You can reduce some poison gas by spreading chemical compound into the air near the farmhouse.
Mix the correct chemical mix and spread it around the farmhouse.
Unlike normal walkthroughs, in Nice Game Hints you can select just the puzzle you want hints for. Here are listed the puzzles for "Remove some gas with chemistry" in Don't Escape: 4 Days to Survive. The guide you choose only contains information about that puzzle, reducing possible spoilers for other puzzles.