Here is a response I got from someone I know from Des Moines PD. He's a Master Sergeant there, so he's been around for a while.
Aaron, you are correct. You will find most laws pertaining to the possession and carrying of dangerous weapons in Title 9 of the RCW. I cannot find laws pertaining to length of the blade. The laws cover how the weapon is carried or displayed. Laws also cover knives that are opened by spring or other mechanical type device.
Different cities have their own local codes. I just checked our DMMC on the city's web site. I cannot find any codes referencing knives (I know we used to have some, but perhaps they have been changed). Our codes adopt RCW by statute.
Bottom line, if it is not a spring loaded knifeor some similiar openingmechanical device, it would appear to fall within the law.
[line] From: firstname.lastname@example.org [mailto:email@example.com]
To: Bob Collins
Hi Bob, I was curious if you could help me out on finding a particular weapons law for the state of Washington. I've visited apps.leg.wa.gov and reviewed the weapons statute, but I'm unable to find any particular law that mentions how long a concealed folding pocket knife may be. Do you know if the state itself has a law on blade length, or is blade length of concealed folding pocket knives left up to county and city laws?
From what I gathered from the information on the website, certain blades are legal to carry as long as there isn't an intent to conceal or furtively carry?