Would that be a Faraday cage then?

Faraday does not apply if the objects in the cage are in contact with the cage, the Faraday principle would only apply if the containers in the cage are on a rubber mat in the cage, I.E rubber wheel of a car Faraday Effect of a motor vehicle. The building is earthed and with the cage in contact with it would also be partially earthed but if there is possibility of it being hit by lightening then I would suggest earthling the cage it self.

The word by the way, is lightning. "Lightening" means making lighter.

messy,
NOOOOOOOOO!
PLEASE DO NOT make random connections to the lightning protction system!
You would divert currents away from their desired destination and could cause serious damage!
We are talking about serious voltages here.
Also and speaking as a qualified electrical engineer and electrical contractor, there are very few who understand lightning systems fully, me being one! As one of the requirements of professionalism is knowing your limits this is why I am not explaining what you should do, but suggesting you get further advice or undertake further investigations.
IF you really want to connect this try Furse for advice or the lightning conductor installers for the building.
What is the expected incidence of lightning?
How high is this cage?
It is metal but is it more of a conductor than those things around it?
Is it higher, this more likely to be struck?
If you earth it will it become a lightning conductor which is not really what you want is it?
I tried to reply earlier but the site is broken on my pc at the moment, all other sites & forums I use are OK, this one don't work!
Must be IOSH getting their own back for my previous comments that were deleted!

Messy,
How do you typically address lightning as an ignition source in FRA, where applicable?

If the cage is at the same height or higher than the existing lightning protection system’s components (strike termination devices), the cage maybe subjected to a direct strike. If the cage mesh is 5 mm dia or more, it can serve as a strike termination device and it can be bonded or grounded into the existing system via a sheathed copper conductor CSA of 50 mm^2 . Not sure, I would want to set the cage up as a strike termination device, given the intended use. Alternately, the cage can be placed under a zone of protection of the strike termination devices.

For my money, I would prefer to locate within an LPZ.

Refer to BS 62305

I am not competent in assessing lightning protection and make that fact known in my FRA findings if appropriate. However, I do assess whether lightning protection has been fitted and whether it's been serviced.

If not, I consider the design, use and height of the premises and it's neighbours, and where appropriate advise the RP to seek further assistance from a competent contractor.

I refer to BS62305, but only insofar as this is a UK accepted benchmark for such protection.

This particular case is slightly different as I think everyone will agree it is unusual to find a cylinder cage in such a location. I have never consider earthing a cyl cage, but due was concerned about the potentially vulnerable position of this one - thus the question on this forum.

The cage cannot be located elsewhere as this premises has no outside space.

Thanks to all for your assistance

Jane,
Maybe you should alert all manufacturers and suppliers of lead covered copper lightning conductors and air terminals to this fact.