In the second shot of Davis looking down from the Window where he is to shoot the Explosives, Westerbrook is seen at the base of the Paul Revere statue yelling at the crowd but you cant hear him. This is before Westerbook actually walks thru the crowd to the Revere Statue where he starts yelling Fire.
When Jack Davis is unloading the plastic explosive he slowly and gently removes the lump of explosive material from the wooden crate. This precaution is unnecessary. One of the characteristics of plastic explosive is that it's very stable and insensitive to most physical shocks. C-4 cannot be detonated by a gunshot or by dropping it onto a hard surface. It does not explode when set on fire or exposed to microwave radiation. Detonation can only be initiated by a shock wave such as when a detonator, inserted into the material, is fired. Indeed, Jack Davis' plan to detonate the bomb by firing into it with a rifle is not an effective method of detonation and everyone is perfectly safe. That said, common sense says you don't dance in a mine field and it's likely that the manufacturer recommends against such actions.
John Westerbrook's last name is spelled incorrectly as Westbrook on the official board outside the meeting hall.