Not so safe, but it all depends where you live in the city and all that. Downtown / midtown is the best, anything else is hit or miss. Areas on Moross St. by Grosse point are just as nice as anywhere else. Also, even though Detroit is arguably the most dangerous city in the country, suburbs are very safe.
Air conditioning tonnage has nothing to do with weight. A ton, as used in the HVAC field, is a term that describes how much heat the AC unit can remove from a home in one hour. The measurement for heat is the British thermal unit (BTU). One ton of air conditioning can remove 12,000 BTUs of air per hour. A four ton unit can move 48, 000 BTUs and so on. Therefore, the more tonnage an AC unit is rated at, the more air it can cool.
HVAC is an abbreviation for Heating, Ventilation and Air Conditioning. HVAC systems are the main mechanical infrastructure of a building and provide climate control functions. An HVAC system can range from a compact unit placed in a window sill to a multisystem unit that is installed on a roof or in a basement. HVAC systems are typically the most costly elements of construction.