Thunderhead Engineering Forum

Please login or register.

Login with username, password and session length
Advanced search  


Forum moved to

Author Topic: can you help me  (Read 2665 times)


  • New Member
  • *
  • Posts: 1
    • View Profile
can you help me
« on: October 13, 2013, 04:44:22 am »

I'am a learner. When i practise the provided example, i can't understand the definition used in SFPE mode:door boundary layer. can you explain it to me. Thank you very much. In the document sfpe_example_1, Example 1 :2*(32 in-2*6 in) why minus 6 and why multiply 2.


  • Thunderhead
  • *****
  • Posts: 22
    • View Profile
Re: can you help me
« Reply #1 on: October 14, 2013, 08:22:51 am »

SFPE uses the boundary layer to reduce the effective width of egress components.

From the Engineering Guide "The concept of effective width is based on the observation that people do not generally occupy the entire width of an egress component, staying a small distance away from the walls or edge of the component. Nelson and Mowrer refer to this small distance as a "boundary layer," in keeping with the hydraulic analogy for people movement."

In the example, the door is 32 inches wide and the boundary layer for a door is 6 inches on both sides of the door (that is the reason for 32-2*6). The values of the boundary layer are defined in the SFPE engineering guide and are listed in a spreadsheet you can download at

Daniel Swenson