From Lexicanum

Blind grenades are a more complex version of a smoke grenade, releasing dense smoke as well as infra-red bafflers and broad spectrum electro-magnetic radiation to disrupt enemy scanners. The broad range of interference makes most forms of direct attack through it impossible. The cloud can quickly dissipate given the correct weather conditions.¹

Sources

• ¹:Warhammer 40,000: Wargear (2nd Edition)