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 counts per cubic foot 0.3 µm dust count over 6,000,000 counts per cubic foot 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 counts per cubic foot and B = 60% humidity and 50,000 counts per cubic foot 0.3 µ A = 25% humidity and 2,800,000 counts per cubic foot and B = 60% humidity and 6,000,000 counts per cubic foot			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