Aluminum is relatively soft, and as temperature increases, expands more than the metals from which connectors are made. When current flows through a connection, the connection becomes warmer. The expansion of the aluminum, confined under a screw terminal, generates tremendous pressure, so that the metal “flows” into the empty spaces in the connector. When the electrical load is removed, the aluminum cools and contracts, and a gap forms between the wire and the connector. The slightly loose-fitting connection now has a higher resistance, and more corrosion forms in the gap, further increasing the resistance. The next time a heavy load is applied, the connection becomes even hotter, and so on, until one day the connection may burn out, or surrounding material may ignite.
its safe as long as you use De-Ox Electrical Grease on all connections.
Aluminum building wire was commonly used in the 1960s and 1970s as a less expensive alternative to copper. The wiring itself, if proper over current and short circuit protection is maintained, should provide the owner with a lifetime of service. The problem as mentioned in other posts is the connections. I have not seen too many failures here in Colorado caused by terminations but that is where it will happen. If there is a concern I always recommend replacing the devices and outlets with al/cu rated devices or pigtail the terminations with copper wire. Both options installed per the UL Listings by a qualified electrician.