Dynamically updating 3 validation lists based on the first selected items

[ponyman]

Hi Guys, Can you help! I have a sheet which contains the following headers: Area, Type, Resource and data below:

area_class	resource	resource_type
Packaging	Canning Line 1	process
Packaging	Canning Line 2	process
Packaging	Glass Line 1	process
Packaging	Glass Line 2	process
Intake Bay	Liquid Conc Intake	process
Intake Bay	CT1	tanks
Intake Bay	CT2	tanks
Intake Bay	CT3	tanks
Filtration	Filter1	Process
Filtration	Filter2	Process

In this sheet i have used the formula: =UNIQUE(IF(ISBLANK(Source_Class[area_class]),"",Source_Class[area_class])) in cell: I4 to populate a dynamic list of all areas. The resource_types: =UNIQUE(FILTER(Source_Class[resource_type],Source_Class[area_class]=Dashboard!H5)), and the Resources: =UNIQUE(FILTER(Source_Class[resource],(Source_Class[area_class]=Dashboard!H5)*(Source_Class[resource_type]=Dashboard!H7))). Using a separate worksheet: "Dashboard", the USER selects from the cell H5 the dropdown there required area selection derived from a validation list "=Classes!$I$4#". I can populate the required list of types and resources. Still, the problem is the USER wants to have the cells in the Dashboard automatically changed to the first in the relevant validation lists and not leave incorrect data from previous selections when they make a selection to either Area or Type.
For example, existing selection
Area =Intake Bay (dashboard H5),
Type = Tanks (dashboard H7),
Resource = CT1 (dashboard H9).
When the USER selects "Packaging" in Dashboard "H5", the results of the Type, is incorrectly left with Tanks from the previous selection. As there are no Tanks, associated with the Packaging Area, they want this to default to a valid type item (ie Process), which could then drive a change to the dashboard cell H9 resource to a valid list item.

Do you always need to make a new selection in each dropdown, or is it possible to dynamically change either the type or resources made on the previous selectionS?

I could use a VB to clear the contents of each Dashboard cell, H5,H7 & H9, and force the USER to make a new selection each time, but it would be quicker for these cells to update to the first in their validation list dynamically.

Is this possible, and if so, how could it be done?

Many thanks in advance.