While CNG may be safer for the environment than gasoline, is it really safe to have an HRA installed in your home? It's really no different than living with other natural gas home appliances, such as a hot water heater or clothes dryer. Phill is designed with a built-in sensor that shuts the system down if it detects a malfunction such as a methane leak or improper connection. Professional installation should comply with any applicable building codes and regulations, including venting indoor units to the outside.
In a study produced by the National Renewable Energy Laboratory (NREL), it was found that although new owners were most likely to (intentionally or unintentionally) misuse their HRA in the first year of installation, the overall use of the appliance is safe: You're 10 times more likely to be struck by lightning than to experience a safety incident resulting from normal use of Phill [source: National Renewable Energy Laboratory].
In addition to safety concerns, infrastructure is also a problem for HRAs. CNG is generally transported through a network of natural gas pipeline, not by truck or rail. Distribution infrastructure -- whether or not fuel is available where you live -- plays a big role in whether or not NGVs are successful. Even if consumers want cleaner cars, if they don't have easy access to fuel they won't bring one home. And even if you live where there is proper infrastructure in place, some natural gas suppliers place restrictions on installations -- so although it's a step toward greener transportation, be sure to do your homework before bringing Phill home.