Lab Safety

1
Lab Safety

• Dr. R. Forrest
• Phys 3110
• University of Houston

2
Electrical Safety
3
Introduction

• An average of one worker is electrocuted on the
  job every day
• There are four main types of electrical injuries
• Electrocution (death due to electrical shock)
• Electrical shock
• Burns
• Falls

4
Electrical Terminology

• Current the movement of electrical charge
• Resistance opposition to current flow
• Voltage a measure of electrical force
• Conductors substances, such as metals, that
  have little resistance to electricity
• Insulators substances, such as wood, rubber,
  glass, and bakelite, that have high resistance to
  electricity
• Grounding a conductive connection to the earth
  which acts as a protective measure

5
Electrical Shock

• Received when current passes through the body
• Severity of the shock depends on
• Path of current through the body
• Amount of current flowing through the body
• Length of time the body is in the circuit
• The maximum safe shock duration at 110 V is 1
  second (IEEE Std. 80)
• LOW VOLTAGE DOES NOT MEAN LOW HAZARD

6
How Electrical Current Affects the Body
Current (Amps) Human Reaction
0.001 Perception level. Just a faint tingle.
0.005 Slight shock felt not painful but disturbing. Average individual can let go.
0.006-0.025 (Women) Painful shock, muscular control is lost.
0.009-0.030 (Men) This is called the freezing current or "let-go" range.
0.050-0.150 Extreme pain, respiratory arrest, severe muscular contractions, ventricular fibrillation is possible.
1 - 4.3 Ventricular fibrillation.
10 Cardiac arrest, severe burns and probable death.
Note some smaller microwave ovens use 10.0 Amps
(10,000 milliamps) and common florescent lights
use 1 Amp (1,000 milliamps) Source GE Safety
7
Dangers of Electrical Shock

• Currents greater than 75 mA can cause
  ventricular fibrillation (rapid, ineffective
  heartbeat)
• Will cause death in a few minutes unless a
  defibrillator is used
• 75 mA is not much current a small power drill
  uses 30 times as much

Defibrillator in use
mA milliampere 1/1,000 of an ampere
8
How is an electrical shock received?

• When two wires have different potential
  differences (voltages), current will flow if they
  are connected together
• In most household wiring, the black wires are at
  110 volts relative to ground
• The white wires are at zero volts because they
  are connected to ground
• If you come into contact with an energized (live)
  black wire, and you are also in contact with the
  white grounded wire, current will pass through
  your body and YOU WILL RECEIVE A SHOCK

9
How is an electrical shock received?(contd)

• If you are in contact with an energized wire or
  any energized electrical component, and also with
  any grounded object, YOU WILL RECEIVE A SHOCK
• You can even receive a shock when you are not in
  contact with a ground
• If you contact both wires of a 240-volt cable,
  YOU WILL RECEIVE A SHOCK and possibly be
  electrocuted

10
Electrical Burns

• Electrical Burns cause tissue damage, and are the
  result of heat generated by the flow of electric
  current through the body.
• Most common shock-related, nonfatal injury
• Occurs when you touch electrical wiring or
  equipment that is improperly used or maintained
• Typically occurs on the hands
• Electrical burns are serious injuries and need to
  receive immediate medical attention.

11
Involuntary Muscle Contraction6 - 9 mA

• Muscles violently contract when stimulated by
  excessive amounts of electricity
• These involuntary contractions can damage
  muscles, tendons, and ligaments, and may even
  cause broken bones.
• If the victim is holding an electrocuting object,
  hand muscles may contract, making it impossible
  to drop the object.
• Note injury or death may result from a fall due
  to muscle contractions.

12
LOW VOLTAGE DOES NOT IMPLY LOW HAZARD!

• Muscular contraction caused by stimulation does
  not allow a victim to free himself from a circuit
• The degree of injury increases with the length of
  time the body is in the circuit.
• Thus even relatively low voltages can be
  extremely dangerous.
• An exposure of 100mA for 3 seconds can cause the
  same amount of damage as an exposure of 900mA for
  0.03 seconds

13
Inadequate Wiring Hazards

• A hazard exists when a conductor is too small to
  safely carry the current
• Example using a portable tool with an extension
  cord that has a wire too small for the tool
• The tool will draw more current than the cord can
  handle, causing overheating and a possible fire
  without tripping the circuit breaker
• The circuit breaker could be the right size for
  the circuit but not for the smaller-wire
  extension cord

Wire gauge measures wires ranging in size from
number 36 to 0 American wire gauge (AWG) For safe
current limit estimates, see the AWG current
rating tables
14
Inadequate Wiring Hazards

• Most of our wires in Phys 3113/3114 are 20 AWG,
  rated at 5 Amps.

15
Overload Hazards

• If too many devices are plugged into a circuit,
  the current will heat the wires to a very high
  temperature, which may cause a fire
• If the wire insulation melts, arcing may occur
  and cause a fire in the area where the overload
  exists, even inside a wall

16
Electrical Protective Devices

• These devices shut off electricity flow in the
  event of an overload or ground-fault in the
  circuit
• Include fuses, circuit breakers, and ground-fault
  circuit-interrupters (GFCIs)
• Fuses and circuit breakers are overcurrent
  devices
• When there is too much current
• Fuses melt
• Circuit breakers trip open

17
Grounding Hazards

• Some of the most frequently violated OSHA
  standards
• Metal parts of an electrical wiring system that
  we touch (switch plates, ceiling light fixtures,
  conduit, etc.) should be at zero volts relative
  to ground
• Housings of motors, appliances or tools that are
  plugged into improperly grounded circuits may
  become energized
• If you come into contact with an improperly
  grounded electrical device, YOU WILL BE SHOCKED

18
Grounding Path

• The path to ground from circuits, equipment, and
  enclosures must be permanent and continuous
• Violation shown here is an extension cord with a
  missing grounding prong

19
Hand-Held Electric Tools

• Hand-held electric tools pose a potential danger
  because they make continuous good contact with
  the hand
• To protect you from shock, burns, and
  electrocution, tools must
• Have a three-wire cord with ground and be plugged
  into a grounded receptacle, or
• Be double insulated, or
• Be powered by a low-voltage isolation transformer

20
Clues that Electrical Hazards Exist

• Tripped circuit breakers or blown fuses
• Warm tools, wires, cords, connections, or
  junction boxes
• GFCI that shuts off a circuit
• Worn or frayed insulation around wire or
  connection

21
Summary

• Hazards
• Inadequate wiring
• Exposed electrical parts
• Wires with bad insulation
• Ungrounded electrical systems and tools
• Overloaded circuits
• Damaged power tools and equipment
• Using the wrong Personal Protective Equipment and
  tools
• Overhead powerlines
• All hazards are made worse in wet conditions

• Protective Measures
• Proper grounding
• Using GFCIs
• Using fuses and circuit breakers
• Guarding live parts
• Proper use of flexible cords
• Training

22
In Case of Emergency

• Call 911
• Fire Extinguisher in hallway

23
References

• www.osha.gov/SLTC/etools/construction/electrical_
  incidents/mainpage.html

24
Cryogen Safety
25
Hazards from cryogens and their use

• Gases expand by 600 to 1000 times their liquid
  volume.
• Rapidly boiling liquids can displace oxygen,
  oxygen deficiency hazard (ODH)
• Boiling liquids create pressure
• Gases are present beyond the fog cloud
• Liquids are extremely cold.
• Nitrogen (77 K)
• Helium (4 K) will solidify air
• Valves will freeze water and accumulate frozen
  water vapor
• Most things instantly freeze and stick when
  contacting cold surfaces
• Cold liquids can soak into loose-knit fabrics
• Exhaust gases are extremely cold.
• Gases easily permeate even tightly woven cloth
  (perhaps gloves)
• Gases freeze water vapor and possibly air
• Vacuum spaces in (glass) dewars may implode.

26
Physiological Hazards

• Contact Burns/Frostbite
• Asphyxiation/Toxicity
• Hypothermia

27
The highest risks here (my opinion)

• Hazard
• Pouring LN2 into ones shoes or gloves
• Freezing ones hand, perhaps through a glove, on
  a cold surface or transfer line
• Cold He gas burn
• Spatter injury, e.g. from broken plastic hose or
  rapid contact between hot and cold
• Significant cryogen release due to magnet quench
• Continuous venting of a soft dewar (ODH)

• Controls
• Apron or lab coat, pants (no cuffs) over shoe
  tops (closed toe shoes!)
• Proper gloves (loose fitting), proper procedures,
  maintenance of transfer lines, awareness
• Proper gloves, proper procedure
• Establishment of controlled area, safety glasses
  face shield, proper procedures (pre-chilling)
• ODH training, proper use
• Monitoring and maintenance, proper location of
  dewars, ODH awareness

28
Liquid splatter vs. cold surface
Excerpt from ANL Cryogenic Safety Manual
29
Personal Protective Equipment (PPE)

• Safety glasses, face shield when cooling with
  exposed liquid or working with glass dewars
• Cryo gloves (inside sleeves), Lab coat and/or
  apron
• Long sleeves, pants, lab coat, no cuffs
• Proper shoes (no open toes no mesh fabrics no
  loafers)

30
Dewars
LN2
He
31
Anatomy of a typical He dewar

• Notice that all components hang from connections
  at the top
• Tipping and lateral shock can cause touches
  between different layers normally separated by
  vacuum
• Touches greatly increase the heat absorbed by the
  cryogens and their boil-off rate

32
Helium dewars
¼ lb relief (normally open)

• A hissing (gas venting from relief valve) dewar
  is normal when freshly filled or recently moved
• Continuous venting when undisturbed indicates
  breakdown of the vacuum barrier (softness)
  return dewar and think of ODH
• ¼ pound relief valves should always be open
  (sometimes they are shipped closed)
• Operator is exposed to vapor
• Rapid transfer or rapid venting can freeze valves
  and fittings
• Dunking transfer siphon or sample probe into LHe
  can cause vapor burn
• Pressure release after transfer can cause vapor
  burn

Vent (normally closed)
10 lb bursting disc
Siphon port
2 lb relief
Pressure gauge
Top view of a LHe dewar
33
Nitrogen dewars

• A hissing sound is normal if the dewar has been
  refilled
• External ice, sweating, or hissing of an
  undisturbed dewar indicates poor vacuum

• Operator is exposed to liquid and vapor
• Use gloves, identify the proper valve, turn it
  the proper direction

34
Transporting a dewar

• Do not push/pull from high above the center of
  gravity!
• Trip hazards exist for wheeled objects, too
• Do not rush
• Have you considered what hazards arise if the
  dewar tips over?

35
Whats safe? Whats unsafe?
36
Lesson learned (Accident at Univ. New South
Wales, Australia)

• Injury Lost use of hand for 10 days
• The principal cause of the INJURY was liquid
  nitrogen caught in the glove from severe
  splashing. The glove was not inside the sleeve of
  the coat.
• The person remembers that there was no immediate
  pain to the hand, only a sensation of numbness
  rather then coldness. An eyewitness estimates the
  duration of the exposure at 30 seconds only. The
  injury was then flushed with cold water for 20
  minutes (proper first aid).
• Contributing factors to the accident
• Crowded work area (another person's large dewar
  was in the way)
• Over-stretching to get around large dewar
• Turning the control valve for LN2 the wrong way
• Swapping hands for operating valve for LN2

• Lessons learned
• Wear gloves inside coat sleeves to prevent LN2
  entering gloves.
• Know which way to turn the control valve to stop
  the flow of LN2. (righty tighty, lefty loosy)
• Have a clear workplace Remove unnecessary dewars
  and equipment.
• Know where the cold-water tap is located inside
  the LN2 compound.

37
Gloves are mandatory
38
ODH rule of thumb (from Air Products)

• 10 liters of liquid nitrogen evaporated into an
  unventilated 16 x 16 x 8 foot room will reduce
  the oxygen level to 19.5
• Dewars that tip over or vent continuously in
  closed rooms or hallways could present a
  significant hazard if building ventilation failed
  
• (controls awareness, proper techniques,
  training)
• Dont transport open dewars in elevators
• The size of a 2-car garage, or 32 feet of
  hallway
• Onset of oxygen deficiency symptoms, and use
  of breathing apparatus for workers with prolonged
  exposure

39
Safety Information for Sealed Source Users
40
Sealed source
Sealed source Radioactive materials sealed
inside metal/plastic. Most sealed sources can be
handled without concern that the radioactive
material will be dispersed onto hands or clothing.
41
Sealed source
Types of sealed source
Plated
Activated metal
May be covered by Mylar, aluminum, steel or
plastic
wires
Foils
Capsules
Neutron Flux
42
Sealed source
Sealed sources are used
- in many laboratory devices, such as Radiation
counters, gas chromatographs, and portable
gauges.
- as check sources, calibration sources for the
detectors
43
Types of radiation
Alpha (a) Highly Energetic Helium Nucleus (42He)
Beta (b) Electrons
Gamma (g), X-ray (X) Electromagnetic Wave
Neutron(n) Neutrons
44
Alpha particles

• - 2 protons 2 neutrons
• 2e charge
• Massive Slow
• Typically emitted from heavy nuclides (Pu,
  U etc.)
• Travel only short distances (a few inches in
  air)

4
?
2
Example
238
234
4
?

Pu
U
94
92
2
45
Beta particles

• - Electron (positron)
• -e charge (e charge)
• Small particle
• High speed
• Energy distribution

Example
32
32
0
P
S

?
15
16
-1
46
Gamma-ray, X-ray

• - Electromagnetic wave
• No charge
• No mass
• Travels at the speed of light
• Very penetrating

Example
60
60
Co
Ni
? b
27
28
47
Neutrons

• - No charge
• Classified by energy Fast neutrons
  Thermal neutrons
• Produced through nuclear reactions
  (fission, excitation)

Example
10
11
2
1

Co
n
D
( B)
5
5
1
0
48
Sealed sources in 3113 3114
49
Units
Ci (Curie) Original Unit of radioactivity 1
Ci Activity of 1 g Ra 3.7 x 1010
dps (disintegration or decay per second)
1 mCi 10-3 Ci, 1 ? Ci 10-6 Ci Bq
(Becquerel) International Unit
1 Bq 1 decay per second
1 Ci 3.7 x 1010 Bq R (Roentgen) amount
of radiation required to create 1 esu (one
ionization) in 1 cm3 of dry air. rad (Radiation
Absorbed Dose) 1 rad 0.01 J/kg rem (Roentgen
Equivalent Man) rem rad x Relative Biological
Effectiveness 0.01 Seivert RBE for bs is 1.0
1.7
50
Exponential Decay
51
User responsibilities

• Authorized user
• Supervising activity using sealed source
• Assisting Leak test, Notify the RSO of any
  leak/damage
• Preparing Quarterly Report
• Ensuring Security
• Ensuring that all workers received appropriate
  training
• Notifying the RSO of any staff changes

• Radiation Workers
• Follow the instructions of authorized users
• Take required training

52
Survey Monitoring

• Be sure to monitor the work area while handling
  sealed sources.
• Select appropriate meters for monitoring.
• Alpha, low-energy Beta sources
• ? Scintillation survey meters (ZnS, CsI)
  Gas-flow counters,
• Silicon diodes
• High-energy Beta sources
• ? GM counters
• Gamma sources
• ? Scintillation survey meters (NaI)
• Neutron sources
• ? Neutron detectors (BF3), Proportional
  counters

53
Posting/Labeling
Door
sources
Cs-137 30 mCi T1/2 30.1y
Am-241 1 mCi Cs-137 8 mCi
Storage/case
54
ALARA
ALARA As low as reasonably achievable -
Radiation protection philosophy - Should be
applied to maintain any dose at levels as low
as are practicable
55
Protection
Time Shorter usage ? Less exposure Distance
Keep distance (Inverse square law) Shielding
Shielding material selection -
Bremsstrahlung
Monitoring Survey meter selection PPE
(Personal Protective Equipment)
gloves, glasses, lab coat, etc.
56
Time

• - Planning of experiment
• Cold run
• Written procedure

57
Distance
Distance is a large factor in reducing
exposure Inverse Square law When you double the
distance the exposure rate is decreased by
four Triple the distance? Half the
distance? Proper equipment (e.g. tongs)
58
Shielding
Select proper shielding material Gamma, X-ray
Thick/dense material
(e.g. lead, concrete, steel) Neutron Neutron
absorber (e.g. Paraffin) Beta Low Z material
(e.g. Plastic, wood, glass) Alpha No
shielding required(dead layer of skin cells is
shielding!)
Why not lead?? See next slide
59
Shielding - Bremsstrahlung
High Z materials (dense materials like lead,
steel) promote bremsstrahlung production (white
radiation emitted during braking of a charged
particle)
X-ray (Bremsstrahlung)
e-
Atom of shielding material
e-
60
Radiation Doses

• Typical Natural dose 0.24 rem/year
• Solar, radon, medical, etc.
• Maximum permissible occupational dose US NRC
  (radiation worker)
• Whole body 5 rem/year
• Extremities 50 rem/year
• Pregnant worker 0.5 rem total during
  gestation 0.05 rem/month
• UH regulations - Shield radioactive sources to
  less than 2 mR/hour at one foot. (ALARA)
• For b, 2 mrem/hour 0.002 rem/hour

61
Our beta sources

• Outside big plexiglass box 0.01 mR/hr 0.01
  mrem/hr (background level)
• For a 6 hour lab, 0.06 0.09 mrem
• At top surface of sealed source 1mR/hr. Hold
  it for 1 minute, 0.02 mrem
• At bottom (active) surface 15 mR/hr.Hold it
  for 1 minute, 0.25 mrem
• Keep bottom pointed away from people

62
Contact information

• In an emergency 911
• University of Houston Police Department (UHPD)
• [phone]
• Office of Environmental Health Risk Management
  (EHRM)
• [phone]
• (M-F, 730am 400pm) (After hours
  holidays, UHPD)
• Radiation Safety Officer
• [phone]