GENERAL CRYOGENIC SAFETY TRAINING

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April 2010

OUTLINEIntroduction Basic hazards Physics behind the hazards Protection from cryogenic hazards Applicable FESHM chaptersPortable vacuum insulated

containers (Dewars)Lessons learned

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INTRODUCTIONCryogenic liquids are liquefied gases that are

kept in their liquid state at very low temperatures.

Cryogenic liquids have boiling points below -150 oC (-238 oF).

The most commonly used cryogenic fluids at Fermilab are argon (Ar), nitrogen (N2), helium (He) and hydrogen (H2). These fluids are used in liquid and gaseous forms.

Cryogenic fluids have the potential for creating dangerous working environments.

Everyone who works with cryogenic fluids must know their hazards and how to work safely with them.

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CRYOGENIC HAZARDSExtreme Cold HazardOxygen Deficiency Hazard (ODH)Fire HazardOxygen Enriched HazardOver Pressurization or Explosion

due to Rapid ExpansionHigh Noise Levels Material Embrittlement

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EXTREME COLD HAZARDCryogenic liquids and cold vapors can cause

thermal burn injuries.Brief exposures may damage tissue (eyes, skin,

etc).Breathing of extremely cold air will damage

lungs.Prolonged contact of the skin with cold surfaces

will cause frostbite.The skin, when not protected, can stick to

metal that is cooled by cryogenic liquids and when pulled away the skin can tear.

Even non-metallic materials are very dangerous to touch at cryogenic temperatures.

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OXYGEN DEFICIENCY HAZARD

ODH is caused due to oxygen displacement. ODH is a serious hazard that usually occurs without any

warning. As cryogenic liquid warms up it becomes a gas, but the gas

is still very cold. With Argon and Nitrogen, the gas is also heavier than air. This cold, heavy gas does not disperse very well and can accumulate in surrounding areas displacing the air.

Some gases (He, H2) while cold may be lighter than air. They will mix with surrounding air, will warm-up and stratify, but still present an oxygen deficiency hazard.

Be aware of the hazards associated with large volumes of cryogens in small spaces (for example, use of a portable dewar in a small room)

For more information on ODH refer to FESHM Chapter 5064

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FIRE HAZARD Flammable cryogenic gases like H2 can burn or

explode. Hydrogen is colorless, odorless, non-toxic, highly

flammable and explosive in the presence of air or oxygen in the right concentration. It forms a flammable mixture when it exists at 4 to 74%. Hydrogen, since it is lighter than air, will tend to form pockets of gas along ceilings, which can lead to an explosion or fire hazard.

A flashing or rotating blue light is used at Fermilab to indicate that hydrogen is present in experimental apparatus in the area

Further training is required for qualification for working with hydrogen.

For more details on H2 safety refer to FESHM Chapter 5032.2.

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OXYGEN ENRICHED AIRCryogenic fluids like liquid helium (LHe), liquid

nitrogen (LN2) and liquid hydrogen (LH2) are so cold that they can easily liquefy the air they come in contact with.

This liquid air can condense on surfaces cooled by LHe, LN2 and LH2.

Due to the smaller latent heat of N2 compared to Oxygen (O2), the N2 will evaporate more rapidly, leaving behind a liquid air mixture which has a high concentration of oxygen.

This O2 enriched air presents highly flammable atmosphere.

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OVER PRESSURIZATIONWithout adequate venting or pressure-relief

devices on closed containers containing cryogens, enormous pressures can build up.

The pressure can cause an explosion.Unusual or accidental conditions such as an

external fire, or a break in the vacuum which provides thermal insulation, may cause a very rapid pressure rise.

The pressure relief valve must be properly installed and free from obstruction.

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Material EmbrittlementMost engineering materials such as metals and

ceramics are made up of crystals. The material’s crystalline structure determines how the material is affected by embrittlement.

Most Face Centered Cubic (FCC) structure materials remain ductile at cryogenic temperatures. Examples of FCC materials include Aluminum, Copper, Silver, Gold, Nickel, Palladium, Platinum, and some stainless steels

Most Body Centered Cubic (BCC) materials become brittle at low temperature. Examples of BCC materials include Molybdenum, Zinc and most plastics. 10

PHYSICS BEHIND HAZARDS

Force = pressure x area ◦ Vacuum load on 3 foot diameter portion of

evacuated vessel = 15,000 lbs ◦ 1/2-inch valve stem with 250 psi shoots out

at over 40 ft/secExpansion of liquids to gas

◦ 1 to 800 expansion ratio from liquid nitrogen or helium to room-temperature gas

◦ Closed volume reaches 12,000 psi

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PROTECT YOURSELFAlways wear personal protective equipment while

handling cryogenic liquids. This includes: thermal insulated gloves, face shields, hearing protection, long sleeve shirts, trousers, and safety shoes.

Only trained and qualified personal should be allowed to handle, transport or store liquefied gases.

Proper storage is essential for cryogenic fluids.Make sure that pressures are acceptable before

operating.Stand away from vents and reliefs.Be aware of closed volumes into which liquid

cryogens might leakUse cryogens in properly ventilated areas only

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IF EXPOSEDIf you suffer a cryogenic burn

(frostbite), slowly raise the temperature of the affected area back to normal.◦For minor burns

Do not pull clothing away from the area but loosen any clothing that may restrict blood circulation and make the person comfortable.

Place the affected area in lukewarm (<40oC) water.

◦For major injuries call x 3131April 2010

General Cryo Safety Training13

RELEVANT FESHM CHAPTERS

5031 Pressure Vessels5031.1 Pressure Piping Systems5031.2 Helium Tube Trailer Connections &

Onsite Filling Guidelines5031.3 Gas Regulators5031.4 Inspection and Testing of Relief Systems5031.5 Low Pressure Vessels

5032 Cryogenic System Review

5032.1 Liquid Nitrogen Dewar Installation and Operation Rules

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RELEVANT FESHM CHAPTERS (PG. 2)

5032.2 Guidelines for the Design, Review and Approval of Liquid Cryogenic Targets

5032.3 Transporting Gases in Building Elevators

5033 Vacuum Vessel Safety

5034 Pressure Vessel Testing

5034.1 Retesting Procedures for D.O.T. Gas Storage Cylinders Including Tube Trailers

5063 Confined Spaces

5064 Oxygen Deficiency Hazards (ODH)

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5032 CRYOGENIC SYSTEMS

Scope - “This chapter describes procedures for reviewing the safety aspects of cryogenic systems as well as the required occupational training for cryogenic personnel.  It pertains to all cryogenic systems including, for example, those used for refrigerating magnets, hydrogen targets, argon calorimeters, or as a source of gas.  It also includes cryogenic systems supplying purge gas for detectors where the stored liquid inventory is greater than 200 liters.”

Review is required for new systems and after significant changes are made.

The chapter specifies documentation requirements and review process

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5031 PRESSURE VESSELSScope - “This chapter applies to any vessel

used at Fermilab that falls within the scope of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section VIII.”

Scope of ASME Boiler and Pressure Vessel Code, Section VIII, is basically ◦ 15 psi differential pressure and > 6

inches diameter “An Engineering Note shall be prepared by an

engineer or designer for all existing or new operational pressure vessels at Fermilab”

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5031.1 PRESSURE PIPING“All pressure piping systems built and used at

Fermilab shall be in accordance with this chapter and the ASME/ANSI B31 code series.”

Review must occur when ◦ Pressure x Volume > 150,000 ft-lb (for

example, about 210 feet of 3-inch pipe at 100 psig) or

◦ Pressure > 150 psi for gas, 500 psi for liquid ◦ Cryogenic piping of any size (due to low

temperature) Various exceptions and other rules also apply.

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5033 VACUUM VESSELS A vacuum vessel is defined as

◦ Over 12 inches diameter ◦ Total volume greater than 35 cubic feet ◦ Vessel under external pressure with Pressure

x Volume > 515 psi-ft3 ASME code design rules apply in certain ways

as described in the chapter. An engineering note and review are required.

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5064 ODHAn ODH area is one where the oxygen level

could drop to below dangerous levels (<19.5% oxygen)

This chapter describes the hazard mitigation procedure in detail

Special training and qualifications are required to work in ODH areas

An engineering note and review are required.

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PORTABLE DEWARS• Portable cryogenic Dewars to store and transport

cryogenic fluids are widely used at Fermilab• When using portable Dewars be aware of general

cryogenic hazards• Use PPE when handling portable Dewars• Dewars shall be operated and stored in a well

ventilated area. o DO NOT STORE OR OPERATE DEWARS IN CLOSETS,

OFFICES, SMALL LABS OR POORLY VENTILATED AREAS• Dewars shall be operated and stored in a vertical

position. o DO NOT STORE, SHIP OR OPERATE DEWARS ON A SIDE

• Dewars should be moved using dolly or appropriate cylinder carts.

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TYPICAL PORTABLE DEWARS

160 Liter LN2 Dewar, 230 PSIG with pressure building and CGA connection, Airgas ID-NI160LT230PB

160 Liter LN2 Dewar, 22 PSIG with pressure building for liquid withdraw, Airgas ID-NI160LT22PB

160 Liter LAr Dewar, 230 PSIG with pressure building and CGA connection, Airgas ID-AR160LT230

Dewars can be ordered for delivery at Ext-3808Specialty Dewars with different volume and

pressure ratings are also available upon request

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TYPICAL PORTABLE DEWAR SCHEMATIC

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Liquid Withdraw Relief Valve Pressure Gauge

Rupture Disc

CGA Connector For Gas Withdrawal

Vent Valve

Liquid Level Gauge

Pressure Building Circuit

USE PROPER PPE

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Safety shoes

Cryogenic gloves

Face shield

Long pants and sleeves

Ensure Dewar Is Properly Connected To the Cylinder Cart

TRANSPORTING DEWARS

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TRANSPORTING DEWARS, CONTINUED

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DEWAR GAS WITHDRAWAL

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• Purge Regulator Connected To CGA Fitting For Gas Withdraw

LESSONS LEARNEDThe following slides are a set of “lessons

learned” which have been compiled from various sources.

One primary source of lessons learned is the American Industrial Hygiene Association, which has a section on their website describing several cryogenic accidents: ─http://

www.aiha.org/insideaiha/volunteergroups/labHandScommittee/Pages/IncidentsCryogens.aspx

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LESSONS LEARNED Empty 55 gallon drum (1999)

◦ At the Nevada Test Site, a waste handler was opening new, empty 55 gallon open-top drums. Upon removing the bolt from the drum lid clamp, the ring blew off and the lid was ejected approximately 5 to 10 feet in the air, just missing the Waste Handler's face. The drum did not hiss or show signs of pressurization.

◦ Because the Waste Handler had been properly trained to stand away from the drum while opening it, he was not injured.

◦ The event was caused by the drums being manufactured and sealed at sea level in Los Angeles and subsequently shipped to a much higher elevation of approximately 6,000 feet at the Nevada Test Site. The increased elevation, combined with the midday heat, created sufficient pressure buildup to cause the lid to blow off when the ring was being released.

Large Force Will Result From Small Pressure Applied To A Large Area

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LESSONS LEARNED • Workers wheeled a laboratory dewar to a core room to refill it

from a large liquid nitrogen tank. When they inserted the hose into the dewar and opened the valve on the large tank, the hose whipped out of the dewar, spraying them with liquid nitrogen. Although cryogenic liquids have a high potential for causing burns, they were not injured even though they were splashed in the face and not wearing any eye/face protection.– Possible causes: the valve was opened too far, too quickly,

imparting a whip-like motion on the fill hose. The hose was not secured when the valve was opened. A new filter nozzle had been installed and the users may not have been familiar with its use.

Wear PPE (a face shield, gloves, long pants and long sleeve) when working with cryogenic fluids. If not familiar with a procedure or unsure, ask your supervisor for guidance.

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LESSONS LEARNED 50 liter LN2 laboratory dewar explosion

◦ Transfer of LN2 from 160 liter dewar to 50 liter “laboratory” dewar .

◦ Flex hose end from 160 l dewar would not fit in lab dewar neck (normally a “wand” is inserted for filling), so a connection was made with rubber hose over the OUTSIDE of the lab dewar neck and transfer hose end.

◦ “Slot” cut in rubber hose for vent .◦ Failure not initially caused by overpressure, but by cooling of

upper part of neck during fill! Seal between neck and vacuum jacket broke due to differential thermal contraction.

◦ Seal to vacuum jacket broke after lab dewar nearly full, subsequent overpressure with lack of sufficient vent caused explosion of lab dewar

◦ One person badly injured .

Rupture of insulating vacuum with restricted venting resulted in explosion

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LESSONS LEARNED • Injury due to high-pressure gas venting :

– Pressure was building in a large cryogenic system due to inventory warming (a result of low capacity caused by contamination problems, turbine inlet filters plugging).

– Operators were ordered to open a 3-inch ball valve with 240 psi behind it to vent system pressure and prevent compressor shutdown on overpressure.

– Operators did not initially wear hearing protection.

– After the operator opened the valve, he was sucked into the stream and blown against a tank, received a head injury requiring stitches.

Inappropriate orders from control room and lack of experience led to an accident. Question instructions if

they seem confusing or unsafe.

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LESSONS LEARNED Two workers at an industrial plant were inspecting a flange surface on

a 48” diameter pipe with an ultraviolet light.

They draped black plastic over the end of the pipe to create shade for seeing any glow from material in the ultraviolet.

The workers did not know there were some sources of nitrogen connected to the pipe. In fact, one of the workers had helped to start a purge on another section of pipe. But the system was so complex, he did not know they were connected.

When they went under the cover to do the inspection, both workers quickly passed out from lack of oxygen. One died; the other was seriously injured.

OSHA ultimately cited the company for violation of the confined space entry standard.

Be aware of potentially confined spaces, possible unlabeled ODH hazards

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RESOURCES• Before starting any project, whether designing,

assembling, renting, installing, or operating a cryogenic system of any size,

ASK YOURSELF:

1. What FESHM and/or other standards apply to this system?

2. What potential safety hazards are involved? (ODH, Pressure, etc.)

FOR ADDITIONAL INFORMATION REGARDING CRYOGENIC SAFETY ISSUES CONTACT YOUR SUPERVISOR AND AREA SAFETY REPRESENTATIVE

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SIGNIFICANCE OF CRYOGENIC HAZARD

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SIGNIFICANCE OF CRYOGENIC HAZARD

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