HET Closure Policy

Dated 12 Oct 2016

  Closure Conditions Warning Conditions
Wind >5 wind gusts over 40 mph in a 5 min interval.
Gusting over 45 mph
Average wind speed over 40 mph
Gusting reaches 35.0 mph
Average reaches 30.0 mph
Relative Humidity Maximum RH over 97.5%
Average RH over 96%
Rain detection in last 10 min.
Maximum RH over 95.5%
Average RH over 90.0%
Dust 1 µm dust count over 100,000
0.3 µm dust count over 6,000,000
Please note the special actions to protect the optical surfaces listed below
1 µm dust count over 50,000
Dust and Humidity The dust/humidity relationship is defined by a flat line to point A from 0 percent humidity
then sloping to point B at which point it is constant to 95% humidity
1 µ A = 25% humidity and 100,000 and B = 60% humidity and 50,000
0.3 µ A = 25% humidity and 2,800,000 and B = 60% humidity and 6,000,000
Suddenly increasing dust   and increasing humidity
Smoke The smoke closure criteria are the same as the dust and humidity closure criteria plus:
large ash particles (larger than 1 um sometimes up to 1 cm in size) in flashlight beam
The distinct smell of smoke
Please note the special actions for smoke and dust closure below
Dewpoint Based on 5 minute averages

(Ext Temp - Ext Dewpoint) < 1.5C
OR
(Tracker Temp - Ext Dewpoint) < 0.5C


A WARNING TO CHECK FOR CONDENSATION:
based on 5 minute averages

(Ext Temp - Ext Dewpoint) < 2.0C
OR
(Tracker Temp - Ext Dewpoint) < 1.0C


A WARNING TO WARM THE DOME:
based on 5 minute averages

(Int Temp - Int Dewpoint) < 1.0C
OR
(Tracker Temp - Int Dewpoint) < 1.0C
OR
(Ext Temp - Int Dewpoint) < 1.0C

Temperature Outside of range -10 to 35C Outside of range -5 to 30C
Threat of Precipitation Rain Sensor on either Mountain
OR
TO's Assessment of Threatening Clouds
OR
The distinct sound of thunder


Special TO closure actions for dust and smoke
  • translide to 3
  • calibration screen in
  • air conditioning in the control room off (to avoid drawing in smoke)
  • air conditioning in the dome on
  • park the instruments to close any covers



    Last updated: Fri, 16 Dec 2016 23:04:43 -0600 shetrone



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