What if the penalty exceeds the players skill?

e.g. A player has BS 40 and gets a -50. Can't he hit at all, just with a 01 or does he still have a 10% chance left?

Couldn't find a rule in the books.

with the errata i think the most you can be negative modified is by -30.

+/- 60 is the modifier cap per DH eratta.

Unless you are using a house rule that allows auto-success and crit-fail on certain rolls then it is quite possible to stack penalties up deep enough to make certain acts mathematically impossible.

I don't personally find extreme situations being impossible to be a bad thing. DH characters can do some pretty **** amazing things, so having an occasional extreme impossibility is probably a good thing to have come up from time to time. Not frequently, mind you, but occasionally. Obviously stupid things should be harder far more often than well thought out actions. A roll of 96+ is always considered a failure in DH so I have heard some players argue that 1-5 should be an auto-success. Nothing wrong if you decide to do this for your game. I can say with certainty that I am NOT adding auto-success rolls as a house rule to my game. Assuming you have a mature enough group to not have to worry about cheating on dice rolls there is still just too much of a "cheese-window" there for my liking. Some things are just plain NOT possible under bad enough circumstances!

Intimidate a pair of orks after displaying brutality and strength? Sure, roll it!

Intimidate 5,000 orks as they charge across a shelled field directly at you and the 4 surviving PDF troopers taking shelter behind a broken Sentinel Scout by using harsh language.... No. Not happening. "But I rolled a 02!" Seriously now....

One idea that is within the spirit of the rules that might help for those BAD situations is a modified use of fate points. I am somewhat flexible here for players that are willing to spend these prescious cookies in dramatic ways that do not violate the spirit of the game. Since one published use for a fate point is to improve the quality of a roll by one margin of success then why not allow a player with an unfortunate pile of combat modifiers to spend a fate point to gain a +10 "fate modifier" (10 being one MOS, so this is essentially a mathematically balanced photonegative of the published use). I once had a player trying to take an opponent alive roll an unfortunately timed Emperor's Fury turn his "bash suspect with a staff" move into a "tear suspect's leg off from blunt force trauma and kill him with massive system shock and blood loss." move. The player immediately asked if he could spend a fate point to LOWER his damage by a D5. The game allows you to increase damage by 1D5, so why not lower it? I allowed this since it was cool and utterly justified.

One other thing to remember: It is not always appropriate, but for characters with suitable skills or appropriate circumstances there is always the "assist another" rule to help offset horrible odds a little. An extra +10 in the right spot can be a real life-saver!

@ZillaPrime Thanks nice post.

Why do you think 96+ is always a failure? Is it in the rules? Not afaik, just the for the gun jams.

@Velvetears it's +/- 60 for Combat Difficulties and +/- 30 for any other roll.

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And i think i'll go for "it's imposible" if you below 0 with the penalties.

Remember that the rules are the tools of a GM, not the other way around, and that telling a good story is more important than anything else.

Feel free to let the players autofail if the story needs it. Let them have a 2% chance of success if a task is truly heroic, or let them use a temporary fatepoint to succeed with something that is truly good for the story. After all, the players are just servants to the story, and the GM is the slave of the servants.