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ANOTHER Injured Mountain Biker Had to Be Rescued



 
 
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  #1  
Old August 31st 08, 05:05 PM posted to alt.mountain-bike,rec.bicycles.soc,rec.backcountry,ca.environment,sci.environment
Mike Vandeman
external usenet poster
 
Posts: 4,798
Default ANOTHER Injured Mountain Biker Had to Be Rescued

http://www.ktvz.com/Global/story.asp?S=8928083

Injured Bend mountain biker rescued from trail

Posted: Aug 30, 2008 08:17 PM PDT

Rescuers assist injured mountain biker near Bend (8/30)
1:38

Search and Rescue crews used maps to determine were injured mtn. biker
was so they could help him out of woods

By Molly Hendrickson, KTVZ.COM and news sources

A Bend man who crashed his mountain bike and was injured on a trail in
the Dutchman Flat area west of Bend was rescued by Deschutes County
Sheriff's Search and Rescue volunteers riding ATVs - but first, they
spent some time trying to find the man in the remote location.


County 911 dispatchers got a cell phone call shortly before 11:30 a.m.
about the injured mountain bike rider on the Flag Line Trail, about 5
½ miles northeast of Dutchman Flag, said Cpl. Wayne Morgan.

Edward Wakefield, 38, an experienced mountain biker, was riding with a
friend when he fell and suffered non-life threatening injuries, Morgan
said. He was wearing a helmet at the time of the crash, but was unable
to make his way out on his own, the corporal said in a news release,
adding that "Wakefield said he did not know what happened to cause him
to crash."

Sheriff's SAR volunteers responded to the area with ATVs and medical
team personnel, Morgan said.

"Due to poor accessibility on the trails in the area, three different
rescue teams were sent in from different locations, each attempting to
reach Wakefield's location," Morgan said.

NewsChannel 21 was on the scene at the command post when the efforts
to locate Wakefield were under way. One crew member said he apparently
‘went over his handlebars" in the crash, but was "resting
comfortably."

Early on, they were unsure if he was A team reached Wakefield around 2
p.m., and he was treated at the scene by medics, then taken to Century
Drive by an ATV pulling an "ambu-sled," Morgan said.

A friend took Wakefield to St. Charles Medical Center-Bend for
treatment of a possible broken collarbone, officers said. A nursing
supervisor said he was treated and released.
--
I am working on creating wildlife habitat that is off-limits to
humans ("pure habitat"). Want to help? (I spent the previous 8
years fighting auto dependence and road construction.)

Please don't put a cell phone next to any part of your body that you are fond of!

http://home.pacbell.net/mjvande
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  #2  
Old September 1st 08, 03:10 AM posted to alt.mountain-bike,rec.bicycles.soc,rec.backcountry,ca.environment,sci.environment
Marz
external usenet poster
 
Posts: 610
Default ANOTHER Injured Mountain Biker Had to Be Rescued

http://www.komonews.com/news/27587449.html

DARRINGTON, Wash. -- Two hypothermic hikers who have been stranded in
the North Cascades since Wednesday evening will have to spend another
night in the elements, rescue officials said Thursday night.

A ground rescue team is trying to reach the hikers, who are stranded
at about 8,000 feet elevation near Spire Point northeast of
Darrington. At last report late Thursday night, the rescuers were said
to be within a couple hundred feet of the stranded pair.

A rescue helicopter from the Whidbey Island Naval Air Base tried to
reach the hikers several times, but weather conditions prevented a
rescue operation.

"We got to within 2 miles, but they're up on the face of a mountain so
that's what's preventing the search," the pilot said.

Matthew Edwards, 33, and his girlfriend, Robin Gibson, 27, both of
Wisconsin, called 911 around 7:30 p.m. Wednesday and said they were
trapped on an 18-inch ledge on a face of the mountain.

By Thursday afternoon, rescue coordinators in contact with the pair
via cell phone convinced the couple to move off of the ledge, but
there was still concern for their well-being.

"They're tired. They're cold. They're hypothermic," search and rescue
spokesman Joel Pratt said.

Edwards and Gibson had traveled to Washington to hike a portion of the
Pacific Crest Trail through the Cascades. Rescue officials said the
two hikers took a wrong turn. They hiked down a rocky area and got
scared and in over their heads.

The terrain is very rugged and the two lost most of their gear while
they were climbing down, leaving them with only one sleeping bag and
part of a tent.

A helicopter was dispatched from the Whidbey Island Naval Air Station
to rescue the two on Wednesday night, but they could not get to the
peak due to deteriorating weather conditions. A three-person "fast
team" of rescuers began hiking in Thursday morning, hoping to make it
to the two stranded hikers to provide dry clothes and food.

Later on Thursday, however, the weather had cleared enough that a Navy
helicopter was able to drop in a second rescue team. The helicopter
headed back to the scene for another possible rescue attempt Thursday,
but returned without success.

Officials hope the gear provided by the fast team will help stabilize
the two hikers so they are able to make it through another night.
Overnight lows at the hikers' location are expected to drop into the
mid 40s early Friday.

Edwards contacted rescue crews Thursday morning on his cell phone and
said the Gibson's condition was "dire," but sheriff's officials said
in a later conversation both Gibson and Edwards reported that they
were "stable."

He also told rescuers that he has hiked the same trail twice before.
  #3  
Old September 1st 08, 03:26 AM posted to alt.mountain-bike,rec.bicycles.soc,rec.backcountry,ca.environment,sci.environment
Tom Sherman[_2_]
external usenet poster
 
Posts: 9,890
Default HIKERS need to Be Rescued

Marz wrote:
http://www.komonews.com/news/27587449.html

DARRINGTON, Wash. -- Two hypothermic hikers who have been stranded in
the North Cascades since Wednesday evening will have to spend another
night in the elements, rescue officials said Thursday night.

A ground rescue team is trying to reach the hikers, who are stranded
at about 8,000 feet elevation near Spire Point northeast of
Darrington. At last report late Thursday night, the rescuers were said
to be within a couple hundred feet of the stranded pair.

A rescue helicopter from the Whidbey Island Naval Air Base tried to
reach the hikers several times, but weather conditions prevented a
rescue operation.

"We got to within 2 miles, but they're up on the face of a mountain so
that's what's preventing the search," the pilot said.

Matthew Edwards, 33, and his girlfriend, Robin Gibson, 27, both of
Wisconsin, called 911 around 7:30 p.m. Wednesday and said they were
trapped on an 18-inch ledge on a face of the mountain.

By Thursday afternoon, rescue coordinators in contact with the pair
via cell phone convinced the couple to move off of the ledge, but
there was still concern for their well-being.

"They're tired. They're cold. They're hypothermic," search and rescue
spokesman Joel Pratt said.

Edwards and Gibson had traveled to Washington to hike a portion of the
Pacific Crest Trail through the Cascades. Rescue officials said the
two hikers took a wrong turn. They hiked down a rocky area and got
scared and in over their heads.

The terrain is very rugged and the two lost most of their gear while
they were climbing down, leaving them with only one sleeping bag and
part of a tent.

A helicopter was dispatched from the Whidbey Island Naval Air Station
to rescue the two on Wednesday night, but they could not get to the
peak due to deteriorating weather conditions. A three-person "fast
team" of rescuers began hiking in Thursday morning, hoping to make it
to the two stranded hikers to provide dry clothes and food.

Later on Thursday, however, the weather had cleared enough that a Navy
helicopter was able to drop in a second rescue team. The helicopter
headed back to the scene for another possible rescue attempt Thursday,
but returned without success.

Officials hope the gear provided by the fast team will help stabilize
the two hikers so they are able to make it through another night.
Overnight lows at the hikers' location are expected to drop into the
mid 40s early Friday.

Edwards contacted rescue crews Thursday morning on his cell phone and
said the Gibson's condition was "dire," but sheriff's officials said
in a later conversation both Gibson and Edwards reported that they
were "stable."

He also told rescuers that he has hiked the same trail twice before.


Would not the rescue team of "fast hikers" get there more quickly on
mountain bikes?

--
Tom Sherman - Holstein-Friesland Bovinia
“Mary had a little lamb / And when she saw it sicken /
She shipped it off to Packingtown / And now it’s labeled chicken.”
  #4  
Old September 1st 08, 11:50 AM posted to alt.mountain-bike,rec.bicycles.soc,rec.backcountry,ca.environment,sci.environment
[email protected]
external usenet poster
 
Posts: 85
Default ANOTHER Injured Mountain Biker Had to Be Rescued

On Aug 31, 12:05*pm, Mike Vandeman wrote:
http://www.ktvz.com/Global/story.asp?S=8928083

Injured Bend mountain biker rescued from trail

snipped for clarity-
I am working on creating wildlife habitat that is off-limits to
humans ("pure habitat"). Want to help? (I spent the previous 8
years fighting auto dependence and road construction.)

Please don't put a cell phone next to any part of your body that you are fond of!

http://home.pacbell.net/mjvande



http://courses.cs.vt.edu/~cs3604/lib.../Therac_1.html
An Investigation of the Therac-25 Accidents
Nancy Leveson, University of Washington
Clark S. Turner, University of California, Irvine

Reprinted with permission, IEEE Computer, Vol. 26, No. 7, July 1993,
pp. 18-41.
Computers are increasingly being introduced into safety-critical
systems and, as a consequence, have been involved in accidents. Some
of the most widely cited software-related accidents in safety-critical
systems involved a computerized radiation therapy machine called the
Therac-25. Between June 1985 and January 1987, six known accidents
involved massive overdoses by the Therac-25 -- with resultant deaths
and serious injuries. They have been described as the worst series of
radiation accidents in the 35-year history of medical accelerators.[1]

With information for this article taken from publicly available
documents, we present a detailed accident investigation of the factors
involved in the overdoses and the attempts by the users,
manufacturers, and the US and Canadian governments to deal with them.
Our goal is to help others learn from this experience, not to
criticize the equipment's manufacturer or anyone else. The mistakes
that were made are not unique to this manufacturer but are,
unfortunately, fairly common in other safety-critical systems. As
Frank Houston of the US Food and Drug Administration (FDA) said, "A
significant amount of software for life-critical systems comes from
small firms, especially in the medical device industry; firms that fit
the profile of those resistant to or uninformed of the principles of
either system safety or software engineering."[2]

Furthermore, these problems are not limited to the medical industry.
It is still a common belief that any good engineer can build software,
regardless of whether he or she is trained in state-of-the-art
software-engineering procedures. Many companies building safety-
critical software are not using proper procedures from a software-
engineering and safety-engineering perspective.

Most accidents are system accidents; that is, they stem from complex
interactions between various components and activities. To attribute a
single cause to an accident is usually a serious mistake. In this
article, we hope to demonstrate the complex nature of accidents and
the need to investigate all aspects of system development and
operation to understand what has happened and to prevent future
accidents.

Despite what can be learned from such investigations, fears of
potential liability or loss of business make it difficult to find out
the details behind serious engineering mistakes. When the equipment is
regulated by government agencies, some information may be available.
Occasionally, major accidents draw the attention of the US Congress or
President and result in formal accident investigations (for instance,
the Rogers commission investigation of the Challenger accident and the
Kemeny commission investigation of the Three Mile Island incident).

The Therac-25 accidents are the most serious computer-related
accidents to date (at least nonmilitary and admitted) and have even
drawn the attention of the popular press. (Stories about the Therac-25
have appeared in trade journals, newspapers, People Magazine, and on
television's 20/20 and McNeil/ Lehrer News Hour.) Unfortunately, the
previous accounts of the Therac-25 problems have been oversimplified,
with misleading omissions.

In an effort to remedy this, we have obtained information from a wide
variety of sources, including lawsuits and the US and Canadian
government agencies responsible for regulating such equipment. We have
tried to be very careful to present only what we could document from
original sources, but there is no guarantee that the documentation
itself is correct. When possible, we looked for multiple confirming
sources for the more important facts.

We have tried not to bias our description of the accidents, but it is
difficult not to filter unintentionally what is described. Also, we
were unable to investigate firsthand or get information about some
aspects of the accidents that may be very relevant. For example,
detailed information about the manufacturer's software development,
management, and quality control was unavailable. We had to infer most
information about these from statements in correspondence or other
sources.

As a result, our analysis of the accidents may omit some factors. But
the facts available support previous hypotheses about the proper
development and use of software to control dangerous processes and
suggest hypotheses that need further evaluation. Following our account
of the accidents and the responses of the manufacturer, government
agencies, and users, we present what we believe are the most
compelling lessons to be learned in the context of software
engineering, safety engineering, and government and user standards and
oversight.

Genesis of the Therac-25

Medical linear accelerators (linacs) accelerate electrons to create
high- energy beams that can destroy tumors with minimal impact on the
surrounding healthy tissue. Relatively shallow tising healthy tissue.
Relatively shallow tissue is treated with the accelerated electrons;
to reach deeper tissue, the electron beam is converted into X-ray
photons.

Atomic Energy Commission Limited (AECL) and a French company called
CGR collaborated to build linear accelerators. (AECL is an arms-length
entity, called a crown corporation, of the Canadian government. Since
the time of the incidents related in this article, AECL Medical, a
division of AECL, is in the process of being privatized and is now
called Theratronics International Limited. Currently, AECL's primary
business is the design and installation of nuclear reactors.) The
products of AECL and CGR's cooperation were (1) the Therac-6, a 6
million electron volt (MeV) accelerator capable of producing X rays
only and, later, (2) the Therac-20, a 20-MeV dual-mode (X rays or
electrons) accelerator. Both were versions of older CGR machines, the
Neptune and Sagittaire, respectively, which were augmented with
computer control using a DEC PDP 11 minicomputer.

Software functionality was limited in both machines: The computer
merely added convenience to the existing hardware, which was capable
of standing alone. Industry-standard hardware safety features and
interlocks in the underlying machines were retained. We know that some
old Therac-6 software routines were used in the Therac-20 and that CGR
developed the initial software.

The business relationship between AECL and CGR faltered after the
Therac-20 effort. Citing competitive pressures, the two companies did
not renew their cooperative agreement when scheduled in 1981. In the
mid-1970s, AECL developed a radical new "double-pass" concept for
electron acceleration. A double-pass accelerator needs much less space
to develop comparable energy levels because it folds the long physical
mechanism required to accelerate the electrons, and it is more
economic to produce (since it uses a magnetron rather than a klystron
as the energy source).

Using this double-pass concept, AECL designed the Therac-25, a dual-
mode linear accelerator that can deliver either photons at 25 MeV or
electrons at various energy levels (see Figure 1. Typical Therac-25
Facility.). Compared with the Therac-20, the Therac-25 is notably more
compact, more versatile, and arguably easier to use. The higher energy
takes advantage of the phenomenon of "depth dose": As the energy
increases, the depth in the body at which maximum dose buildup occurs
also increases, sparing the tissue above the target area. Economic
advantages also come into play for the customer, since only one
machine is required for both treatment modalities (electrons and
photons).

Several features of the Therac-25 are important in understanding the
accidents. First, like the Therac-6 and the Therac-20, the Therac-25
is controlled by a PDP 11. However, AECL designed the Therac-25 to
take advantage of computer control from the outset; AECL did not build
on a stand-alone machine. The Therac-6 and Therac-20 had been designed
around machines that already had histories of clinical use without
computer control.

In addition, the Therac-25 software has more responsibility for
maintaining safety than the software in the previous machines. The
Therac-20 has independent protective circuits for monitoring electron-
beam scanning, plus mechanical interlocks for policing the machine and
ensuring safe operation. The Therac-25 relies more on software for
these functions. AECL took advantage of the computer's abilities to
control and monitor the hardware and decided not to duplicate all the
existing hardware safety mechanisms and interlocks. This approach is
becoming more common as companies decide that hardware interlocks and
backups are not worth the expense, or they put more faith (perhaps
misplaced) on software than on hardware reliability.

Finally, some software for the machines was interrelated or reused. In
a letter to a Therac-25 user, the AECL quality assurance manager said,
"The same Therac-6 package was used by the AECL software people when
they started the Therac-25 software. The Therac-20 and Therac-25
software programs were done independently, starting from a common
base." Reuse of Therac-6 design features or modules may explain some
of the problematic aspects of the Therac-25 software (see the sidebar
"Therac-25 software development and design"). The quality assurance
manager was apparently unaware that some Therac-20 routines were also
used in the Therac-25; this was discovered after a bug related to one
of the Therac-25 accidents was found in the Therac-20 software.

AECL produced the first hardwired prototype of the Therac-25 in 1976,
and the completely computerized commercial version was available in
late 1982. (The sidebars provide details about the machine's design
and controlling software, important in understanding the accidents.
Side-Bar: Therac-25 Software Development and Design)

In March 1983, AECL performed a safety analysis on the Therac-25. This
analysis was in the form of a fault tree and apparently excluded the
software. According to the final report, the analysis made several
assumptions:

(1) Programming errors have been reduced by extensive testing on a
hardware simulator and under field conditions on teletherapy units.
Any residual software errors are not included in the analysis.

(2) Program software does not degrade due to wear, fatigue, or
reproduction process.

(3) Computer execution errors are caused by faulty hardware components
and by "soft" (random) errors induced by alpha particles and
electromagnetic noise.

The fault tree resulting from this analysis does appear to include
computer failure, although apparently, judging from these assumptions,
it considers only hardware failures. For example, in one OR gate
leading to the event of getting the wrong energy, a box contains
"Computer selects wrong energy" and a probability of 10^11 is assigned
to this event. For "Computer selects wrong mode," a probability of 4 x
10^9 is given. The report provides no justification of either number.

Side-Bar: Major Event Time Line

Accident history

Eleven Therac-25s were installed: five in the US and six in Canada.
Six accidents involving massive overdoses to patients occurred between
1985 and 1987. The machine was recalled in 1987 for extensive design
changes, including hardware safeguards against software errors.

Related problems were found in the Therac-20 software. These were not
recognized until after the Therac-25 accidents because the Therac-20
included hardware safety interlocks and thus no injuries resulted.

In this section, we present a chro-nological account of the accidents
and the responses from the manufacturer, government regulatory
agencies, and users.users.

Kennestone Regional Oncology Center, 1985. Details of this accident in
Marietta, Georgia, are sketchy since it was never carefully
investigated. There was no admission that the injury was caused by the
Therac-25 until long after the occurrence, despite claims by the
patient that she had been injured during treatment, the obvious and
severe radiation burns the patient suffered, and the suspicions of the
radiation physicist involved.

After undergoing a lumpectomy to remove a malignant breast tumor, a 61-
year-old woman was receiving follow-up radiation treatment to nearby
lymph nodes on a Therac-25 at the Kennestone facility in Marietta. The
Therac-25 had been operating at Kennestone for about six months; other
Therac-25s had been operating, apparently without incident, since
1983.

On June 3, 1985, the patient was set up for a 10-MeV electron
treatment to the clavicle area. When the machine turned on, she felt a
"tremendous force of heat . . . this red-hot sensation." When the
technician came in, the patient said, "You burned me." The technician
replied that that was not possible. Although there were no marks on
the patient at the time, the treatment area felt "warm to the touch."

It is unclear exactly when AECL learned about this incident. Tim
Still, the Kennestone physicist, said that he contacted AECL to ask if
the Therac-25 could operate in electron mode without scanning to
spread the beam. Three days later, the engineers at AECL called the
physicist back to explain that improper scanning was not possible.

In an August 19, 1986, letter from AECL to the FDA, the AECL quality
assurance manager said, "In March of 1986, AECL received a lawsuit
from the patient involved. . . This incident was never reported to
AECL prior to this date, although some rather odd questions had been
posed by Tim Still, the hospital physicist." The physicist at a
hospital in Tyler, Texas, where a later accident occurred, reported,
"According to Tim Still, the patient filed suit in October 1985
listing the hospital, manufacturer, and service organization
responsible for the machine. AECL was notified informally about the
suit by the hospital, and AECL received official notification of a
lawsuit in November 1985."

Because of the lawsuit (filed on November 13, 1985), some AECL
administrators must have known about the Marietta accident -- although
no investigation occurred at this time. Further comments by FDA
investigators point to the lack of a mechanism in AECL to follow up
reports of suspected accidents. The lack of follow-up in this case
appears to be evidence of such a problem in the organization.

The patient went home, but shortly afterward she developed a reddening
and swelling in the center of the treatment area. Her pain had
increased to the point that her shoulder "froze" and she experienced
spasms. She was admitted to West Paces Ferry Hospital in Atlanta, but
her oncologists continued to send her to Kennestone for Therac-25
treatments. Clinical explanation was sought for the reddening of the
skin, which at first her oncologist attributed to her disease or to
normal treatment reaction.

About two weeks later, the physicist at Kennestone noticed that the
patient had a matching reddening on her back as though a burn had gone
through her body, and the swollen area had begun to slough off layers
of skin. Her shoulder was immobile, and she was apparently in great
pain. It was obvious that she had a radiation burn, but the hospital
and her doctors could provide no satisfactory explanation. Shortly
afterward, she initiated a lawsuit against the hospital and AECL
regarding her injury.

The Kennestone physicist later estimated that she received one or two
doses of radiation in the 15,000- to 20,000-rad (radiation absorbed
dose) range. He does not believe her injury could have been caused by
less than 8,000 rads. Typical single therapeutic doses are in the 200-
rad range. Doses of 1,000 rads can be fatal if delivered to the whole
body; in fact, the accepted figure for whole-body radiation that will
cause death in 50 percent of the cases is 500 rads. The consequences
of an overdose to a smaller part of the body depend on the tissue's
radiosensitivity. The director of radiation oncology at the Kennestone
facility explained their confusion about the accident as due to the
fact that they had never seen an overtreatment of that magnitude
before.

Eventually, the patient's breast had to be removed because of the
radiation burns. She completely lost the use of her shoulder and her
arm, and was in constant pain. She had suffered a serious radiation
burn, but the manufacturer and operators of the machine refused to
believe that it could have been caused by the Therac-25. The treatment
prescription printout feature was disabled at the time of the
accident, so there was no hard copy of the treatment data. The lawsuit
was eventually settled out of court.

From what we can determine, the accident was not reported to the FDA
until after the later Tyler accidents in 1986 (described in later
sections). The reporting regulations for medical device incidents at
that time applied only to equipment manufacturers and importers, not
users. The regulations required that manufacturers and importers
report deaths, serious injuries, or malfunctions that could result in
those consequences. Health-care professionals and institutions were
not required to report incidents to manufacturers. (The law was
amended in 1990 to require health-care facilities to report incidents
to the manufacturer and the FDA.) The comptroller general of the US
Government Accounting Office, in testimony before Congress on November
6, 1989, expressed great concern about the viability of the incident-
reporting regulations in preventing or spotting medical-device
problems. According to a GAO study, the FDA knows of less than 1
percent of deaths, serious injuries, or equipment malfunctions that
occur in hospitals.[3]

At this point, the other Therac-25 users were unaware that anything
untoward had occurred and did not learn about any problems with the
machine until after subsequent accidents. Even then, most of their
information came through personal communication among themselves.

Ontario Cancer Foundation, 1985. The second in this series of
accidents occurred at this Hamilton, Ontario, Canada, clinic about
seven weeks after the Kennestone patient was overdosed. At that time,
the Therac-25 at the Hamilton clinic had been in use for more than six
months. On July 26, 1985, a 40-year-old patient came to the clinic for
her 24th Therac-25 treatment for carcinoma of the cervix. The operator
activated the machine, but the Therac shut down after five seconds
with an "H-tilt" error message. The Therac's dosimetry system display
read "no dose" and indicated a "treatment pause."

Since the machine did not suspend and the control display indicated no
dose was delivered to the patient, the operator went ahead with a
second attempt at treatment by pressing the "P" key (the proceed
command), expecting the machine to deliver the proper dose this time.
This was standard operating procedure and, as described in the sidebar
The operator interface, Therac-25 operators had become accustomed to
frequent malfunctions that had no untoward consequences for the
patient. Again, the machine shut down in the same manner. The operator
repeated this process four times after the original attempt -- the
display showing "no dose" delivered to the patient each time. After
the fifth pause, the machine went into treatment suspend, and a
hospital service technician was called. The technician found nothing
wrong with the machine. This also was not an unusual scenario,
according to a Therac-25 operator.

After the treatment, the patient complained of a burning sensation,
described as an "electric tingling shock" to the treatment area in her
hip. Six other patients were treated later that day without incident.
The patient came back for further treatment on July 29 and complained
of burning, hip pain, and excessive swelling in the region of
treatment. The machine was taken out of service, as radiation
overexposure was suspected. The patient was hospitalized for the
condition on July 30. AECL was informed of the apparent radiation
injury and sent a service engineer to investigate. The FDA, the then-
Canadian Radiation Protection Bureau (CRPB), and the users were
informed that there was a problem, although the users claim that they
were never informed that a patient injury had occurred. (On April 1,
1986, the CRPB and the Bureau of Medical Devices were merged to form
the Bureau of Radiation and Medical Devices or BRMD.) Users were told
that they should visually confirm the turntable alignment until
further notice (which occurred three months later).

The patient died on November 3, 1985, of an extremely virulent cancer.
An autopsy revealed the cause of death as the cancer, but it was noted
that had she not died, a total hip replacement would have been
necessary as a result of the radiation overexposure. An AECL
technician later estimated the patient had received between 13,000 and
17,000 rads.

Manufacturer response. AECL could not reproduce the malfunction that
had occurred, but suspected a transient failure in the microswitch
used to determine turntable position. During the investigation of the
accident, AECL hardwired the error conditions they assumed were
necessary for the malfunction and, as a result, found some design
weaknesses and potential mechanical problems involving the turntable
positioning.

The computer senses and controls turntable position by reading a 3-bit
signal about the status of three microswitches in the turntable switch
assembly (see the sidebar Turntable positioning). Essentially, AECL
determined that a 1-bit error in the microswitch codes (which could be
caused by a single open-circuit fault on the switch lines) could
produce an ambiguous position message for the computer. The problem
was exacerbated by the design of the mechanism that extends a plunger
to lock the turntable when it is in one of the three cardinal
positions: The plunger could be extended when the turntable was way
out of position, thus giving a second false position indication. AECL
devised a method to indicate turntable position that tolerated a 1-bit
error: The code would still unambiguously reveal correct position with
any one microswitch failure.

In addition, AECL altered the software so that the computer checked
for "in transit" status of the switches to keep further track of the
switch operation and the turntable position, and to give additional
assurance that the switches were working and the turntable was moving.

As a result of these improvements, AECL claimed in its report and
correspondence with hospitals that "analysis of the hazard rate of the
new solution indicates an improvement over the old system by at least
five orders of magnitude." A claim that safety had been improved by
five orders of magnitude seems exaggerated, especially given that in
its final incident report to the FDA, AECL concluded that it "cannot
be firm on the exact cause of the accident but can only suspect. . ."
This underscores the company's inability to determine the cause of the
accident with any certainty. The AECL quality assurance manager
testified that AECL could not reproduce the switch malfunction and
that testing of the microswitch was "inconclusive." The similarity of
the errant behavior and the injuries to patients in this accident and
a later one in Yakima, Washington, (attributed to software error)
provide good reason to believe that the Hamilton overdose was probably
related to software error rather than to a microswitch failure.

Government and user response. The Hamilton accident resulted in a
voluntary recall by AECL, and the FDA termed it a Class II recall.
Class II means "a situation in which the use of, or exposure to, a
violative product may cause temporary or medically reversible adverse
health consequences or where the probability of serious adverse health
consequences is remote." Four users in the US were advised by a letter
from AECL on August 1, 1985, to visually check the ionization chamber
to make sure it was in its correct position in the collimator opening
before any treatment and to discontinue treatment if they got an H-
tilt message with an incorrect dose indicated. The letter did not
mention that a patient injury was involved. The FDA audited AECL's
subsequent modifications. After the modifications, the users were told
that they could return to normal operating procedures.

As a result of the Hamilton accident, the head of advanced X-ray
systems in the CRPB, Gordon Symonds, wrote a report that analyzed the
design and performance characteristics of the Therac-25 with respect
to radiation safety. Besides citing the flawed microswitch, the report
faulted both hardware and software components of the Therac's design.
It concluded with a list of four modifications to the Therac-25
necessary for minimum compliance with Canada's Radiation Emitting
Devices (RED) Act. The RED law, enacted in 1971, gives government
officials power to ensure the safety of radiation-emitting devices.

The modifications recommended in the Symonds report included
redesigning the microswitch and changing the way the computer handled
malfunction conditions. In particular, treatment was to be terminated
in the event of a dose-rate malfunction, giving a treatment "suspend."
This would have removed the option to proceed simply by pressing the
"P" key. The report also made recommendations regarding collimator
test procedures and message and command formats. A November 8, 1985
letter signed by Ernest Létourneau, M.D., director of the CRPB, asked
that AECL make changes to the Therac-25 based on the Symonds report
"to be in compliance with the RED Act."

Although, as noted above, AECL did make the microswitch changes, it
did not comply with the directive to change the malfunction pause
behavior into treatment suspends, instead reducing the maximum number
of retries from five to three. According to Symonds, the deficiencies
outlined in the CRPB letter of November 8 were still pending when
subsequent accidents five months later changed the priorities. If
these later accidents had not occurred, AECL would have been compelled
to comply with the requirements in the letter.

Immediately after the Hamilton accident, the Ontario Cancer Foundation
hired an independent consultant to investigate. He concluded in a
September 1985 report that an independent system (beside the computer)
was needed to verify turntable position and suggested the use of a
potentiometer. The CRPB wrote a letter to AECL in November 1985
requesting that AECL install such an independent upper collimator
positioning interlock on the Therac-25. Also, in January 1986, AECL
received a letter from the attorney representing the Hamilton clinic.
The letter said there had been continuing problems with the turntable,
including four incidents at Hamilton, and requested the installation
of an independent system (potentiometer) to verify turntable position.
AECL did not comply: No independent interlock was installed on the
Therac-25s at this time.



Mike should be working the next 8 years on a computer free zone. Mike
is living proof that radiation causes brain injuries.

  #5  
Old September 2nd 08, 01:40 PM posted to alt.mountain-bike,rec.bicycles.soc,rec.backcountry,ca.environment,sci.environment
Stormin Mormon[_2_]
external usenet poster
 
Posts: 17
Default HIKERS need to Be Rescued

Cold and hypothermic both? Why can't people be warm and snuggly when they
are hyopthermic. Much more comfortable.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"Tom Sherman" wrote in message
...
Marz wrote:
http://www.komonews.com/news/27587449.html


"They're tired. They're cold. They're hypothermic," search and rescue
spokesman Joel Pratt said.



  #6  
Old September 3rd 08, 12:20 AM posted to alt.mountain-bike,rec.bicycles.soc,rec.backcountry,ca.environment,sci.environment
Tom Sherman[_2_]
external usenet poster
 
Posts: 9,890
Default HIKERS need to Be Rescued

Stormin Mormon wrote:
Cold and hypothermic both? Why can't people be warm and snuggly when they
are hyopthermic.[...]

TOP POSTING.

--
Tom Sherman - Holstein-Friesland Bovinia
“Mary had a little lamb / And when she saw it sicken /
She shipped it off to Packingtown / And now it’s labeled chicken.”
  #7  
Old September 5th 08, 02:15 AM posted to alt.mountain-bike,rec.bicycles.soc,rec.backcountry,ca.environment,sci.environment
Stormin Mormon[_2_]
external usenet poster
 
Posts: 17
Default HIKERS need to Be Rescued

Does top posting cause hypothermia?

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"Tom Sherman" wrote in message
...
Stormin Mormon wrote:
Cold and hypothermic both? Why can't people be warm and snuggly when they
are hyopthermic.[...]

TOP POSTING.

--
Tom Sherman - Holstein-Friesland Bovinia
“Mary had a little lamb / And when she saw it sicken /
She shipped it off to Packingtown / And now it’s labeled chicken.”


  #8  
Old September 5th 08, 02:32 AM posted to alt.mountain-bike,rec.bicycles.soc,rec.backcountry,ca.environment,sci.environment
Tom Sherman[_2_]
external usenet poster
 
Posts: 9,890
Default HIKERS need to Be Rescued

Stormin Mormon aka Christopher A. Young wrote:
Does top posting cause hypothermia?

YES.

A. Top posting.
Q. What is the most annoying thing on Usenet?

--
Tom Sherman - Holstein-Friesland Bovinia
“Mary had a little lamb / And when she saw it sicken /
She shipped it off to Packingtown / And now it’s labeled chicken.”
 




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