Engineering calculations Flashcards
What are some of the model assumptions made for engineering calcualtions?
*People start to evacuate at the same time.
*Movement between egress components is considered.
*Flow does not involve interruptions due to evacuee decisions
*Number of people considered rather than individual attributes
*Evacuees are free of impairments.
*Focuses on physical movement.
*Environmental conditions typically do not impact performance.
*Results are deterministic.
(Not to say an expert user cannot modify calculations.)
What are some factors to consider with regards to the question how much space do crowds need?
Density
Area per person
Personal space preference
Needed to understand comfort and safety req
Level of Service:
–>LoSA – free circulation
–>LoSF – complete congestion
What is Level of Service? (Fruin)
-LoS concept introduced by Fruin (1987)
- Speed and density to define guidelines for comfort and safety
- These areas include space around the person: this is called the body ellipse.
- LoS assumes an elliptical body size for personal space
What is Level of Service? (Kholshevnikov)
- Assuming avg. 0.2 m2/person, possible in theory: 5 people/ m2.
- Kholshevnikov found that more extreme conditions possible
- Assuming average size, stationary and evenly distributed
- As crowd density increases, the ability of the crowd to move decreases
- ↑ packing – ↑risk ↓ comfort, depending on its location and duration.
- At 6+ person/m2, no space between individuals.
- Forces are transmitted : crowd turbulence
- Difficult for people to have ‘agency’
What are the two levels of engineering analysis?
Structure
Component
What are transitions accounting to SFPE?
Performance is a function of specific flow p/m/s, eff width m, spped m/s, desity p/m2
Points in the exit path that
Widen or narrow
Change terrain
Merge occupant flows
Describe the function between density and movement speed. How does the curve look and what are some key data points?
<0,54p/m2 a person can move at chosen speed.
>3,8 p/m2 movement ceases.
horisontal line from 0 to 0,54p/m2 and then linearly decreases down to 3,8p/m2.
Describe the function between density and Specific flow. How does the curve look and what are some key data points?
As population density increases, specific flow increases up to a maximum dens of 1.9p/m2
At higher densities the flow rate falls off to zero at 3,77p/m2
A parabolic curve from 0-3,77p/m2 with a top at 1,9p/m2.
The value of the specific flow varies depending on the kind of component.
What is the effective width?
The unused space at the sides is subtracted from the actual width to allow lateral body sway and assure balance
What is component flow?
Predicted flow passing a particular point or through a component in an exit route
What is “time for passage”?
The time for a population to pass a point in an exit route
What is a rule for hand calculations for transition point?
Flow after a transition is a function of flow into the transition point
What are some points of functionality when it comes to evacuation calculation?
Able to produce a range of different scenarios
Able to quantify egress performance
Based on simple assumptions
Is able, to a degree, to represent different scenarios
Can be used for assessment and procedural design
When it comes to evac calculations there are two orders of estimates; which ones? Explain them
First order estimate critical component. Focuses on component that places the most severe constraint on flow of people.
Second order estimate is a more complete analysis. Clearly identify results and track where you are in the process, it can get complicated
