why is it necessary for the halflife of the radioactive material in the smoke detector to be very long?
it goes back to the first fire box alarm systems the first person to spot a fire would open the box and pull the lever to sound the alarm and the nearest station would respond if on arrival the firemen needed more equipment they would pull the lever again this would call in help from the next nearest station a 3 alarm fire would call the off duty men from the near by stations back on duty and they would also respond to the fire a 4 alarm fire would be a general alert for all available units in the city to respond to the fire. so with each alarm that sounded the number of fireman called on to respond increased. it used to end at four alarms. but with the changes to technology the number of people and units that could be brought in has increased, though they don't ring bells anymore they have kept the terminology. a 9 alarm fire is a disaster call for help from anyone who can send help. Military, other states, etc.
PVC is not rated for drinking and cooking with. However, CPVC (Notice the extra C in there) IS rated for drinking and cooking with. Copper is the best because it has anti-microbial properties. Copper is bad for microbes. That's why hospitals are using paint that is copper based. I have PEX plumbing. It's rated for drinking and cooking, AND it's easy to install. Flexible, so you can bend around corners rather than have to glue in an elbow. And anywhere you DO need a fitting, they can be brass fittings with copper compression rings to hold them in place. I actually re-plumbed my whole house in one day using PEX. There WERE a few tricky spots, but over all, it's a big improvement over what they had originally.