Safety

Safety protocols- ONLY FOR BACH staff

LHe DEWARS and REFILL

The dewar has a total of five ports:
1. Pressure gauge, which is preceded by a small pressure relief valve.
2. Fine pressure relief valve with a manual valve on it. This valve can be briefly closed during cooldown to facilitate He transfer, but at all other times should be open as it is the initial safety valve in that it has the lowest pressure requirement to open. 
3. Coarse pressure relief valve. This valve will open if the pressure becomes very high, and after the fine pressure relief has already opened.
4. Fill valve for the dewar- SHOULD ALWAYS BE CLOSED. If this valve is left open, air will pull into the dewar and cause an ice plug which could be very dangerous. However, if during installation of the cryostat there is significant overpressure, as judged by the release of He through the fine and/or coarse pressure relief valves the fill valve can temporarily be opened to release overpressure.
5. Fill valve for the dewar- SHOULD ALWAYS BE CLOSED. If this valve is left open, air will pull into the dewar and cause an ice plug which could be very dangerous. However, if during installation of the cryostat there is significant overpressure, as judged by the release of He through the fine and/or coarse pressure relief valves the fill valve can temporarily be opened to release overpressure.
6. Top port through which the transfer line vessel leg is inserted. It should ALWAYS BE CLOSED when the dewar is not in use as otherwise an ice plug can be formed.
Before the installation of the cryostat is started, the valve for the top port should be opened to release any overpressure of the dewar. As cold gas will be expelled through this port immediately upon opening the valve, make sure that hands and face are protected.

As an absolute rule - ALWAYS WEAR THICK GLOVES AND SAFETY GLASSES AND CLOSED SHOES, LONG PANTS AND LONG SLEEVES (NO UNCOVERED SKIN) WHEN WORKING WITH THE LHe and LN2 DEWARS. FOR ALL VALVES, THE VALVE IS OPEN WHEN THE HANDLE IS PARALLEL TO THE RELATED TUBES, AND CLOSED WHEN PERPENDICULAR TO THE RELATED TUBES.

(information taken from: http://www-ssrl.slac.stanford.edu/smbxas/instrumentation/cryoman.html#frost).
 

Using Compressed Gas


Use only wrenches or tools provided by the cylinder supplier to remove a cylinder cap or to open a valve. Never use a screwdriver or pliers. Keep the cylinder valve closed except when in use. Attach the closed regulator to the cylinder. Never open the cylinder valve unless the regulator is completely closed. Regulators are specific to the gas involved. A regulator should be attached to a cylinder without forcing the threads. Ensure the threads of both the regulator and main valve are clean. If the inlet of a regulator does not fit the cylinder outlet, no effort should be made to try to force the fitting. A poor fit may indicate that the regulator is not intended for use on the gas chosen. Turn the delivery pressure adjusting screw counter-clockwise until it turns freely. This prevents unintended gas flow into the regulator. Open the cylinder slowly until the inlet gauge on the regulator registers the cylinder pressure. If the cylinder pressure reading is lower than expected, the cylinder valve may be leaking. With the flow control valve at the regulator outlet closed, turn the delivery pressure adjusting screw clockwise until the required delivery pressure is reached. Check for leaks using Snoop or soap solution. At or below freezing temperatures, use a glycerin and water solution, such as Snoop, rather than soap. Never use an open flame to detect leaks. When finished with the gas, close the cylinder valve, release the regulator pressure and replace the gas cap if it will not be used in the near future.

 

Procedure to access the FE hutch and radiation emergency 

pdf "The personal safety of BACH beamline".

 

Magnetic fields and cryomagnet endstation Hazard and Safety

 

First we remind that it is forbidden for the users to access the high platform around the cryomagnet and that it is forbidden to leave the beamline unattended when the magnetic field is on.

Special care has to be observed when operating with the superconducting coil since high magnetic field is generated in the area around the cryomagnet.
The area where the magnetic field can be potentially dangerous is delimited and closed by gates and it is a RESTRICTED ACCESS ZONE. In particular it is forbidden to enter in this area when a magnetic field has been applied (even if the current of the coil is zero).  
The magnetic field can be dangerous. The field measured outside the cryomagnet is 145 milliTesla when the SC coil is operating at 6 T, which is a quite high value. 
Before operating with the magnet please read the following safety and precautions rules:
BEFORE RAMPING UP THE SC COIL: REMOVE all metallic objects which could be attracted by the magnetic field (screwdrivers, screws, bolts, nuts, ....), credit cards, self phones, watches, from the magnetic field area (restricted zone delimited by the gates)!!

Exposure should be always avoided for pregnant women, people with  cardiac pacemaker, neurostimulators, cochlear implant, derivation valves, lenses, intra-corporeal metallic foreign objects

In this table we report the magnetic field measured along the field at 314 mm from the center of the coil (maximum field in the restricted area external to the cryomagnet): 

coil (T) coil (A) external field (G,mT)
0 0 3.4G-0.34mT
-0.1 -1.439 22.4G-2.24mT
-0.2 -2.878 43.3G-4.33mT
-0.5 -7.195 106G-10.6mT
-0.75 -10.79 161G-
-1 -14.39 215G
-2 -28.78 435G-43.5mT
-3 -43.175 665G-0.665mT
-4 -57.56 904G-0.904mT
-5 -71.96 1147G-114.7mT
-6 -86.35 1389G-138.9mT
 

▪ Projectile effect (attraction by a static magnetic field and acceleration, with speeds of up to several meters per second): ferromagnetic material (if in doubt about the ferromagnetic nature of a metal object, a test can be carried out using a small magnet). REMOVE all metallic objects which could be attracted by the magnetic field (screwdrivers, screws, bolts, nuts, ....) from the magnetic field area!! Always be aware that even a small object can become a projectile and cause fatal injuries.Due to the presence of a strong magnetic field, certain materials may present a functional or even a vital risk:

▪ Displacement of intra-corporeal metallic foreign objects: Intraocular metallic foreign body (metal worker, history of ballistic orbit trauma, old intra-cranial aneurysm clips)

▪ Perturbed functioning of certain devices: cardiac pacemaker, neurostimulators, cochlear implant, derivation valves, lenses

▪ Credit cards, mobile self phones, watches, tape recorders and cameras, magnetic cards can be permanently damaged and information contained could be corrupted and should stay outside the magnetic field area)

• Electrical transformers may become magnetically saturated in fields above 50 gauss. The safety characteristics of equipment may also be affected.
In regard to prostheses, non ferromagnetic materials with no electrical activity (titanium and its alloys, nitinol, tantalum, etc.) carry no particular risks in relation to magnetic field. For low magnetic prostheses (orthopedic material), a delay of 6 to 8 weeks after implantation is advised to avoid displacing the material.
In all cases, it is advisable to check the magnetic field compatibility of the material (see http://www.mrisafety.com/), particularly when operating in high fields.

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Last Updated on Thursday, 14 October 2021 14:08