Help with Trap CR

[steerpike65]

Any advice for estimating the CR of the below trap would be greatly appreciated:

Acid Pit Trap CR ??
Any object weighing more than 100 pounds causes the floor to collapse, dropping anyone in the area of the trap 40 feet into a pit with a 10 foot deep layer of acid at the bottom.
Type mechanical; Perception DC 20; Disable Device DC 15
Effects
Trigger location; Reset manual
Effect 40-ft.-deep pit (1d3 non-lethal falling damage plus 10d6 acid per round of contact); DC 20 Reflex avoids; multiple targets (all targets in a 10-ft.-square area)

Thanks.

[Reecy]

CR 1

[steerpike65]

Reecy wrote:

CR 1

How did you figure that? I suspect that may be a bit low for a trap that does 10d6 acid damage per round!

[Reecy]

Thats because of of the low Reflex Save to Avoid. It has a stipulation of minimum weight so not all PCs would activate it based on Race...

The Disable is very low.

[Blue_Drake]

The disable isn't really in line with the damage involved. 10d6/round is lethal for lower level PCs, but a 15 Disable is low for higher level ones.

What level are your PCs?

[Reecy]

yeah you could take a 10 at level 1 with masterwork tools.

Depending on the Disable and the perception checks it is really easy to avoid.

If you want a Stronger Version of that trap

Extend the Trap 5 ft Square on both Sides so the Reflex is 15 + an Acrobatics check of 15 to 20 (Standing Jump no running Start)

Add Smooth walls - Crazy difficulty to get out
Perception make it 25 to 35

Disable 25

this is probably about a CR 5 to 7

So this Pit is actually going to be 15 or 20 ft long and 10 ft wide
And it does not trigger until you are in the middle of so to disable it you are standing on it.

[steerpike65]

The pit is covered by a mushroom cap so it's relatively easy to 'disable' if you see it - just move it off the top. I actually wondered if 15 was too high!! but it's a big, unwieldy, rotting mushroom cap so...

The mushroom cap is being crossed regularly by a Small race so it needs to be OK for them to cross - it's the 'bypass' (for now).

I'm really not too worried about the disable or Reflex saves, the size of the pit, etc. The pit has been created by the acid so would have smooth sides.

The PCs are 5th level so I'm hoping to hit roughly a CR 5.

I guess the real difficulty I'm having is the 10d6 damage per round. When looking at the trap CR calculator in the CRB the damage aspect is calculated at average damage - how do you calculate 'average damage' for 10d6 per round?

[I3igAl]

I would add a climb DC to get out and then go with the damage for like 2 rounds.

[steerpike65]

OK, I'm calculating as follows:

1. Perception DC 20 (it's dark underground, the mushroom cap is the same colour as the floor of the cave but it's a different texture): +0 CR
2. Disable Device DC 15 (it's a big mushroom cap, so can just be lifted off the top of the pit but it's size makes it awkward and it is rotting so could collapse causing a PC to fall in as it does so): -1 CR
3. Trigger (location) and reset (manual): +0 CR
4. Reflex save DC 20 (it's a standard enough 10 ft deep pit): +0 CR
5. Multiple Targets: +1 CR

All the above add up to a 0 CR but then the damage kicks in and the difficulty of getting out should be factored in (thinking on the comments above, I'm thinking a Rough Surface (DC 25) so hard to get out of).

Remaining factors to decide on:
1. Does not affect light/small creatures: -1 CR??
2. DC 25 Climb check: +1 CR??
3. 10d6 acid damage per round (average 30?? 35?? hp per round), which is +3 CR per round. Is 2 rounds reasonable for damage calculation? If so, CR 6??