Recently you asked me if it would be necessary to have ODH in the SPS due to a new piece of equipment containing 50 liters of liquid helium at 4K and now there are proposals of using bigger quantities. Unfortunately, there is not a rapid answer. Before thinking about the ODH, the safe design according to the applicable design rules shall be guaranteed.
Facts
I understand from our discussion that the cross section of the SPS is similar to the LHC and that the ventilation airflow is 45'0000 m3/h.
50 l LHe = 6.25 kg=35m3 at ambient temperature and pressure
400 l LHe = 50kg= 280 m3
700 l LHe= 875 kg=500m3
Basically it all boils down to a risk assessment:
1. What are the scenarios and probabilities for a helium release?
2. What would the environment be in the SPS tunnel and in the adjacent areas (ODH, temperatures, pressures etc) in the event of a helium spillage?
3. Is it possible to lead the helium from the safety valves (helium enclosure and vacuum enclosure) out from the tunnel out in the open?
You can get ideas from the risk assessment done for the LHC machine cryogenics in 1999 (LHC Project Note 177) and the updated risk assessment following the accident of September 2008 (EDMS 1046841).
Experience from the LHC tunnel:
- Small flows in the order of 0.1kg/s are not considered dangerous for people. However, helium could accumulate at high points and create pockets of trapped helium at height.
- The ventilation flow is very important for the helium distribution in the tunnel.
- The ventilation flow when people have access is 18'000 m3/h and 100% of new air is injected (not re-cycled)
- The temperature of the helium when it enters the tunnel is important for the tunnel environment
- ODH sensors are installed every 300 meters just under the ceiling.
- Two ODH sensors are installed in enlargements where helium could accumulate.
All the best,
Gunnar