Gasmasks only slow down the absorbing of radiation into the body effecting major organs but radiation still effects you. Its not a gas leak but a radiation leak.
https://mega.co.nz/#!t0ATBZzL!50Jo6L...-QTESydwk6o7_k download this, then put the files from this archive into your DeadZ folder. Then launch your launcher and you should be ok.
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