Thanks for the question.
Shower grenades may be used during the first mission.
Zombie rules will be included in the game rules emailed out a week before the event in the game packet. Here's a brief summary.
All players may walk quickly (zombies and humans). As this is a night game with large amounts of CQB, running is not allowed.
Zombies can only be killed by chest or back shots. Headshots are not allowed for safety. Although these do occur, so it is highly recommended that players wear mouth or face protection.
Zombies infect by attacking a human and getting two hands on to any part of the players body (arms, legs, torso.) Guns don't count as part of a human.
Zombies are encouraged to act like them. They are not allowed to behave like normal humans or move tactically.
MTT has used these rules at two previous zombie events and about 10 small games. Almost all the players felt these rules worked well for both the humans and zombies.