i am working on a tropical flower farm in central queensland growing
mainly heliconias and we are having trouble getting the required shelf
life from a variety called fire flash , i am told by a freind that
used to work on a farm many years ago that they used a chemical inthe
water to extend the shelf life but he cannot remember the name of the
chemical can you help ?

Glycerine (glycerol)? I know it has been used to preserve flowers...

Sorry; I may be wrong... Here are a coupple of links that might help
you a little:

Sugar and Acidity in Preservative Solutions for Field-Grown Cut
Flowers:
http://www.umass.edu/umext/programs/agro/floriculture/floral_facts/presvcut.html

Heliconia sp.:
http://aesop.rutgers.edu/~greenmachine/COMM_FL_DESIGN/CUT_FLOWERANDGREENSID/CUTFLOWERS/CUTFLOWERPAGES/HELICONIA.HTML

Try recutting the stems underwater to prevent an air-block in the
xylem tubes of the stem.  Also, virtually anything dissolved in the
water will assist since it will reduce osmotic loss from the flower. 
Sugar is a good bet.  The glycerol idea is good too.