I believe Zero is correct. Somewhere I have the notes to prove it. A few years ago this type of helmet was showing up on eBay often described as either a Baltic or Russian artillery helmet, but after some research I found someone who demonstrated it was actually a Russian fire helmet. If I can locate the info I will post it here (not being a firehelmet collector I have been a bit casual with it!). Anyway, I strongly support Zero.
Russian fireman, prewar.
See here Пожарная охрана планеты Земля and here Hot-lids | Eastern Europe & Russia . The ones that seem to show up for sale are the basic shells, the combs, chinstraps, badges, all gone if they were ever there in the first place.
(Still haven't found the info I referred to above - must improve my piling system.)
Thanks to everyone for your help. I've finally been able to identify it as a Russian fire/civil defense helmet. It's actually quoted as being one of the most rare helmets ever produced by the USSR. It's included in a book, and I'm attaching a link to it below. If anyone is interested, I'll be posting it on ebay within a week. Thanks again! Russian Helmets, by Clawson, rare civil defense
I am reluctant to suggest that the renowned Robert Clawson is wrong, but it does strike me that this helmet is really an economy version of a comparatively widely used Russian fire-service type (see the fire-helmet webpages I cited previously). Possibly not that rare either; in my picture files I have at least two instances copied from eBay within the last few years (one had been labelled 'Finnish experimental', the another as 'unknown possibly Russian' by the original sellers). It's not actually featured in Clawson's RUSSIAN HELMETS; the webpage is a collection of addenda, really.
However, an interesting and unusual helmet, nothing detracts from that!
Cool, good to know for future