cables in dry riser shaft

Not exactly catching the situation you describe. Usually dry or wet risers are in firefighting shafts or protected stairs. If I get you correctly, this is a multi story building with the dry riser in a cupboard in the protected stairs or fire fighting shaft? That cupboard has been pirated by parties who have used it as an electrical services riser. The dry riser is a facility for firefighters, who may use the landing on which the dry riser is located as a bridgehead to fight a fire on that storey level or above, or in some cases, below. That being the case, the cupboard door needs to be open to access the valve. The last thing firefighters need is a passage for smoke to spill into the bridgehead landing via the cable routes, enclosed or otherwise.

A call to the local fire chief is likely to result in a direction to remove the offending cables altogether. 

Not exactly catching the situation you describe. Usually dry or wet risers are in firefighting shafts or protected stairs. If I get you correctly, this is a multi story building with the dry riser in a cupboard in the protected stairs or fire fighting shaft? That cupboard has been pirated by parties who have used it as an electrical services riser. The dry riser is a facility for firefighters, who may use the landing on which the dry riser is located as a bridgehead to fight a fire on that storey level or above, or in some cases, below. That being the case, the cupboard door needs to be open to access the valve. The last thing firefighters need is a passage for smoke to spill into the bridgehead landing via the cable routes, enclosed or otherwise.

A call to the local fire chief is likely to result in a direction to remove the offending cables altogether.