Requirement of Fire Rated Volume Damper and Non return Damper in Car park Smoke Ventilation Ductwork

[Buildtech2]

In car park ventilation system, there are 2 main supply fans connected in parallel through duct work. Both fans are duty fans as per our authority requirements. If any fan fails, there may be possibility back flow of air from another fan. if NRDs are not provided, whole car park ventilation strategy affected. Consultant has provided NRDs in main extract ventilation duct work to avoid back flow but there is no NRD in the main supply ventilation fans duct work.
As per our project specifications, all components of duct work need to be 120 minutes fire rated. We normally do not get fire rated VCDs and NRDs to meet our specifications requirement. Appreciate, if anybody can share their similar experience to overcome this situation.