Hoods

1
Hoods

• Control toxic/offensive/flammable
  vapors/gases/aerosols.
• Preventinhalation exposure in the laboratory.

2
How a hood works
There is a fan up above, usually at the roof or
attic, pulling this air up, 400 - 1200 ft3/min

• Hood is a ventilated box
• Know these parts

sash
baffle
face
bypass grill
monitor
airfoil
exhaust
3
Simple Exhaust Calculation

• Simplest hood

• No bypass grill, just exhausted enclosure

• typical -- vertical sash, width of 5 ft, open 18

5 x 1.5 7.5 ft2

• fan is set to pull a constant 750 ft3/min

• Calculated face velocity

(750 ft3/min)
_________
100 ft/min

7.5 ft2
4
Same hood, sash pulled down

• Sash opening now 3" high, face is 1.25 ft2

• Fan strains to pull 750cfm through 1.25 ft2 (600
  ft/min), very high air speed develops in opening,
  playing havoc with small items and hood liners.

5 x 0.25 1.25 ft2

• The bypass grill hood was developed to alleviate
  this problem.

5
Bypass grill function

• air allowed in through bypass WHEN THE SASH IS
  DOWN.

• When sash is up, bypass grill is blocked, the air
  is drawn into the face

6
Hood Side View

• Bypass grill hood design still very common.
• Volume velocity of exhaust is constant, set to
  maintain linear speed between 80 and 125 ft/min
  at face, at a certain sash height.
• When sash lowered, air is pulled through the
  bypass, prevents excessive air speed under the
  bottom of the sash.

7
Variable Air Volume (VAV)
The sash height or face opening controls a damper
or the fan speed.

• Sash up increased exhaust volume rate.

• Sash lowered, volume velocityreduced.

• Sash down minimal exhaust necessary.

• Energy is conserved and face velocity is kept
  relatively constant regardless of sash height

8
Sash counterweight

• This is a hood in storage. Slightly used, in
  good shape.

• This is the back of it. The sash weight feels
  like about 15 kg.

• This is the sash weight lowered (sash is up).

9
Sash weight cables/pulleys
10
Cable/pulley schematic

• Sash down (weight up).

• Sash up (weight down).

• When movement becomes difficult, it means the
  cables or pulleys need attention. CALL SOMEONE.

• Dont put your head in the hood. (For a couple
  of reasons.)

11
Containment and the 6 line

• The barrier provided by the hood face is fragile.
• Demo this yourself with dry ice water
• Keep all work behind the 6-inch line. (Its
  about 15 cm.)

demo video
12
(No Transcript)
13
Autoclaves

• rather quickly

14
Autoclaves

• Autoclave is strong vessel in which water heated
  under pressure. (Recall that bp is higher at
  higher pressure.) Superheated steam?
• Commonly 18 psig and 250oF.
• Sterilize instruments, media,and infectious
  waste.
• ...and other activities

other liquids may be used in chemical reactors,
also called autoclaves
15
Hazards

• Burns -- steam, hot water.
• Inadequate killing of infectious organisms.
• Pressurizing rupture of closed vessels inside
  autoclave or on opening of door.

16
Preparation

• Clear drain screen to allow steam circulation.
• Arrange load to allow steam circulation.
• Check door gasket for damage.
• Use secondary containment with liquids and
  infectious waste.
• Use only borosilicate (pyrex type) glass.
• Loosen caps or use foil covers or cotton plugs.
• Do not overfill containers.

17
Set and Start Autoclave

• Thirty minutes is MINIMUM.
• Time required is load dependent.
• Make sure everything is in completely.
• Tighten door properly.
• Start cycle.

18
And then

• NEVER try to open while its operating.
• Wear heat resistant gloves, splash goggles.
• Check pressure gauge 0 psi before opening.
• If theres resistance, do not force.
• Stand back.
• Open door 1/2 inch, allow steam to dissipate.
• Slowly open door further.

19
Opening Door Too Quickly

• Can cause even Pyrex containers to crack
  (spilling/splashing very hot liquid)
• Can cause rapid violent boiling of liquids
  because they are higher than bp now.
• If load became unstable, items might fall over
  or fall out and splash/spill.
• If inner container has been pressurized
  (inadvertently) it may burst.

20
Last remarks

• Be trained.
• Be careful.
• Do not make repairs to the autoclave.
• Autoclave testkits availablefrom REM.

21

• And the next equipment safety topic is..

22
Centrifuge Safety
23
Centrifuge defined

• A mechanical device that uses the principle of
  centrifugal force to separate materials of
  different densities.

24
Centrifuge at NASA Ames Research Center.
Featured in movie Space Cowboys, 2000
25
Urania Observatory, The Netherlands
26
UC Davis Engineering
27
RPI Earthquake Engineering
28
The centrifuges in this lesson are

• HIGH SPEED centrifugesaka SUPERSPEED centrifuges
• and
• ULTRA centrifuges

up to around 22,000 rpm
ultra higher. Modern ultras have max speeds
80,000 150,000 rpm
29
They can look a lot alike.

• (high speed and ultraspeed centrifuges, that is.)

From Western Michigan Biology teaching
labs Ultraspeed centrifuge High speed
centrifuge (and a -80 freezer)
30
They can look a lot alike.

• From somewhere in Korea

31
Micro or bench top high speed

• These are not the same as high speed
  centrifuges, not as fast (around 5,000 13,000
  RPM)
• Still serious safety considerations, but the
  incredible stress of gt16,000 RPM is not one.
• Read the owners manual and follow the safety
  guidance given there.

32
High speed centrifuge

• Beckman Avanti J series
• 26,000 rpm (revolutions per minute)
• 82,000 g (gravities)
• Weight 600 lb

33
Ultracentrifuge

• Beckman OptimaLXP
• 100,000 rpm
• 802,400 g
• Weight 1025 lb

34
Ultracentrifuge

• Sorvall Ultra-Pro 80
• 80,000 rpm
• 602,644 g
• ??? lb

35
Micro-ultracentrifuge

• Sorval M150 SE
• 150,000 rpm
• 1,048,000 g
• ??? lb (fairly small unit)

36
(No Transcript)
37
The centrifuge component
voted most likely to maim or kill is .. THE
ROTOR.
38
Rotors

• Fixed angle rotor

Rotor (high speed or ultra) is 10 - 30 lb piece
of metal or composite, carefully designed and
fashioned to turn smoothly and withstand the
incredible forces concomitant with spin speeds of
15,000 - 150,000 rpm.

• Swinging bucket rotor

39
Care and Attention

• Safe high-speed spin requires nearly perfectly
  balanced load.
• Age, use, and misuse contribute to rotor flaws.
• A rotor which comes apart at high speed can be
  deadly.

40
Primary hazards

• Mechanical failure

• Dispersion of aerosols
• (hazardous aerosols)

41
Mechanical Failure

• Is caused by age and/or by improper use and/or
  inadequate care...
• of centrifuge or rotor.
• (Especially the rotor.)

42
Tiny flaws are
NOT so tiny at 80,000 rpm
These are micro-fissures and cracks caused by
stress and corrosion in the bottom of a tube
cavity.
43
(Purdue 2003) This rotor came apart while coming
up to speed (not yet spinning at full speed)
The 6 inch (15 cm) long chunk damaged (ruined)
but did not completely penetrate the centrifuge
lid and housing. The motor and spindle were also
destroyed.
44
(MIT 1999) This rotor split in half at 55,000 rpm
after 3 h of what was supposed to be a much
longer spin.
Grad student report Rotor was manufactured in
1986 and was covered for 10,000 hours of
operation or 5 years, whichever comes first. No
surprise that it flew apart 13 years later.
Fortunately the centrifuge housing contained it.
45

• (Cornell, 1998)
• The rotor failure was not contained.
• Much other damage done, equipment ruined,
  chemicals spilled.
• Nobody was near, or someone would have been badly
  hurt or killed.

46
To reduce wear and chance of failure

• Follow instructions in manual and rotor care
  guide
• Use only compatible rotors
• Check routinely for rotor damage
• Don't overfill tubes
• Cap tubes
• Balance load carefully
• Check that rotor correctly seated on drive
  spindle
• Run at lt max safe speed
• continued

47
To reduce wear and chance of failure, continued

• Stay right there until full speed is reached.
• Stop the centrifuge if anything seems unusual
• Never open until stopped (never manual brake)
• Clean rotor gently
• Dry completely
• Store rotor upside down (why?)
• Maintain a careful rotor log
• Derate and retire rotors for age/use

48
To minimize aerosols and risk of exposure

• Most points on preceding panel, PLUS
• SOPs for human or infectious centrifuge samples
  should address this issue carefully
• Know and follow emergency procedures.
• See handout.

49
Chances are very small of reaching this slide
before 1120.THE END