LIQUID NITROGEN

SAFETY DOCUMENTS

CVjAPRILIO

LIQUID NITROGEN: GOLDEN RULES

Know the Emergency Procedure!!

1. LN2 storage tanks are located in room C.27

2. Always wear your safety glasses.

3. Always wear your leather gloves.

4. Always use the rigid syphon and gas phase separator.

5. Always use vessels designed for LN2.

6. Never use plastic, glass or rubber with LN2.

7. Ensure receiving vessel is secure.

8. Open valves slowly and be aware of gas noise from gas phase separator or LN2 pressure relief device.

9. Avoid splashing and use minimum quantity required.

10. Never touch un-insulated pipes or vessels with bare skin.

11 . Never put water into polystyrene LN2 buckets.

12. When filling other vessels use appropriate metal funnels - Always fill "slowly".

13. Never fill detectors , traps etc with LN2 bucket at or above head height.

14. Ifmoving large LN2 tanks, always use the correct trolley and care during transportation.

15. Never accompany large LN2 vessels in lifts

Finally, imagine LN2 like "hot boiling water" - take extreme care at all times!

• The Department ..,j,. i University Of • * Risk Assessment For-mOf Physics &

Sheffield. Astronomy.

PERSONS AT RISK: ( X)ElllP!Oyees (x )Students ()Public (x )Visitors (x) Others Reference No; Risk: (H ) High (M) Medium (L) Low (0) No risk Environment: Laboratorv and storage areas

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SIGNIFICANT HAZARD POTENTIAL CONSEQUENCES OF RATING EXISTING CONTROL/PROPOSED CONTROL MEAS URES RATING HAZA.RD

Liquid between 8L-18L Cold burns Ifrostbite M i.Ensure workplace and work area is well ventilated z.Use minimum quantities necessary 3.Use PPE minimum leather gloves and eve protection L 4.Ensure that all workers are trained and instructed in its use I) . Use only eouiurnent and containers designed for use with LN2 6.Ca1culate maximum quantiti es suitable for the work area

Liquid greater than 18L Asphyxiation due to rapid conversion of H i.Contr ols as listed above } liquid to gas

2. Installation of Oxygen Deficiency sensing where oxygen } concentrations would be lower than 18%in the event of total conversion of liquid to gas Low level sensing approx D.7m from floor level

Cold burns /frostbite 3.0>"j'gen sensor-S monthly calibration & 12 monthly } L reulacernent 4. Emerzencv Procedure in the event of a low oxygen level alarm }

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Emergencx Procedure for

Liquid Nitrogen

In the Research Laboratory

No asphyxiation hazard as maximum quantities should never be exceeded. In case of total spillage, open windows and main door and allow to disperse.

In the Liquid Nitrogen Store (C 27)

A Never enter the room if the Oxygen deficiency alarm is going off (Sounding/flashing) Report immediately to a member of the Liquefier staff

B If the alarm sounds whilst in the room, turn off the liquid withdrawal valve. Open the large swing doors to the Hicks building yard and exit leaving the doors wide open .. Report immediately to a member of the Liquefier staff.

C If the withdrawal valve is stuck or broken in the open position then the following procedures can be followed.

• Try closing the liquid extraction valve. If the valve nearly closes to a trickle of gas then exit via the Hicks yard and inform a member of the Liquefier staff

• If the flow is high and cannot be shut off then fully open the "silver" handled valve on the top of the dewar, ensuring that it is pointing away from yourself and any other people. This will release the over pressure and eventually the liquid will stop flowing.

NOTE Opening the gas phase valve will be noisy, so do not be alarmed.

• Exit into the Hicks yard leaving the doors open and report to a member of the Liquefier staff.

Recommended procedure for transportation of Cryogenic Liquids using the Goods lift

Liquid Nitrogen

Open top dewars - typically the 4L Polystyrene containers should NOT be transported in the lift. In the event of spillage the liquid expansion volume would cause an asphyxiation environment. All such movements should be made using the staircase and no more than two at a time.

Low Pressure sealed dewars (l60L volume) - rarely, if ever should these vessels need to be transported in the lift. If required to do so, it is important that the gas over pressure is reduced to 50% of the relief valve pressure in a well ventilated area. This would be typically 1Opsi/ 0.7 barg. In the event of breakdown , use the emergency alann for assistance, do not panic since the relief valve setting will take more than 12 hours to be reached. It is recommended that such a procedure is undertaken by a member of the liquefier staff.

Liquid Helium

lOOL sealed dewars - commonly transported between C&D floors. Only vessels that have been previously connected to the helium recovery system may be transported. Under these circumstances the dewar overpressure is ~ atmospheric. Upon removal, proceed immediately to your destination, reconnecting the dewar back to the recovery system. Visually check the pressure gauge prior to entering the lift or open bladder inflation valve (if fitted). Please ensure all valves remain closed during transportation and the dewar plug is fitted. In the event of breakdown, use the emergency alann for assistance, do

not panic since the relief valve setting will take more than 12 hours to be reached. Under no circumstances transport dewars that were not previously connected to the recovery line or exhibit any frosting on the top flange. In the latter case seek advice from a member of the liquefier staff.

General 1. Do not to use the passenger lifts unless the goods lift is out of order 2. Always travel alone 3. Try to avoid transportation during Out of Hours

April 2008

Department of Physics and Astronomy

Safe Working Procedure

This form should be completed for each procedure that may be undertak en in the designated area, which has a hazard or potential hazard associated with it.

Each procedure an undergraduate, postgraduate, research associat e, staff member, technician or secretary is expected to perform, must be adequately explained, (with the aid of this form) at the time of their induction into the working area , by a suitably qualified person.

Date: Octob er 2005 Location : Experimental Physics & Astronomy Research Laboratories Name of supervi sor General guide: specific procedure to be determined by individuals

Details of the procedure : LIQUID NITROGEN USE Location for LN2 store is C.27 1.00 not enter the room if the Oxygen Deficiency alarm is sounding or the light is flashing.lmmediately report this to the liquefier staff or senior staff member 2. Never take storage containers(240L Wessington) to a research laboratory unless it has a low level sensor for Oxygen Deficiency monitoring.(See guide for transport ation if moved from C.27) 3.Should the alarm sound , close the stora ge vesse l valve and exit the room . Follow the Emergency Procedure in this event

Important information prior to using LN2 I.Read and understand the guidance notes contained within the cryogenics section of the Laboratory Safety folder situated in each research laboratory 2.Calculate the maximum quantities permitted in the laboratory/work area, but use the minimum that is necessary ( See calculation information) 3. Receiv e appropriate PPE and a practical demonstration from a competent colleague 4. Sign the declaration as a registered and trained user(Pl ease see C.Vickers,C.10) 5. Only use 4L capacity polystyren e containers and carry no more than 2 at anytime . 6. Always use the stairs and not the lift General use I . Only pour into equipment specia lly designed for LN2 2. Use your PPE 3. Avoid splashin g liquid on bare skin, especially the eyes 4. Burns to hands/fingers to be treated as for hot burns

Current safety precautions for this procedure 1. Guidance notes in the Laboratory Safety folder. 2. Read the "Golden Rules " 3. Use PPE 4. Know the Emergen cy Procedure

To calculate the maximum permitted asphyxiant that can be stored in a Laboratory so as to preserve a life sustaining atmosphere in the case of spillage or accidental venting.

Assume that the asphyxiant is fully mixed with the air in the room.

The normal concentration of oxygen is 20.9% Oxygen concentrations below 18% are considered hazardous.

The volume of asphyxiant is therefore given by,

v ==v _0.18VR m' A R 0.209

where VR is the volume of the room in rrr', or

Example: what is the largest volume of liquid nitrogen that can be safely stored in Cll Laboratory, to avoid an oxygen depleted atmosphere?

Data Volume ofCll Laboratory = 127 m3

1 litre of liquid nitrogen is 0.683 rrr' then,

VA == 0.139 X 127 == 17.6 m 3 of gas or

VA = 17.6/0.683 == 25.8 Iitres of liquid equivalent.

Taking a 500/0 safety factor, to allow for the fact that at the point of spill, the oxygen depletion will be highest,

maximum permitted level is == 12.9 litres of liquid nitrogen

(this is equivalent to 3-4 polystyrene buckets full)

You can compare this calculation with the data on the accompanying sheet. Remember also that there can be a natural change of air in a room every ] -2 h.

ROOM OXYGEN CONCENTRATIONS -IN FULLY MIXED ATMOSPHERE - RESULTING FROM LEAK I SPILLAGE

ROOM VOLUMES (in m3) NITROGEN VOLUME 50 100 150 200 250 300 400 500 750 1000 1250 Cylinder (size mm) GAS (m3) OXYGEN CONCENTRATION 140x940 (230 bar) 2.1 X 20.1% 20.5% 20.6% 20.7% 20.8% 20.8% 20.8% 20.9% 20.9% 20.9% 20.9% 230x1460 (230 bar) 9.78 W 16.8% 18.9% 19.5% 19.9% 20.1% 20.3% 20.4% 20.5% 20.7% 20.7% 20.8% 230x1640 (230 bar) 10.78 Z 16.4% 18.7% 19.4% 19.8% 20.0% 20.2% 20.4% 20.5% 20.6% 20.7% 20.8%

CARBON DIOXIDE VOLUME Cylinder (size mm) GAS (m3) OXYGEN CONCENTRATION 140X940 (50 bar) 3.3 19.6% 20.3% 20.5% 20.6% 20.7% 20.7% 20.8% 20.8% 20.9% 20.9% 20.9% 203x870 (50bar) 7.3 17.9% 19.4% 19.9% 20.2% 20.3% 20.4% 20.6% 20.6% 20.7% 20.8% 20.8% 230x1496 (50bar) 18 13.4% 17.2% 18.4% 19.1% 19.4% 19.7% 20.0% 20.2% 20.4% 206.0% 20.6%

ARGON VOLUME Cylinder (size mm) GAS (m3) OXYGEN CONCENTRA TION 230x1460 (230bar) 11.01 16.3% 18.6% 19.4% 19.8% 20.0% 20.2% 20.4% 20.5% 20.6% 20.7% 20.8%

NITROGEN VOLUME LIQUID (Iitres) GAS (m3) OXYGEN CONCENTRATION 10 6.83 18.1% 19.5% 20.0% 20.2% 20.4% 20.5% 20.6% 20.7% 20.7% 20.8% 20.8% 25 17.1 13.8% 17.4% 18.6% 19.2% 19.5% 19.8% 20.1% 20.2% 20.5% 20.6% 20.7% 50 34.1 6.6% 13.8% 16.1% 17.3% 18.1% 18.6% 19.1% 19.5% 19.9% 20.2% 20.4% 100 68.2 0.0% 6.6% 11.4% 13.8% 15.2% 16.2% 17.3% 18.1% 19.0% 19.2% 19.8% 150 102.3 0.0% 0.0% 6.6% 10.2% 12.4% 13.8% 15.6% 16.7% 18.1% 18.8% 19.2% 200 136.4 0.0% 0.0% 1.9% 6.6% 9.5% 11.4% 13.8% 15.2% 17.1% 18.1% 18.7% 250 170.5 0.0% 0.0% 0.0% 3.1% 6.6% 9.0% 12.2% 13.8% 16.2% 17.3% 18.1% 300 204.6 0.0% 0.0% 0.0% 0.0% 3.8% 6.6% 10.2% 12.4% 15.2% 16.6% 17.5% 400 272.8 0.0% 0.0% 0.0% 0.0% 0.0% 1.9% 6.6% 9.5% 13.3% 15.2% 16.4% 500 341 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 3.1% 6.6% 11.4% 13.8% 15.2% 600 409.2 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 3.8% 9.5% 12.4% 14.1%

Oxygen concentrations below 18% must be considered hazardous The calculations above will be valid where the gas is fully mixed with the air in the room. At the point of the leak I spill - the concentration of oxygen will be significantly lower than indicated above. If 2 cylinders are connected via a changeover valve then the maximum volume of gas which could leak doubles, and the resulting Oxygen concentration

can be calculated by halving the room volu me and reading off the Oxygen concentrat ion for the smaller sized room.

Nitrogen 1Nitrogen 2