Tinker With Blur by using a script?

You could use tweenservice but it would be better if you use repeat

local Part = script.Parent -- put the script under a parent
local Blur = game:GetService('Lighting'):WaitForChild('BlurEffect') -- So put the blur inside lighting

Debounce = true

function Fade()
    repeat
        wait(0.01)
        Blur.Size = Blur.Size + 0.1
    until Blur.Size >= 50

    wait(2)

    repeat
        wait(0.01)
        Blur.Size = Blur.Size - 0.1
    until Blur.Size <= 0
end

Part.Touched:connect(function(hit)
    if Debounce then
        Debounce = false

        if hit.Parent:FindFirstChild('Humanoid') then
            Fade()
        end

        Debounce = true
    end
end)

If you have any questions about this script please ask me, if you want it so the blur is client only you should connect it to an event, good luck!