Attempt to index nil with "FindFirstChild" any solutions?

Notes ~ this is inside StarterPlayerScripts, which has an Integer Value named "Air", this is a local script inside of "Air"

Hey all, so I'm trying to make a game where you have a set amount of oxygen and when you run out it starts to damage you. So I made the first part work

local player = game.Players.LocalPlayer -- getting the player
local air = script.Parent -- the IntValue

while wait(1) do -- every one second
    if air.Value > 0 then -- check if any air is remaining
        air.Value = air.Value - 1 -- subtract an air
        print(air.Value.." air remaining.") -- print the air remaining
end

However, when I made some modifications to the script (see below), it stopped working and gave me this error

Players.v1rtical.PlayerScripts.Air.LocalScript:3: attempt to index nil with 'FindFirstChild'

Here is the new (broken) script

local player = game.Players.LocalPlayer
local air = script.Parent
local humanoid = player.Character:FindFirstChild("Humanoid")

while wait(1) do
    if air.Value > 0 then
        air.Value = air.Value - 1
        print(air.Value.." air remaining.")
    else
        print("No air remaining!")
        humanoid.Health = humanoid.Health - 10
    end
end

Hope someone can help, thanks!!