Standard gas water heaters are one of the most dangerous appliances I see in homes. This one was found in the basement of an extremely leaky house. The water heater has obviously had a hard time venting safely. The corrosion and rust is a sign to look for. All water heaters should be able to draft safely, even under worse-case depressurization. Hiring a BPI Analyst to inspect and test your house is the first step you should take if you have concerns about combustion safety.
For more information on energy audits, follow the link.