Architectural standards for deck plans (human scale; all figures rounded 
up to nearest 0.5 ft):

Crawl pipe		2.5 ft diameter
Crawlway		2 ft wide x 3 ft high

Catwalk			2.5 ft wide x 6 ft high
(1 person passing, stooped)

Passageway		3.5 ft wide x 6.5 ft high
(1 person standing, 1 person passing)

Corridor		4.5 ft wide x 6.5 ft high
(2 persons passing)

Doorway			2.5-3 ft wide

Deck hatch		2 ft square or diameter
w/ space suit [sic]	3 ft diameter

Bulkhead access hatch	max 1 ft above deck
			2.5 ft wide x 2.5 ft high

Vertical ladder		2.5 ft wide x 3 ft deep
			0.5 ft from side
			1 ft between rungs
			min 3 ft extend above top deck

Stair ladder		60 degree slope
			2.5 ft wide (one way)
			1 ft between risers
			6-6.5 ft clearance
			rail 3 ft above risers

Decking	and bulkheads	1:20 depth-to-span ratio
			(assuming space frame construction)
	Bulkheads	11-14 ft high (total) x 1 ft thick
	Decking		2-3.5 ft deep x 40-70 ft max span
			8-9 ft head clearance

References:

Ramsey and Sleeper, Architectural Graphic Standards, 7th ed., 1989.
GURPS Traveller, p. 153.