Multiple Order Entry systems and downtime

We have just gone live on a new Emergency Department system and have run into a new issue with downtime – duplicate orders.  All Order Entry runs through our HIS (McKesson SERIES) for order# assignment. Orders can originate in HIS, LAB, Radiology, or Emergency departments – all Order interfaces are bidirectional.  

The problem occurs during downtime – SERIES has 35 minutes of downtime for backups 3 times a week.  Emergency Dept has always sent manual requisitions to LAB during downtimes and continue to do so now that they have their own Order Entry system, but they also want to enter the LAB orders into their new ED system.  Does anyone else have this problem?

When you have downtime(everyone does at sometime) do you require that LAB be the only source of LAB order entry until all systems are back up?