AW: [ RadSafe ] 1. official Belgian report on the Sterigenicsradiationaccident

Thu Apr 13 13:52:11 CDT 2006

Grant:

The quoted range of uncertainty of the dose, +/-4.3%, definitely appears to be rather small!

Stated without further qualification one might assume that it represents some 'standard error'. Assuming the estimate stems from counting chromosome aberrations in peripheral lymphocytes (which in fact have been analysed), and assuming that the Poisson distribution pertains to these counts (which for low-LET radiation is reasonable), a total count of 529 aberrations would be required to achieve this standard error. Taking the central value D=4.6 Gy for the dose and assuming that dicentric chromosomes as the most frequently studied aberration have been assessed, then the data from 

Edwards A A, Virsik-Peuckert P, Bryant P, Mechanisms of radiation-induced chromosome aberrations. Mutation Research 366(1996)117-128.

would yield a frequency of 
A = 0.037 * D + 0.067 * D^2 = 1.588 
dicentric chromosomes per cell. 

This implies that you would have to analyse the karyotypes of 529/1.588 = 333 lymphocytes in order to reach that precision. Actually in such instances you more often analyse 1000 and more cells so that from a purely statistical point of view the above uncertainty does not look too extraordinary after all. Of course my argument does not account for any systematic uncertainties including the uncertainties of the above parameter values and age corrections. On the other hand it has been reported that additional measurements with a phantom were performed in the irradiation room GAMIRR II which might further add to reduce the uncertainties of the dose assessment.

Best regards, Rainer

________________________________

Von: NIXON, Grant [mailto:Grant.NIXON at mdsinc.com]
Gesendet: Do 13.04.2006 15:57
An: Facius, Rainer
Betreff: RE: [ RadSafe ] 1. official Belgian report on the Sterigenicsradiationaccident

Hi Rainer:

Indeed.

I also wonder what method was used to so tightly bracket the level of exposure (e.g., did they draw a tooth?)

Notwithstanding deep concerns for the unfortunate victim, this wholly preventable incident deals a serious blow to the entire industry, drawing unwanted attention from various groups to an industry that is arguably one of the safest in the world by any objective measure.

Grant

Grant I. Nixon, Ph. D., P. Phys.
Radiation Physicist
Engineering
MDS Nordion
Tel: (613) 592 3400 ext. 2869
Fax:( 613) 592 7423

-----Original Message-----
From: Rainer.Facius at dlr.de [mailto:Rainer.Facius at dlr.de]
Sent: Thursday, April 13, 2006 5:19 AM
To: NIXON, Grant; radsafe at radlab.nl
Subject: AW: [ RadSafe ] 1. official Belgian report on the Sterigenicsradiationaccident

Grant:

Most pertinent questions indeed!

I add my already voiced mystification why the ensuing symptoms of early radiation sickness which at about 4.6 Gy must have been substantial were not associated with his preceding trouble shooting service on the false alarms - neither by him nor by his physician - for another three weeks.

Rainer

Dr. Rainer Facius
German Aerospace Center
Institute of Aerospace Medicine
Linder Hoehe
51147 Koeln
GERMANY
Voice: +49 2203 601 3147 or 3150
FAX:   +49 2203 61970

-----Ursprüngliche Nachricht-----
Von: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] Im Auftrag von NIXON, Grant
Gesendet: Mittwoch, 12. April 2006 22:23
An: radsafe at radlab.nl
Betreff: RE: [ RadSafe ] 1. official Belgian report on the Sterigenicsradiationaccident

Of course, there are other questions.

Why would the operator, a veteran of some 24 years, enter the room to initiate the startup procedure without a survey meter in hand? Our employees do not enter irradiation chambers without a direct reading/alarming dosimeter in addition to their survey meters, the latter are checked for audible signal and needle deflection prior to entry (with a check source stationed near the entrance).

As a matter of practice, the source is always considered to be in the "irradiate position" before entry into an irradiation chamber. This is irrespective of control systems and alarms. In this case, the alarm system had been active prior to entry.

The operator also failed to notice the source rack out of the pool.

Otherwise intelligent people are capable of committing foolish acts when their minds are not properly engaged and focused on the hazards of the job. Interlocks and safety systems are great but they are no substitute. The right attitude, a culture of safety, and a healthy respect for the potential dangers of ionizing radiation must remain at the forefront of one's mind when on a job. This respect and presence of mind must persist and not fade with experience.

Grant Nixon

-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On Behalf Of Rainer.Facius at dlr.de
Sent: Wednesday, April 12, 2006 3:07 PM
To: radsafe at radlab.nl
Subject: [ RadSafe ] 1. official Belgian report on the Sterigenics radiationaccident

The Belgian Federal Agency for Nuclear Control (AFCN) responsible for the investigations on the accident has released its first communiqué on the Sterigenics radiation accident.

http://www.fanc.fgov.be/fr/news_2006_04_11_dossier_streigenics.htm (20060412)

(1) The dose estimate has been raised to between 4.4 to 4.8 Sv

(2) No other person has unduly been exposed.

(3) Instrumental to the Co-60 source not being in its home position was a defect in the control system for the hydraulic gear moving the source, leading to an "oscillatory and inopportune" movement of the source holder. "Interferences between the hydraulic systems for the two irradiation rooms" GAMIRR I and GAMIRR II are hypothesized to have triggered these oscillations.

(4) No word why the ambient dose-rate meters inside GAMIRR II did not work or why the entrance was not interlocked as it should when the source is not in its home position.

Rainer

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