhanae have, however, employed variants that burn for longer. The flame emitted by the grenade is so intense, it is potentially hazardous to a human retina.
The toxic nature of caesium renders human flesh inedible to Jiralhanae.
The Type-3 Incendiary Grenade was first developed by the Jiralhanae on their homeworld, Doisac. The Sacred Promissory took over the grenade's development and production and started manufacturing several months prior to the breaking of the Covenant Empire.
The grenade was one of many pieces of equipment detailed in Machines, Materiel and Munitions from the Human-Covenant Conflict, 2525 - Present.
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