How do I protect from Blast damage?

Moving forward with my rockets, Here is where I am at right now.

ball = script.Parent
damage = 100

function onTouched(hit)


    local humanoid = hit.Parent:findFirstChild("Humanoid")
    if humanoid~=nil then
        tagHumanoid(humanoid)
        humanoid.Health = humanoid.Health - damage
        wait(0.00000001)
        untagHumanoid(humanoid)
        connection:disconnect()
    else
        damage = damage / 2
        if damage < 2 then
            connection:disconnect()
            ball.Parent = nil
        end
    end

    if math.random(1,1) == 1 then
        explosion = Instance.new("Explosion")
        explosion.BlastRadius = 2
        explosion.BlastPressure = 500000
        explosion.Position = script.Parent.Position
        explosion.Parent = game.Workspace
        connection:disconnect()
        ball.Parent = nil
        cancollide = true
    end

end

function tagHumanoid(humanoid)
    -- todo: make tag expire
    local tag = ball:findFirstChild("creator")
    if tag ~= nil then
        local new_tag = tag:clone()
        new_tag.Parent = humanoid
    end
end


function untagHumanoid(humanoid)
    if humanoid ~= nil then
        local tag = humanoid:findFirstChild("creator")
        if tag ~= nil then
            tag.Parent = nil
        end
    end
end

connection = ball.Touched:connect(onTouched)

r = game:service("RunService")
t, s = r.Stepped:wait()
d = t + 5.0 - s
while t < d do
    t = r.Stepped:wait()
end

ball.Parent = nil

What I want is if the rocket hits a wall or something I can specify rather than any object (like the baseplate), How do I make it so it only damages what it contacts rather than the humanoid behind cover? (not looking for a Jointbreaker)