is there any rules about breaking objects? like the enemy's weapon or a generator?

I can't remember if there's anything official (besides Power Fields for weapons) on damaging objects, but within my gaming group, we tend to allow attacking objects, treating the cover they would provide as their wounds, with no critical wounds.

Therefore, directly attacking an Armaplas door would result in you having to inflict 32 damage through it's soak to bring it down.

It *is* pretty odd that there isn't a rule that details building structure by virtue of thickness, or building crits, or something like that. At what point is the ferrocrete cover you are utilizing simply destroyed by the incoming plasma? Tough adjudication.

I think a decent house ruling is to assign structure equivalent to the armor rating of any given piece of cover, and allow any damage that beats the AP to damage both the structure and any guardsman behind it. If the structure begins to take crits, it can simply lose a percentage of AP relative to the critical damage until it no longer provides AP. This also means that if a righteous fury occurs on a covered location, that cover will lose some protective value.

See Final Testament's Scutum Pattern Bunker for a starting point.

I believe DH core had a sidebar buried somewhere in the combat section that listed the armor value of various materials, such as plasteel, plascrete, rockcrete, iron, wood, etc. Top end of the scale was plasteel at AV 32, IIRC.

It was nearly impossible to find the sidebar table on purpose, though. I only found it by accident.

page 199 of Dark Heresy, 1st Edition, lower right corner

Cover

Cover is a vital part of surviving a firefight and a good Acolyte knows that you go for your cover first and then draw your gun. There are no penalties to Ballistic Skill Tests made to attack targets standing partly behind cover. However, there is a chance that the shot may hit the cover rather than the target. It is up to the player to decide which parts of his body he is exposing when behind cover. Unless the Acolyte is attempting a rather crude form of psychological warfare, as a rule of thumb, a character firing around or over cover will have his body and legs concealed. If the shot would hit a body location

that is concealed behind cover, work out the Damage against the Armour Points of the cover instead, with any excess being applied to the target as normal (see Table 7-10: Cover Types for a guide to the Armour Points of different kinds of cover).

Damaging Cover

Cover is not invulnerable. Attacks can Damage or destroy the protection afforded by cover. Each successful hit against cover that deals Damage in excess of the Armour Points it provides will reduce the cover’s Armour Points by 1. For example, a bolter shot that penetrates a light wooden door would reduce the door’s AP to 3.

Table 7-10: Cover Types

Cover Type AP

Light Wood, Armour-glas, Light Metal 4

Heavy Wood, Flakboard, Sandbags, Ice 8

Rockcrete, Thick Iron, Stone 16

Plasteel, Armaplas 32

The same is on page 253 of Only War Core

Still, only rules on cover - nothing really on objects other than the aforementioned power field

Yeah ... it's a major failing in the rules. No question about it.

If you are interested in blowing stuff up, field manual 5-250 (explosives and demolitions) may be worth looking at. If you need to supply your PCs with enough explosives to do the job, look up the thing you need blown up in the field manual and see how much explosives it would take. Which would generally be much more than most game masters would want to let you have. But blowing up stuff can take 'a lot' of explosives.

For example, if you want to blow a ~ 2 meter diameter hole in a 'good concrete' wall, and you don't have time to do things like tamp earth on top of your explosives before setting them off, you'd place the expolsivers against the wall, around 1 meter off the ground and blast.

you'd need around 20 pounds (~8.8 kg) of TNT. Assuming the 1kg demolition charges in the game are as effective as TNT, you'd only need 9 of them to get the job done.