Not enough information is provided to answer the question. Putting certain materials in certain ducts with demonstrating a compliant reason to the Mechanical or Building inspector is a violation of the IBC or IMC. The MEP or Fire Protection Engineer needs to work this out.
"Maybe the sprinkler pipe was there before the duct work and conduit????"
Yes, I have seen this (or something quite similar) and recently. The sprinkler line was run in a warehouse and the duct work was installed later and it crossed the sprinkler line right beneath a sprinkler causing an obstruction. The fault would lie not with the mechanical contractor who installed the ducting, but with the engineer of record who didn't catch it.
Regards
D
A thing moderately good is not so good as it ought to be
Thomas Paine