Lab Safety for Particle Experimentalists SLAC Course 110

1
Lab Safety for Particle ExperimentalistsSLAC
Course 110

• Martin Breidenbach
• June 2006
• December 2008
• January 2009

2
Lab Safety for Particle Experimentalists

• This is aimed at physics grad students and
  postdocs.
• The lab is the RD lab and not the accelerator
  or big detectors.
• No accelerator hazards e.g. Radiation or magnets
• The lab is not particularly dangerous you are
  more likely to be hurt in traffic at the entrance
  but there are hazards that many of us have
  learned about through close experience. The
  points here are offered to jump you over these.
  There is not, and cannot, be a prescription to
  avoid all risk. Thinking is requiredRisk can be
  intelligently managed!
• Many accidents are the result of a chain of
  errors or misjudgments. Reasonable precautions
  can make a single error inconsequential.
• I will avoid graphic illustrations of various
  accidents. However, the word horrible means
  exactly that. You would not want to see the
  pictures. When horrible is used, I mean it.

3
Disclaimers

• This talk is not a substitute for any required
  training. However, it does substitute for SLAC
  Course 251
• This talk is relatively dense and assumes you
  know basic physics.
• You and your line management are responsible for
  your safety. This talk is meant to expose you to
  some experience in a concentrated dose in the
  hope that you wont do again what many of us have
  learned by experience.

4
Topics

• Electrical
• Electronic
• Explosions
• Implosions
• O2 deficiency
• Lasers
• Chemistry
• Falls
• Radioactive Sources

5
Electrical Hazards

• Three routes to trouble
• Electroshock
• Arc Flash
• Reflex

6
Electroshock

• gt10 ma 60 Hz through the body is bad.
• let-go threshold 10-17 ma
• Chest paralysis (suffocation) 30 ma
• Cardiac fibrillation 75-100 ma
• Cardiac fibrillation need defibrillator in lt5
  minutes, preferably lt 2minutes. This level of
  shock unlikely but plausible in the lab. If there
  is an AED within running distance, its good to
  know where(There is an AED in Central Lab Annex,
  2nd floor, center corridor)
• Body resistance not really prdictable dry skin,
  lt50 V, resistance high
• Damaged or wet skin, 600 V, significantly lower
  resistance
• Neural damage, internal heating very bad. But
  this is not really a non-accelerator lab hazard
  at SLAC. Requires gross violation of electrical
  safety.
• If you or someone else gets shocked more than
  trivially, get professional help or call 911.

7
Arc Flash

• Electrical distribution system including 480
  VAC panels in labs can deliver enough current
  to make a horrible, continuous arc releasing
  substantial energy and radiation (i.e. an
  explosion) until some slow breaker opens. At 480,
  the arc will ionize air and Cu and just keep
  going. So Stay out of 480 circuits hot or cold.
  The required training, experience, and PPE to
  work safely is unlikely for almost all
  physicists.
• Example Consider a 480 V phase to phase fault
  with a current of 10,000 amps. This is 5 MW. If
  the upstream protection takes 10 cycles to open,
  this is 0.8 MJ. This is equivalent to 200 g TNT.
• Arc Flash hazard is divided into categories
  between 0 and 4, each with appropriate PPE. The
  PPE is rated by the incident energy it can take
  before the onset of 2nd degree burns.
• Arc Flash Hazard 1 PPE is rated at 4 Cal/cm2 (17
  J/cm2). Note that this is much less than sunlight
  for an hour because of the large UV component
  of the arc spectrum.
• Above Arc Flash Hazard 0 is for professionals!

8
Reflex

• Small shocks will cause an often large, more or
  less involuntary startle reaction. It can make
  you fall as in off a ladder or platform.
• This kind of shock is classic when debugging
  proportional chambers, drift chambers, etc. The
  current and stored energy are usually too low to
  be an electroshock hazard. Think about where a
  startle reaction might take you!

9
Reasonable Electrical Practice

• Stay out of 480 circuits. ( note the period. Just
  stay out!!!) (breaker operation exception
  described next slide)
• Stay out of 208/120 3f panels-(breaker operation
  exception next slide)
• Wiring a (disconnected!) chassis
• Know the standard electrical color code
• Black (or possibly red or blue) is hot
• White is neutral
• Green is ground.
• If, for some bizarre reason, you are forced to
  use cable that does not conform, use properly
  colored shrink tube or colored tape to identify
  the wires.
• Insulate the chassis connections so you cannot
  touch them when you debug your work. RTV glob is
  the minimal acceptable insulation. Fiberglass
  covers are better.

10
Breaker and Disconnect Switch Operation

• Occasionally it may be necessary to open or close
  circuit breakers or switched disconnects.
• It is reasonable for you to operate these devices
  at SLAC if all of the following conditions are
  satisfied
• The NFPA70E Arc Flash Hazard Rating is 0 or -1.
• The voltage is 480 V or less.
• You are wearing appropriate PPE.
• If you are closing a breaker, you reasonably
  understand why it was open.
• No other jurisdiction forbids it (e.g. you are
  not at SLAC).
• More details
• NFPA70E is the counterpart document to the
  National Electrical Code that deals with
  operations as opposed to construction standards.
  It specifies hazards associated with various
  equipment configurations.
• In this context, operation of a circuit breaker
  or switch with covers on is permissible if Arc
  Flash Hazard 0 (and in probably rare cases of lt10
  KA short circuit current, Arc Flash Hazard -1).
• Panels at SLAC should be labeled with their Arc
  Flash rating for covers on and off.

11

• Most 115-208 V panels are Arc Flash Hazard 0. In
  rare cases, they may be Class 1.
• Personal Protective Equipment
• For Arc Flash Hazard 0
• You wear safety glasses.
• You wear cotton (or non-synthetic) long sleeved
  shirt.
• You wear cotton (or non-synthetic) long pants.
• Technique when operating a breaker or switch,
  stand to the side close to the wall and look
  away. If there should be an arc, you wont get it
  in the face.
• Reasonableness If a 15 or 20 Ampere 115 or 208 V
  breaker tripped because of an overload that is
  understood and corrected, resetting is
  reasonable. If a 480 V breaker tripped
  mysteriously, leave it to an electrician.
• Some equipment, such as welders, connect with
  plugs and sockets that are mechanically
  interlocked so that the plug can not be inserted
  or removed with the switch on. Ensure that the
  equipment is off before operating the switch.
  (Some older sockets do not have this interlock,
  again ensure that the equipment is off before
  inserting or removing the plug.)

12
Clean Room Issues

• There are many clean rooms in use e.g. EXO, Si
  Lab, and GLAST. Clean room clothing may be a
  problem for some activities Electrical switching
  and TIG welding are the two prime examples.
• PPA has tested the Tyvek clean room suits, and
  they are reasonably ok. (The nylon zipper will
  burn, but the Tyvek does not)
• Nitrile gloves burn sufficiently to be a clear
  hazard.
• We have not found an elegant solution for a
  clean, reasonably non-flammable glove.
• The working solution is a deerskin welding glove
  under nitrile gloves.
• The search continues for something better.
• Remember that welding requires a fire watch
  person with a CO2 extinguisher.

13
Sidebar SLAC Electrical Power Distribution

• The overhead transmission lines coming down from
  Skyline are 230 KV 3 f with a capacity of 100
  MW.
• The Master Sub has transformers taking the 230 KV
  to 12.6 KV for distribution around the site.
• 60 KV lines come in from campus and are used when
  the 230 KV line is unavailable.
• Substations usually reduce the distribution
  voltage to 480 V to panels in buildings.
• Smaller transformers take the 480 V to 208 V.
• Breaker panels are used to distribute these
  voltages.
• Again Stay out of the lab power distribution
  system!!!

In a 3 f system, the stated voltage refers to the
line to line voltage. The line to neutral voltage
is down 1/v3. So the standard 120 V is line to
neutral of a 208 system. The system is often
referred to as 208/120 Volts.
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Electrical Issues

• It requires a lot of paperwork to work hot on a
  chassis with exposed 120 VAC and it is an
  unnecessary risk, so insulate those connections
  to the power supply.
• Grounding limits the potential of a (conductive)
  device with a fault to (assumed grounded) you. A
  ground is effective only if it can carry enough
  current to trip a breaker and/or reduce the
  potential to non-hazardous levels.
• It in a worst case fault, the impedance of the
  ground connection should keep anything you might
  be touching below 50V to ground!) Assume you can
  get 100 amps out of a wall panel before a small
  breaker opens. Then you need lt 0.5 ? to a solid
  ground.

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Sidebar - GFI

• A Ground Fault Interrupter (GFI) compares the
  current on the hot and neutral by running both
  through a toroid transformer and amplifying the
  difference. An imbalance of 4 to 6 ma triggers
  the spring mechanism of the breaker (or outlet).
  A GFI breaker has no ground connection! (A GFI
  outlet has a ground connection for the 3 wire
  cord.)
• Note that 100V x 10 amp x 5 mS 5J, which will
  hurt. However, 10 amp through you is unlikely (at
  115 V), unless you are in salt water.)

16
Grounding
Typical SLAC configuration 480 V Building
distribution system feeds 480 V to 208/115 V
transformer to breaker panel. (Typical
residential configuration 230 volt single phase
center tapped pole transformer feeds a breaker
panel) The center tap connects to the neutral
bus, and is grounded at the panel. There is
usually a separate ground bus. Note that the
motor frame, or in general, any accessible
conducting parts of a device are connected to the
ground wire. Double insulated devices are
considered safe enough not to have a ground
connection.
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Grounding Current flow during a short
Note the short from the hot side of the motor
winding to the frame. If the short impedance is
low enough, enough current (dashed lines) will
flow as shown to trip the breaker. In any case,
the impedance of the ground wire should be low
enough to keep the potential difference between
the frame and building ground below dangerous
levels (50V). The same strategy applies to most
laboratory equipment, where the ground conductor
system must be adequate to keep the frame
potential below 50 V.
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Wire Sizes
Wire must be sized to prevent excessive heating
and voltage drop. Reasonable practice with
insulated wire is in table. Voltage drop 5
usually considered ok but note 20 amperes in
12 wire is 30 meters (out and back). Use
proper extensions! The rule of thumb is 12 for
20 amperes, 14 for 15 amperes, and 16 for 10
amperes. However long extensions may need heavier
wire. Calculate for a 5 voltage drop or less. Do
not daisy chain extensions.
AWG Wire Size (solid) Diameter (inches) Resistance (Ohms/Km) Nominal Current Capacity (Amperes), Insulated Cable
18 0.0403 20.9 5
16 0.0508 13.2 10
14 0.0640 8.28 15
12 0.0808 5.21 20
10 0.1019 3.28 30
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Non Contact Voltage Detector

• These inexpensive devices (10-20) capacitively
  sense AC voltages. All do 115V, 60 Hz AC, and
  some do 24 VAC. Very useful for homework!
• The sensors do not detect DC, and may not be used
  at SLAC as verification of the zero voltage state.

20
Capacitors store Energy

• Doorknob capacitors
• Ceramic dielectrics such as Strontium Titanate
  give 2.7 nF _at_30 KV or 1 J (Nasty) in a device
  2 3/8 x 7/8

Pulse Capacitors 100 µF _at_ 2KV or 200 J Totally
deadly Device size 3 ¾ x 4 ½ x 7 3/4
Large Capacitors should be shorted when not in
use Bleeder resistors should not be trusted to
discharge a capacitor. You need more training to
work with large pulsers.
21
Electrical Limits

• There is a variety of advice on what is
  dangerous
• SLAC EHS Manual Chapter 8
• NFPA 70E National Fire Protection Agency
• DOE Electrical Safety Orders
• Below 50 V is ok.
• There is serious burn hazard with high current
  supplies at even a few volts. Car batteries can
  deliver 400 Amps without blinking. So that neat
  ring can dissipate 4 KW and amputate a finger
  painfully and quickly. Experienced people remove
  jewelry around car batteries and VME (or Fastbus)
  power supplies.
• Some sources claim stored (capacitive) energy gt
  10 J (below 50 V) is a hazard. Most of us are
  more excited about the burn possibilities of
  supplies that can deliver more than 10 Amp

22
Electrical Limits. continued

• Above 50 V
• Below 5 ma power supply capability you cant
  fry yourself. But you can jump.
• The 10 J limit is becoming very real!
• Below 250 V its hard to electrically puncture
  the skin, so the body impedance makes it hard to
  deliver 10 J. Note that this is for a dry, intact
  body! By 500 V, its only what the circuit can
  deliver. Believe!
• At high voltage, you will probably survive 10 J,
  but you will remember it until Alzheimers takes
  over. Be real careful when theres more than 1 J.

23
Sidebar Control of Hazardous Energy

• Formerly known as LOTO Lock Out Tag Out
• Work on de-energized equipment connected to wall
  (no plug to pull) by COHE procedures. This is
  hardly ever for physicists. But its good to
  understand the issues
• The idea is that upstream disconnects (breakers,
  knife switches, fuses) must be open. And locked
  open. And tagged with lockers name etc. Theres
  a course on this.
• But how do you know you got the right breaker?
  Sometimes its obvious, but often the panel is far
  away, and there is no visible conduit from the
  load to the breaker. So you measure the voltage.
  Thats hot work. And that requires PPE for
  anything that might go wrong like using a bad
  meter that presents a low impedance to the bus
  (and a horrible arc). And you need a Hot Work
  Permit. Which PPA has never granted at least in
  the last several years. So Fugeddahaboutit.

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Electronics

• Most modern signal processing electronics from
  charge amplifiers through computing are
  harmless. You can diagnose the circuit being
  reasonably confident that you are far more likely
  to blow up the FET through Electrostatic
  Discharge (ESD) than it is to tickle you.
• When you change boards in your computer, turn it
  off but leave the AC connected. If you are not
  using an ESD wrist strap, hold the board in one
  hand and touch the cabinet with the other before
  inserting board. Etc.
• Silicon detectors may have bias supplies up to
  500 V (for high radiation damage environments).
  Its rare that the supply can deliver 5 mA. Its
  almost weird that the stored energy could
  approach 10 J. Special precautions are needed,
  including paperwork, if the supply can deliver
  more than 5 mA.
• Photomultipliers operate at 2-3KV. There are many
  older bulk supplies designed to power many
  PMTs that can deliver 20 mA or more. These are
  serious supplies. Almost always, the HV is
  delivered in co-ax (RG-59), and the co-ax is
  terminated with modern HV connectors (MHV,
  Reynolds) that make it exceedingly difficult to
  accidentally contact the HV. However If you need
  to debug a PMT base, use a NIM bin Power Supply
  that has a max current of 1 mA or less.
• Avoid adapter cables that change HV connectors
  into non-HV connectors, and especially forget HV
  cables that have alligator clips on the ends.
  They are called suicide cords for a reason!

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Electronics Technique, basic!

• Remember to turn off the HV before sticking your
  hands inside. (Remove plug or lock off the
  equipment if not cord-connected).
• Remember to discharge capacitors
• Use proper grounding. The grounding of a PMT base
  or LST or most other detectors than Si are
  usually through the HV co-ax.
• Be particularly careful if you have to work in
  the dark e.g. searching for light leaks for PMT
  or APD based counters.
• This comment sounds simple, but it isnt. EXO
  refrigerators and compressors are connected with
  very expensive plugs and sockets to avoid locking
  issues!!

26
Sidebar RG59

• Note that the capacitance of most random co-ax is
  100pF/foot. You can easily destroy electronics
  with a disconnected cable that charges up to a
  few KV. For higher HV, a charged cable is
  dangerous. (100 ft _at_100 KV 50 J)
• The dielectric in most co-ax is polyethylene.
  Poly is a good dielectric, but its chemically
  close to napalm. A few cables in the lab are no
  problem, but a rack full is a serious issue. SLAC
  has had two(!!) serious fires that started from
  minor arcing in co-ax. The SPEAR 1 SLAC-LBL
  Magnetic Detector (aka Mark I) had spark
  chambers. In the 70s, the pulsers ignited a very
  exciting fire. Aluminum racks melted. Months of
  work to rebuild. In the 90s, ion pump HV cables
  started a cable fire in the SLC e- damping ring.
  Again, a major mess and months of expensive
  recovery. Bromated polyethylene or teflon
  dielectric is a little more expensive, but much
  safer

27
Electronics, continued

• Laser supplies are serious. The flashlamp
  supplies often break the 10 J limit. If you open
  laser enclosures, you need laser safety training,
  but remember the HV basics
• The power supply should be disconnected from the
  wall
• The energy storage capacitor should be grounded
  with a ground hook.
• A SLAC laser will (most likely??) have stored
  energy far below 1 KJ.
• A simple ground hook without a series resistor is
  acceptable.
• Two ground hooks are needed to discharge
  floating capacitors.
• Supplies for Pockels Cells can be hefty.
• There are occasionally high voltage low impedance
  operational amplifiers (Trek) that are lethal. No
  hot work on these guys, and make sure the load is
  enclosed.

28
Electronics Techniques

• On occasion, it is necessary to debug a circuit
  that can hurt. If it has gt 50 V and (5 mA or 10
  J), there are hot work (energized circuit
  )requirements permits and non-routine JHAMs.
  But there are seatbelts for this car
• Make sure you are floating at high impedance to
  ground. A dielectric mat on the floor, or dry
  wood for a few 100V is good. ESD wrist straps
  are relatively high impedance, so delicate
  components are protected but you are not
  grounded.
• Use one hand. If you touch something, make sure
  it will be finger to wrist or less. Pull your
  hand out of the chassis when adjusting the scope.
  Eliminate the potential of a hand to hand or hand
  to foot shock. And what is the chair made of?
• Think about what will happen if you are (very)
  startled by a shock.

29
High Voltage Connectors
Reynolds 10 KV
Note non-recessed pin. Use for low level signals
only!
SHV 5 KV
BNC 500 V
30
Miniature Connectors
Note recessed pin
Lemo HV 1500 V
Standard Lemo Signal only
31
More Electronics Advice

• If its gt50 V, make sure somebody else is around.
  This is particularly true if you are debugging a
  drift chamber in the detector!
• If you get zapped, get checked out by medical.
  Too bad that you are embarrassed, dont make it
  worse.
• Might be a good idea to take that CPR course, and
  know where the AED is.

32
Explosions

• Explosions are all about stored energy In the
  lab the prime suspect is the gas bottle. The
  standard K bottle is 200 SCF at a pressure of
  2200 PSI. Or V42 liters and P 147 Bar 15x106
  Pascal
• UPV/(?-1) (for expansion to 1 bar) where
  ?Cp/Cv
• U0.9 MJ for a monatomic gas (e.g. helium or
  argon), U greater for nitrogen, oxygen, CO2.
• Scale 1 gram of TNT 4. 2 KJ
• So gas bottle is ¼ Kg TNT!!!!
• (For reference, a jelly donut is 200 Calories
  (note those food calories are Kcal 0.8 MJ, but
  at least jelly donuts dont explode rapidly)
• Breaking the valve stem of a gas bottle is a big
  deal. Its a deadly rocket. Handle bottles
  carefully!
• They must have their valve cover on when not in
  use.
• They must be strapped to a solid support at two
  heights to prevent tipping.
• They must have a proper regulator to control the
  output pressure.
• Wear safety glasses if there is any possibility
  of a gas jet to your face!!

33
Gas Bottles, continued.

• Gas bottles valves often have different threads
  to prevent inappropriate regulator use. For
  example, O2 regulators and pressure gauges and
  plumbing must be oil free. Be sure the regulator
  is correct, and dont force the threads!
  Flammable gas bottles usually have left-handed
  threads.
• Occasionally there are even higher pressure
  bottles. EXO uses 6000 PSI argon for
  Joule-Thompson refrigeration. These bottles have
  their own special regulators.
• Some gases burn or explode. There is a very
  strong trend to use non-flammable gases for bulk
  applications such as the Babar LSTs. However,
  isobutane often is a component of these gases,
  and might be used when developing a mixture.
  Hazardous gas detectors are used where there is a
  chance of a leak. These detectors are installed
  and maintained by EFD. They warn at a modest
  fraction of the Lower Explosive Limit (LEL) and
  must be heeded. Horrible accidents have happened
  to HEP experimentalists with flammable chamber
  gases.

34
Cryogenic Fluids

• Cryogenic liquids expand when they warm up.
• Argon at STP is x860 liquid volume
• Xenon at STP is x550 liquid volume
• Nitrogen at STP is x710 liquid volume
• If a cryogenic liquid warms up, the pressure will
  increase. In a properly designed system, the
  volume of liquid is limited so that the warm
  system can handle the pressure. In addition,
  there should be relief valves and/or burst disks
  on any plumbing segment which can be isolated by
  the valves. Very few pressure systems can handle
  more than 2000 PSI, most much less. Weak links
  are usually windows, bellows, and feedthroughs.
• Simple safety principle for cryogenically
  recovering a gas into a pressure bottle e.g.
  recovering xenon Never dunk a recovery cylinder
  in liquid nitrogen for more than half its length.
• Wear safety glasses.
• Use cryogenic rated gloves when pouring LN. Dont
  spill LN into your shoes! Cryogenic burns are
  serious.
• Cryogenic fluids can cause oxygen deficiency
  hazards as they vaporize. Ensure good lab
  ventilation when using LN for cooling. Be aware
  of the potential for nanoclimates e.g. your
  head under a light blocking cloth.

35
Implosions

• PMTs - Work in the lab may involve large
  photomultiplier tubes. The tubes are made of
  relatively thin glass, and are evacuated.
  Breaking them causes glass to be projected with
  high velocity. In certain situations, the shock
  wave from an imploding tube can trigger adjacent
  tubes. Always use goggles or safety glasses when
  handling these tubes. And these PMTs are
  typically quite expensive!
• Thin Windows Large thin windows for vacuum
  systems are rare in the RD lab but common around
  accelerators. If the window was aggressively
  designed to limit multiple scattering, it can be
  quite delicate and the shock wave from an
  implosion is serious. On most lab scale
  apparatus, breaking a window will only take out
  equipment

36
O2 Deficiency
As the partial pressure of O2 drops, so does
arterial O2 saturation. Judgment may be impaired
first, but loss of consciousness occurs without
warning.
37
O2 Deficiency

• Normal air is 21 O2. Most O2 deficiency
  monitors alarm at 19.
• When working with cryogenic fluids, O2 deficiency
  can be a hazard if there is a spill. Remember
  that volume change of 700.
• Example The SLD calorimeter had 50,000 liters of
  liquid argon. In a worst case (but inconceivable)
  spill, the heavier than air argon expands by x
  860 and produces enough gas to fill the full CEH
  pit almost twice!
• If there is a large spill get out! A 200 liter
  LN dewar holds a quite serious amount of gas.
• Labs where there is a potential for a leak or a
  spill should be equipped with O2 deficiency
  monitors. These should give early warning and
  summon the Fire Department.
• In a small space, it is easy to displace enough
  air to be dangerous. O2 deficiency is perhaps the
  major hazard of Confined Spaces, and a special
  permit and training is required to enter a
  Confined Space.

38
Lasers

• Some of the lasers in the lab have sufficient
  power to permanently damage the retina.
• Further, UV and IR lasers cant be seen and can
  do damage.
• The primary level of control is containment
  there should be no laser light scattering around
  the lab from Class IIIb or IV lasers. Some lasers
  contain the beam in optical fibers with proper
  light tight terminations at both ends. Never
  operate these lasers with the fiber removed (at
  either end!) in a non laser-safe lab.
• Advanced training is required for work with these
  lasers. Laser goggles must be selected for the
  particular laser one size does not fit all.

39
Sidebar - Laser Classifications (Loosely)

• Class I
• Cannot cause eye damage either because lt0.4 µW CW
  visible or completely enclosed. Note that if the
  enclosure is breached, controls for the native
  laser power class are required. CD players, laser
  printers, etc
• Class II
• Cannot cause eye damage during the aversion
  response (0.25 sec) (aka blinking). Only visible
  (400-700 nm) 0.4 µW lt P lt 1 mW (CW). Usually
  He-Ne lasers, laser pointers, range finders, etc
• Class IIIa
• Cannot cause eye damage during aversion response.
  Injury possible with optics or staring into beam.
  Visible, 1 mW lt P lt 5mW CW. Laser pointers, laser
  scanners, etc
• Class IIIb
• Can cause injuries from viewing direct beam or
  specular reflection. 5 mW lt P lt 500 mW CW.
  Diffuse reflection will not cause injury unless
  light collected by optics. Spectrometry sources,
  etc. Eye protection required.
• Class IV
• Primary beam, specular and diffuse reflections
  can injure eyes and skin. Also can ignite
  flammable material. All wavelengths with P gt 500
  mW. All pulsed lasers that the eye can focus (400
  nm 1400 nm). Significant controls and eye
  protection required.

40
Chemistry

• This is not a general chemical hazards review,
  but a few special cases that come up often. Use
  appropriate precautions and PPE. Material Safety
  Data Sheets (MSDSs) should be first order check.
• Cleaning
• Ethanol and acetone are often used for cleaning
  UHV and other components. Both are serious
  inhalation, transpiration, and fire hazards.
  Ensure good ventilation. A vapor hood is required
  if the quantities approach a liter.
• Make sure you know a fire extinguisher location.
• For quantities more than a squeeze bottle squirt,
  wear appropriate gloves.
• Epoxies
• The unreacted components of many epoxies are
  quite irritating. Wear nitrile gloves.
• Scintillation Phosphors Occasional use is made
  of organic scintillators in their raw form. These
  chemicals may be toxic. Check the MSDS!
• Some chemicals (perhaps unlikely that you will
  encounter them) absolutely need special training
  and facilities
• Dangerous liquids e.g. Be solutions, HF
• Dangerous gases e.g. Arsine, Chlorine, Bromine
• Forget about it e.g. Methyl Mercury

41
Vacuum Systems
                                                              

• Laboratory UHV systems may be pumped with
  turbopumps or ionpumps.
• Turbopumps are somewhat delicate, but present few
  personnel hazards.
• Ion pumps are reliable, moderate cost devices but
  operate at substantial voltage levels. (The
  controller shown here will put out 3 KV at 7 ma.)
• The HV cables of modern pumps are reliable and
  safe, and some modern controllers shut down when
  the cable is disconnected. In general, there
  should be an independent ground connection
  between the supply and the vacuum plumbing, and
  the supply should be turned off before
  disconnecting the cable.

                      
42
Vacuum System Baking

• Metal vacuum systems often need to be baked to
  drive off water and other contaminants.
  Temperatures may be as low as 75 C for delicate
  internals, and up to 400 C for a serious bake.

• Heating is often done with Heating Tapes, glass
  insulated resistance wire.
• Do not exceed the tape temperature rating.
• Make sure the controller includes a GFI.
• Ground the vacuum system. Variacs are often used
  to control the voltage to the heaters. Note that
  Variacs are not transformers, and do not isolate
  the line.
• Make sure the stainless is substantially (openly
  obvious to a casual observer) grounded.
• Check for fire hazards.
• Be aware of burn hazards!

43
Falls

• Strangely enough, slips, trips and falls are the
  most likely accidents. Falls can be quite
  serious.
• In the lab, there may well be A ladders, but
  extension ladders and scaffolding are unlikely.
  (Not the case near a detector)
• The classic ladder accidents
• Going on or above the penultimate step of an A
  ladder.
• Using the top half of an extension ladder by
  itself.
• Try to tie extension ladders so they cant slip.
• Think about the surface supporting the ladder!
• Dont over-reach. Bad things happen when the
  Center of Gravity is not over the base. Get down
  and move the ladder instead.
• Fall protection or barriers are required on
  elevated work surfaces.
• Be particularly careful of situations where the
  involuntary reaction to a (small) shock can
  initiate a fall.

44
Radioactive Sources

• It is assumed that you have some knowledge of
  nuclear physicsand that we will not talk here
  about accelerators or accelerator induced
  radioactivity.
• Types of sources
• a particles have no range and are stopped by the
  skin (unless they get inside)
• ßs ionize immediately, but usually do not have
  the range to do damage.
• ?s go some distance before Compton scattering or
  photoelectric effect kicks out an e- which
  ionizes internally.
• Most lab sources are modest hazards if they are
  not ingested or inhaled, usually meaning they are
  sealed
• Nanocuries to microcuries should not be carried
  in your pocket.
• 100 microcuries is a serious source, but still
  can be handled in the lab.
• Millicuries and above need help from Operation
  Health Physics.
• Occasionally an unsealed source is needed when
  the recoil nuclei are of interest, or a liquid
  solution is needed to, for example, electroplate
  a source. Special handling procedures are
  required, and OHP must be brought in.
• For approximate point sources, dose will go
  1/r2. Even smaller sources can cause unwanted
  doses as r gets small

45
Sidebar Units1

• SI units are recommended, but not yet in common
  use.
• Unit of Activity Bequerel 1 Bq 1
  disintegration/sec
• The Curie (Ci) 3.7x1010 Bq
• Unit of absorbed dose Gray 1 Gy 1 joule/Kg
• 1 Gy 100 rad (There are lots of survey meters
  around calibrated in rads, and occasionally even
  the (obsolete) Roentgen.
• The Roentgen (R) measures the charge produced by
  ?s showering in air. 1 R 2.58x10-4 coul/Kg
• Unit of equivalent dose Sievert 1 Sv 1 Gy x
  wR
• wR radiation weighting factor (was Q quality
  factor in oldspeak)
• wR 1 X and ? rays, all energies
• wR 1 electrons and muons, all energies
• wR 20 alphas
• The old unit is the REM 1 Sv 100 REM
• 1 Mainly taken from Review of Particle Physics
  (2004)

46
Radiation Scales1

• Recommended limits for Radiation Workers
• CERN 15 mSv/year
• U.S. 50 mSv/year
• SLAC 15 mSv/year
• Lethal dose (LD50, no medical treatment) 2.5
  3.0 Gy
• Natural background 0.4 4 mSv/year
• Flux to deliver 1 Gy 6.24x109/(dE/dX) charged
  particles/cm2
• So it should be obvious now why a Ci is a big
  source.
• It is assumed that you have GERT (General
  Employee Radiation Training) . It is possible but
  unlikely that you will need RWT1 training. RWT2
  training is for contaminated locations not our
  labs!
• 1 Mainly taken from Review of Particle Physics
  (2004)

47
Coda

• SLACs PPA Safety Officers are Frank ONeill, Joe
  Kenny and Sandy Pierson
• They may not know the answer to all your safety
  questions, but they usually can provide good
  pointers. Talk to them!
• Think!
• If there is a problem requiring emergency help
  call 911 from a SLAC phone, or 911 from a cell
  phone (assuming there is a signal). You will need
  to describe your location - obvious, but do you
  know the Building Number?