Brother INTELLIFAX 820MC - Manual (Page 9)

Never install telephone wiring during a lightning storm.
Never install telephone jacks in wet locations unless the jack is specifically designed
for wet locations.
Never touch uninsulated telephone wires or terminals unless the telephone line has
been disconnected at the network interface.
Use caution when installing or modifying telephone lines.
Avoid using a telephone (other than a cordless type) during an electrical storm. There
may be a remote risk of electric shock from lightning.
Do not use the telephone to report a gas leak in the vicinity of the leak.