Now, FFG aren't exactly known for their flawless and exhaustive rules systems, but this is a little much even for them. According to page 137 of Into the Storm, most ships carry "huge reserves", but a single 200 liter barrel would produce a blast of over one and a half kilometer in diameter, and likely do over 1000 damage (enough to rip through a couple of dozen 36 armour bulkheads - a couple of barrels exploding would logically tear a voidship in half). Why do I need orbital bombardment when I can just drop barrels of this stuff on the enemy and achieve roughly the same effect?

Note that even if your GM isn't the sort to give you stuff for free just because it *should* be on your ship (I personally don't), Promethium is still Abundant, and so can be easily acquired in vast quantities.

Hell, even a lowly armsman can do the Imperium a great service as a suicide bomber, rushing enemies with 36kg of the stuff for a lovely 144 metre blast - longer than the range of many ranged weapons, and doing easily enough damage that enemies can be killed through walls and most other sorts of cover.

So, I'm curious. How do you guys deal with this sort of thing? For the sake of dicussion, we're assuming that players are taking basic steps to prevent the plan from backfiring - not standing closer than 144 metres away from their suicide bombers, dropping the barrels from lighters that they can afford to lose, operated by people they can afford to lose, from high enough that autocannons and such can't reach etc.

Questions of crew morale are made moot by mind control and basic efforts to maintain secrecy, or at the very worst inflammatory speeches by someone with Charm in the 130-area.

Personally, I went with the route of less resistance and outright banned Promethium and similar items. Between demolition packs and meltabombs, I find there's enough explosives in the game. So, what about everyone else? Gentlemen's agreements with your players? House rules? Sudden genestealer attack?

I usually go with the Gentleman's Agreement. I am fully aware that there are logistical measures to be put in place for acquiring and resupplying a ship with Promethium and other such supplies and so I don't worry about it. Likewise there are Halo Barges and Guncutters on their ship, and as long as my players don't get too fancy with this, I let this gentle, invisible system continue to work as needed with a promise that I won't sabotage it.

If they start trying to weaponize these components, which they are free to do, I have made it clear that I would then expect them to track exactly how much Promethium is on their vessel, where they're storing it, what precautions they're taking against sabotage, how they're resupplying it, how much they're going to use for a given period of space travel, and how they make sure that the totally reputable buyers they're purchasing from on Footfall aren't just giving them tainted Promethium that might spontaneously explode as part of an ongoing sabotage by a rival Rogue Trader against their vessel.

Gentlemanly like.

Or just remember your the GM and its your rules and you don't have to stick with what's in the book.

Personally I'd allow my players to come up with an interesting plan that used a barrel or two of promethium to get them out a tight spot or enabled them to blow up some enemy behind cover. However I wouldn't let it be anywhere near as effective as orbital bombardment or a genuine explosive or anywhere near comparable mass. Remember 1 shell from your macrobatteries is at least the size of an average house (and possible much larger) and packed with far more than 200 l of high explosive.

As has been said, if I recall correctly, your normal ship weapons causes blasts of over a kilometer in diameter. There's no reason to dump promethium on them.

Also, I'm unclear where you're getting your math from. If I remember right, promethium isn't particularly explosive- it just burns well. It's fantasy napalm, not gasoline.

I've always loved the fact that 40K uses promethium as a liquid fuel source, considering that it is a radioactive metal that melts at around 1000 degrees C. Now I do realize it is supposed to be this pseudo Greek word for gasoline, but I still find it funny.

Don't worry, they also use depleted deuterium as the hyper-dense penetrators of bolt shells. Let me remind you that deuterium a) cannot be depleted because it is a stable atom and b) is hydrogen, the lightest atom.

Let me remind you that deuterium cannot be depleted

YET. Life always finds a way.

I've always loved the fact that 40K uses promethium as a liquid fuel source, considering that it is a radioactive metal that melts at around 1000 degrees C. Now I do realize it is supposed to be this pseudo Greek word for gasoline, but I still find it funny.

It's named for Prometheus, who stole fire from the gods. It's a flammable chemical, but whether it's gasoline is questionable.

Took this from Lexicanum so might not be the most Fluff-iest source but what can you do. (My image of this stuff is Oil)

Promethium is a general term for any form of fuel in the Imperium.

The term also commonly refers to the substance used as fuel for Imperial flamer weapons, a highly volatile incendiary gel which immediately ignites on contact with oxygen.

It reaches super hot temperatures. Similar to napalm, the gel sticks to an individual, continuing to burn on its own accord, even underwater and in space. It also fuels most spacecraft and vehicles, both military and civilian.

In addition to this, Promethium is used to create an array of everyday necessities, ranging from dyes and plastics to pharmaceuticals and synthetic protein bars.

Promethium is extracted and refined in a number of different ways. Some of the most common methods are extracting it from the atmospheres of gas giants, the mining of ancient organic material deposits, and the processing of certain rare ices that are only found on ice worlds.

Yep. Looks like petroleum and various petrol products to me.