There are probably few smells worse than that of a decomposing rodent. After a rat dies, the body begins to break down, releasing a combination of methane, sulphur dioxide, hydrocarbons and benzene derivatives into the air that creates the unpleasant smell. Sometimes the carcase is difficult to locate, or in an area where it cannot be removed by the homeowner. Even if it is removable, the odour can linger for weeks. However, with a bit of persistence, there are several methods for getting rid of the unpleasant stench.
Find and remove the carcase of the dead rat, as it will continue to smell until it has completely dried out. Use rubber gloves to place the body into a plastic bag, sealing tightly before placing the carcase in the garbage. Scrub or spray the area where the carcase was found with vinegar or bleach.
Drill a hole into the wall approximately 12 inches above the floor, if the carcase is in a wall. Using a spray tip that can moved in all directions, spray the chosen disinfectant, masking solution or odour neutraliser into the hole. Reseal the hole in the wall with the hole filler.
Ventilate the affected area immediately, using one or several fans to force fresh air into the area.
Spray the masking agent or odour neutraliser into the air with a misting or fogging machine, if the rat carcase cannot be located. This will immediately neutralise the odour, but will require repeat applications until the carcase has completely decomposed.
Run an air purifier that uses an absorbent filter with either silica gel or charcoal. As air circles through the filter, it will trap odour-causing particles.
If the rat has died in the wall or ceiling, it might cause a stain or damp spot; it might also be found by looking for flies or maggots in the area of the smell. If you need to drill a hole into the wall to neutralise the dead rat odour, spray the solution on either side of the carcase in the wall for additional odour coverage.
Be cautious about claims for deodorising or ionising devices to remove odours. Ozone generators are a concern to the Environmental Protection Agency, and ionising devices have not been scientifically proven to work on this type of odour.