Matthew Legg and Mark Gilbey from WSP | Parsons Brinckerhoff in the UK presented at the ISAVFT 2015 - Symposium on Aerodynamics, Ventilation and Fire in Tunnels, held in Seattle on September 15-17, 2015.

1. Acceptability of air velocity from a
human thermal comfort and safety
perspective
Matthew Legg and Mark Gilbey
WSP | Parsons Brinckerhoff in the UK

2. Agenda
• Motivation
• Existing guidance
• Effects of air velocity
– Thermal comfort
– Mechanical comfort
– Safety
• Conclusions

3. Why control air velocity?
Stability and life safety
Dynamic forces on
structures
Dust or litter
transport
Passenger
experience
0-3 m/s
4-6 m/s
6-9 m/s
9+ m/s
Normal operations
Emergency operations

4. Existing guidance
Comfort
• Subway Environmental
Design Handbook (SEDH)
• Beaufort Scale
• ASHRAE draught index
• Project design criteria
• EN ISO 7730
• Not easily defined, most
sources cite 3-6 m/s
Safety
• SEDH
• NFPA 130
• TSIs
• Project design criteria
• 11 m/s widely accepted as
safety criterion

5. Refinement of thermal
comfort guidance
• Concept of thermal neutrality
• Heat rejection dominated by
convective heat transfer
• Desirable to:
• Maximize thermally
pleasing air velocities
(cooling breeze)
• Minimize thermally
displeasing draughts
(wind chill)
• Building services indices not
necessarily applicable
EN ISO 7730

6. Refinement of thermal
comfort guidance

7. Mechanical discomfort
Source Limit Effects
SEDH 5 m/s Disruption of clothing (Beaufourt)
Lopes et al. 6 m/s “Very windy” sensation, steady wind and acclimatised
Hunt et al.
6 m/s Increase in perceived wind noise, 10% turbulent intensity
7 m/s People appear “blown about”
• Discomfort or nuisance effects due to intermittent gusts
• Less sensitive to temperature
• More sensitive to unsteadiness or turbulent intensity

8. Safety limits
• Buildings adopt Lawson scale - requires
historical data
• SEDH and NFPA 130 cite ~11 m/s (2200
fpm)
• 11 m/s appears reasonable based on
experimental data
• Corresponds to around 15% of people
with difficulty walking (Lopes)

9. • Stability largely affected by “gustiness”
• Rapid changes in air velocity may occur
spatially and temporally
• Females more susceptible than males
• Reasonable that front facing gusts are
more challenging
• Hunt et al. suggested correction factor
of 1+3*TI for turbulent intensity
Safety limits

10. • Jordan data suggested loss of stability for
aerodynamic forces > 5% of body weight
• Accounts for physiological differences
Average Female 9 m/s
Average Male 10 m/s
• TSIs cite absolute limit of 15.5 m/s on
platforms
Safety limits

11. • Thermal comfort:
• Additional guidance for selection of
comfort criteria
• Mechanical comfort
• Further data around mechanical effects
on people
• Safety
• Improved context on the selection of
safety limits
• Considerations for unsteady air velocities
Conclusions

12. Questions?