Continuing in a series of strange things that I have seen while consulting at hospitals…
Some organizations fail to install sprinklers underneath the ductwork that is 48-inches wide or wider. This facility did not forget, but the sprinkler-fitter who installed this pipe for the sprinkler head attached it to the ductwork, which is not permitted.
The sprinkler pipe can only be suspended from the building itself (i.e. structural beams, joists, etc.), and not from anything else.
There is one exception to that rule… Sprinkler pipe may be suspended from a hanger that also supports ductwork, provided the hanger is designed to support the weight of the duct, the pipe, the water in the pipe, and an additional 250 lbs. (see NFPA 13-2010, 188.8.131.52). If you ever see sprinkler pipe suspended from the same hanger that supports ductwork, ask the installer to provide documentation that the hanger can support that weight.