Download Your Magnet Safety Team - Center for In Vivo Microscopy

Magnet Safety Training
Center for In Vivo Microscopy
V1.4
Updated: May 15, 2012
Your Magnet Safety Team
Larry Hedlund
Gary Cofer
Bastiaan Driehuys
General MRI Hazards
• An MRI scanner creates a magnetic field that is 30,000-150,000
times stronger than the earth’s magnetic field and is always on
• While hazards to people with pace-makers and implants tend to
be emphasized, projectile hazards are most worrisome for us
• Within a few feet of the magnet, the field gradient can rip steel
objects out of your hand
• The onset of this zone is very rapid and non-linear
• Objects can reach speeds of 80mph before slamming into the
magnet (or you)
Center for
In Vivo
Microscopy
NCRR
Unique Issues to CIVM
Compared to other magnet facilities like:
• A clinical 1.5T MRI suite
• An NMR spectroscopy facility
• We have the following differences:
• Higher field strengths than clinical (7T vs 1.5T)
– Force on objects scales with field strength
• Larger magnet bores than NMR spectroscopy
– The magnet “reach” scales with bore size
• Equipment and Tools used in MRI suite
– Providing a handy supply of magnetic projectiles
Center for
In Vivo
Microscopy
NCRR
Why Bother With Magnet Safety?
• A magnet projectile presents a very real
possibility of serious injury or death
• Impact of the magnet by a projectile could
result in 3 months of system down time
• Repair costs leave less money for
science
– ($450,000 to replace a 7T magnet)
• Serious incidents lead to more onerous
safety rules and less science
Center for
In Vivo
Microscopy
NCRR
How Fast Will Objects Fly?
Notable Observations:
• Vobj
=45mph at 2T
– Equivalent to 7-story free-fall
• Vobj
=83mph at 7T
– Equivalent to 23-story free-fall
• Terminal velocity facts:
– Scales as square root of B0
– independent of mass*
• Impact energy
Center for
In Vivo
Microscopy
(See appendix for math if interested)
– Scales with mass
– Scales linearly with B0
NCRR
Forces on Objects!
B0=7T, radius=20cm
• Objects can be pulled with 50-300x
their normal gravitational weight
• Within 1 meter of scanners tools can
slip off surfaces and start accelerating
• Peak force occurs roughly 10-20cm
from magnet entrance
CIVM Incidents and Hazards
•
Peristaltic Pump stuck to 2 Tesla magnet,
•
Chair stuck to 7T magnet.
•
Surgical tools ripped from ventilator cart, stuck to 7T magnet
•
Compressed Nitrogen Tank stuck to 2 Tesla Magnet
•
Fan stuck to 2 Tesla Magnet
•
Hand-tools stuck to 7 Tesla Magnet
•
Other Hazards: motors, power supplies (in all electronics), drill
bits, cylinder caps, razor blades, screws
Center for
In Vivo
Microscopy
NCRR
Personal Safety and Nuissances
• Persons with pace makers and infusion pumps should
consult their physician before working in this
laboratory
• Remove watches, wallets, and cell phones before
entering laboratory.
• Most jewelry (gold, silver, diamond) is safe in the
magnet environment
Center for
In Vivo
Microscopy
NCRR
Our Magnet Policies
1. NO EQUIPMENT brought into lab without sign-off
and Labeling by magnet safety representative
2. NOBODY WORKS IN THIS MRI LAB until they have
completed this magnet safety training
1. And Documented it by signing their name on the wiki
3. VISITORS and AFTER HOURS WORK have
separate policies
Center for
In Vivo
Microscopy
NCRR
What About Visitors?
• Visitors may enter the MRI lab only when
accompanied by trained CIVM personnel
– Instruct visitors briefly about MRI hazards
•
Visitors must stay at least 10 feet away from
magnets (close to the door is good)
• Visitors may never assist or work in the lab
• Visitors may not enter the lab after hours
Weekends and After Hours
The magnet laboratories are available from
7:30 AM to 5:00 PM Monday through
Friday. Use on nights or weekends
requires written permission from the
Center Director
It is advisable never to bring any magnet
hazards into the lab after hours
No visitors are allowed in the MRI labs
after hours.
Working with Magnet Hazards
• Ensure the magnet hazard has been
labeled
• Ensure that someone else is present when
you move a magnet hazard in the lab
• When moving a magnet hazard don’t get
between it and the magnet
Center for
In Vivo
Microscopy
NCRR
Labels Used in Our Lab
Center for
In Vivo
Microscopy
Labels are on clipboard by 2T console. To print more, see Magnet Safety Page on Wiki
NCRR
If You Do Get Something Stuck
• Evacuate the lab
• Seek medical help (if appropriate)
• Contact magnet safety team member for
removal of object
• (get a camera and take a picture so we
can update this presentation)
Center for
In Vivo
Microscopy
NCRR
A recent incident (Jan 2011)
Rigging required to
remove pump from 7T
Motor/pump stuck to 7T
Situation:
Senior Scientist (MRI professor) visiting CIVM
Had worked at CIVM many times in the past
Carried motor/pump close to 7T before it was ripped from him
Assumed it was safe because advertised as “MR-compatible”
What went wrong?
• Despite a 5yr magnet safety training
program at CIVM, the visitor had not
completed the training.
• The object he brought in to the lab
had not been screened for magnetic
content and had not been labeled as
being a magnet hazard.
(Evan was not the guilty party)
What can you do?
• Don’t be shy about asking anybody you see in the magnet
lab if they have completed our magnet safety training
• Be vigilant about possible magnet hazards. If they are
needed in the lab, make sure they are labeled as hazards
Another recent incident (April 2012)
Janitor’s Buffer Stuck to 7T
•
Situation:
•
Janitor working on buffing floors
•
Received instruction to stay away from Magnet
•
Still got buffer sucked into the magnet
What went wrong?
• Janitor had gotten close to Bruker 7T, and 2T
without problems
• Assumed the 7T in rm 141 would be the same
• But the 7T in room 141 is UNSHIELDED
What can you do?
• Be ware that the reach of the 7T in rm 141 reaches 10x
further than the Bruker 7T (16ft reach vs 1-2 ft reach)
• Our current safety presentation is geared towards
scientists. We need another solution for non-scientists
• Need a Visceral Poster for Non-Scientists
Fact Review
• Ferrous objects are our biggest hazard
• Objects can reach 45mph in the 2T magnet and
83mph in the 7T magnet
• 1 meter from magnets, the magnetic force
becomes equal to gravitational force
• Objects can be pulled (accelerated) with 50300x their normal gravitational pull
• Labeling and your vigilance are our best defense
against a serious accident
Center for
In Vivo
Microscopy
Please sign/date training record on the Magnet Safety
Wiki page to verify that you have completed this
NCRR
Appendix for Physicists and
Engineers
How Fast Will Objects Fly?
Potential Energy of Object
Stuck in Magnet
Center for
In Vivo
Microscopy
Potential Energy of Object
Removed from Magnet
Difference must be kinetic energy prior to impact
NCRR
Projectile Velocity Estimates
Conserve Energy
• Notable Observations:
• Vobj =45mph at 2T
– Equivalent to 7-story free-fall
Treat object as iron chunk: • Vobj
=83mph at 7T
– Equivalent to 23-story free-fall
• Terminal velocity facts:
– Scales as square root of B0
– independent of mass*
Velocity scales as sqrt(B0) • Impact energy
– Scales with mass
– Scales linearly with B0
Center for
In Vivo
Microscopy
NCRR
Gradient Spatial Profile
Estimates
B0=7T, radius=20cm
Force in field gradient
Estimate scanner as
dipole loop
a
B
z
Gradient from dipole loop
Peak gradient strength
1. Peak gradient at roughly 10-20cm from edge of scanner
2. Peak gradient strength proportional to B0 and inverse of bore
size
Center
for
In Vivo
Microscopy
NCRR
Forces!
B0=7T, radius=20cm
Force on object
Point where magnetic force = gravitational force
1. Within 1m of scanners tools can slip off surfaces and
start accelerating into the magnet
2.
Objects
can be pulled with 50-300x their normal
Center
for
In Vivo
gravitational weight at peak gradient point
Microscopy
NCRR