where expertise comes together - since 1996

Web's Largest Portal of Nondestructive Testing (NDT)
Open Access Database (Conference Proceedings, Articles, News), Exhibition, Forum, Network

All Forum Boards
Technical Discussions >
Safe Working Distance for Radiography
Career Discussions
Job Offers
Job Seeks
Classified Ads
About NDT.net
Articles & News

34192 views
05:22 Jun-20-2005
John D
Safe Working Distance for Radiography

Can someone help me out? I am trying to figure out how do radiographers calculate the safe working distance from a source. We are in a shutdown and have maintenance crews working in the same areas as RT crews. I know the inverse square law gives us that information, but that is theoretical. What about if they are using a collimator and the pipe is 1/2" thick with a double wall exposure. What would be the actual distance? And what about the direction of the radiation?
Thanks in advance for your help.


 
00:45 Jun-20-2005
Mathias
Re: Safe Working Distance for Radiography You must have a physical barrier at 7.5 ìSv/hr. How do you achieve this? Let’s say you use 250 kV and 4 mA in your example. If no object is in the way for the radiation this gives 6 Sv/hr at 1 metre. If you then use the inverse square law the safety distance is 895 m. For steel and 250 kV the half value layer is 12 mm. So if the incoming radiation is 6 Sv/hr the radiation out is approx. 3 Sv/hr, then you need a safety distance of… 632 m. –Wow. This is how to calculate the safety distance for the central beam of radiation, but in the real life you have other objects around you that absorb the radiation (pipes, valves, etc.), so if don’t want to set up a barrier around half the world you need to measure the radiation level with a dose rate meter.

----------- Start Original Message -----------
: Can someone help me out? I am trying to figure out how do radiographers calculate the safe working distance from a source. We are in a shutdown and have maintenance crews working in the same areas as RT crews. I know the inverse square law gives us that information, but that is theoretical. What about if they are using a collimator and the pipe is 1/2" thick with a double wall exposure. What would be the actual distance? And what about the direction of the radiation?
: Thanks in advance for your help.
------------ End Original Message ------------




 
01:37 Jun-20-2005
JohnD
Re: Safe Working Distance for Radiography ----------- Start Original Message -----------
: You must have a physical barrier at 7.5 ìSv/hr. How do you achieve this? Let’s say you use 250 kV and 4 mA in your example. If no object is in the way for the radiation this gives 6 Sv/hr at 1 metre. If you then use the inverse square law the safety distance is 895 m. For steel and 250 kV the half value layer is 12 mm. So if the incoming radiation is 6 Sv/hr the radiation out is approx. 3 Sv/hr, then you need a safety distance of… 632 m. –Wow. This is how to calculate the safety distance for the central beam of radiation, but in the real life you have other objects around you that absorb the radiation (pipes, valves, etc.), so if don’t want to set up a barrier around half the world you need to measure the radiation level with a dose rate meter.
: : Can someone help me out? I am trying to figure out how do radiographers calculate the safe working distance from a source. We are in a shutdown and have maintenance crews working in the same areas as RT crews. I know the inverse square law gives us that information, but that is theoretical. What about if they are using a collimator and the pipe is 1/2" thick with a double wall exposure. What would be the actual distance? And what about the direction of the radiation?
: : Thanks in advance for your help.
------------ End Original Message ------------

But that's what I am asking. How do you calculate the safe distance if there are things inthe way. Like the pipe you are shooting for example. I know the Inverse Square Law.



 
00:15 Jun-20-2005
Zeki Cosku Gokce
Re: Safe Working Distance for Radiography The calculations are only used for starting point. Even if you used the colimator you will still have some leakage. So you cannot guarantee the accuracy of your calculations. I know when you apply for the permit the Plant HSE people would like to see everything in writing. The way I used to get around it was I would make a detailed calculation for a specific joint (usually the worst case scenario) And also explained them on the meeting that this would be the case if there were nothing around the radiography crew and the real controlled area would be found by measuring the radiation using the calculation as a guide. Also you have to remember as long as you controlled the people in the controlled area they can work in side your controlled area. That means if someone needs to get readings or the plant control room is in the limits of your controlled area. Then you issue everyone a dosimeter and make sure they use it.




 
01:41 Jul-15-2008
Hannes
Re: Safe Working Distance for Radiography Hi there,

You can use the following formula;

A = Ao X e -((LIN2/HVL) X Thickness of steel)

If you need more info just mail me.


 
10:40 Jan-22-2012
AMINE
Re: Safe Working Distance for Radiography In Reply to Hannes at 01:41 Jul-15-2008 .

Dear Hannes ,

Could you please help me urgently , Could you give me all the details concerning the calculation of the safe distance during radiography , We are using currently in our site sources of 10, 25, 20 , 35 and 40 curies .Your urgent reply will be highly appreciated.

Best Regards

Amine

 
19:10 Jan-23-2012

Csaba Hollo

, Senior Technician
Acuren Group Inc.,
Canada,
Joined Feb 2010
301
Re: Safe Working Distance for Radiography In Reply to AMINE at 10:40 Jan-22-2012 .

For Iridium 192, your factors are 480 mR(4.8 mSv)/hr/ci @1meter
For Cobalt 60, it is 1.35 R (13.5 mSv)/hr/ci @ 1 meter
For Selenium 75 it is 200 mR (2 mSv)/hr/ci @ 1 meter

Calculate your half or tenth value layers for your shielding, then use the inverse square law for intensity. (twice the distance=one quarter the intensity, conversely, one half the distance=4 times the intensity). Depending on your regulatory boundary limits for exposure to the public, safe distances may vary.
You have to be prepared to understand how the calculations work, and to be able to work this out for yourself as part of your radiation protection plan.

 
20:12 Jan-23-2012
Brent
Re: Safe Working Distance for Radiography In Reply to Csaba Hollo at 19:10 Jan-23-2012 .

Don't forget that after all calculations are made you have to test the actual mSv/hour delivered at the barrier all the way around. Calculations are just there to help you guess at the safe distance and the barrier limit is determined by your countries regulations.

 
10:50 Dec-26-2013
Vinoth kumar Kannan
Re: Safe Working Distance for Radiography In Reply to Hannes at 01:41 Jul-15-2008 .

Dear Sir/Madam,

Kindly send me the detail abbreviations for Formula A = Ao X e -((LIN2/HVL) X Thickness of steel) please.

Regards,

Vinoth kumar Kannan

 
19:50 Jan-04-2014

Babu Ram Sharma

NDT Inspector, Welding Inspector CSWIP 3.1, Radiation Safety Officer (RSO)
RGF NDT & Inspection Division,
Saudi Arabia,
Joined Jan 2014
6
Re: Safe Working Distance for Radiography In Reply to Vinoth kumar Kannan at 10:50 Dec-26-2013 .

Mr. Vinoth kumar Kannan,

in the formula: A = Ao X e -((LIN2/HVL) X Thickness of steel

A= Final Activity in Curie
Ao= Initial activity in Curie
e= Exponantial
L1N2= constant value(0.6932)
HVL= Half value layer of Steel (ie. 12.5 mm)
and, thickness of steel which is used for shielding.

Thanks.

 
17:36 Aug-22-2014
y rajasekhar reddy
Re: Safe Working Distance for Radiography In Reply to AMINE at 10:40 Jan-22-2012 .



y.rajasekhar reddy


Could you please help me urgently , Could you give me all the details concerning the calculation of the safe distance during radiography , We are using currently in our site sources of 10, 25, 20 , 35 and 40 curies .Your urgent reply will be highly appreciated.

Best Regards

 
17:41 Aug-22-2014
rajasekhar reddy
Re: Safe Working Distance for Radiography In Reply to Zeki Cosku Gokce at 00:15 Jun-20-2005 .

y rajasekhar reddy

Radiography test is 1 curies ho much safe area is covered the barrigation.please give the answer.

 
18:44 Feb-12-2015
salim
Re: Safe Working Distance for Radiography In Reply to Hannes at 01:41 Jul-15-2008 .

please tell what is the safe distence from origin

 
05:56 Apr-10-2015
Akbar shaik
Re: Safe Working Distance for Radiography In Reply to Hannes at 01:41 Jul-15-2008 .

Mr.Hannes,
would you please provide the complete details for calculating the safe barrier distance with various strengths of ir-192. expecting a formula from you sir.

thanking you sir.
Regards, Akbar shaik

 
22:56 Apr-10-2015

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
804
Re: Safe Working Distance for Radiography In Reply to Akbar shaik at 05:56 Apr-10-2015 .

Akbar,

Csaba gave you all the information to calculate your safe distance. What more do you want? Do we have to go do your job and put your barriers up, crank your source and process and read your film?

 
02:49 Apr-12-2015
guest
Re: Safe Working Distance for Radiography In Reply to Michel Couture at 22:56 Apr-10-2015 .

There is a shielding and distance calculator for gamma on the ATTAR website in the download section.

www.attar.com.au



 
11:43 Apr-13-2015
Sami
Re: Safe Working Distance for Radiography In Reply to y rajasekhar reddy at 17:36 Aug-22-2014 .

For Ir 192 gamma source the dose rate at 1 meter is 13mGy/hr/Ci
to calculate the safe distance for safety barriers 7.5microSv/hr
conversion factor from mGy to microGy
1 is the Q factor for Gamma Ray
D1=1

D2 = root of (D1 square X 13mGy/hr/Ci X 1000 X 1X Ci used)/( 7.5 microSv/hr))

 
07:15 Apr-17-2015

Denver

Engineering,
United Arab Emirates (UAE),
Joined Apr 2015
5
Re: Safe Working Distance for Radiography In Reply to Sami at 11:43 Apr-13-2015 .

The guidance document ANSI Z54.1-1963 will tell you to set (adjust) the distance (boundary) away from an x-ray source so that a member of the public (nonbadged person) will not get more that 2 millirem (mrem) in an hour, and not more than 100 mrem in a year. A mrem is a dose of radiation; and in SI units would be 0.02 milllisieverts (mSv) in an hour, and not more than 1 mSv in a year. Each person in the United States gets an average of 7 to 8 mSv every year from medical and natural radiation exposure. The safe separation (boundary) distance depends on (1) the intensity of the x ray or gamma radiation source, (2) how long the source must be used to get a proper image (how long the x-ray machine must be turned on, or how long a gamma radiation source must out of its camera [portable-shield]), and (3) any added shielding used to reduce the radiation dose rate around the source of x rays or gamma radiation. Regulations require that a qualified radiographer must use a radiation survey meter to measure the radiation dose rate around the item being x rayed and then sets up a boundary to keep people (members of the public) away from the area so the limits (given above) are not exceeded. You can purchase the document, ANSI Z54.1-1963, from the American National Standards Institute (ANSI) at its website or from the IHS Standards Store.

 
11:35 Apr-17-2015

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
804
Re: Safe Working Distance for Radiography In Reply to Denver at 07:15 Apr-17-2015 .

Denver,

I guess it would be safer to set your barriers iaw the local laws. In some countries the members of the general public have lower limits than the one you have stated. In Canada for example, it is 1mR.

 
12:07 May-02-2015

Shankar Arumugam

Other, NDE Engineer
India,
Joined Oct 2013
38
Re: Safe Working Distance for Radiography In Reply to Michel Couture at 11:35 Apr-17-2015 .

Safe working distance for Radiography calculation (panaromic radiation -360 deg)

Safe distance =Sqr. root [(Ci x RHM x W x T) / P]

where
Ci - Curie strength
RHM - Roentgen/Hour/Meter (for Ir192-0.48, Co60-1.3)
W - Work Load (No. of exposures per week x duration of exposure in minutes)
T - Occupancy factor (full ocupancy -1 ; partial ocupancy - 1/4 ; rare ocupancy - 1/16)
P- Permissible does (permissible dose for public in your country/week)

this formula will help to calculate safe working distance from radiation zone.

 
12:05 Jul-14-2015
ndt technician
Re: Safe Working Distance for Radiography In Reply to Zeki Cosku Gokce at 00:15 Jun-20-2005 .

sir can you teach me how to use or calculate safedistance with collimator using inverse square law?? tnx sir for helping

 
09:01 Jul-22-2015
Menon
Re: Safe Working Distance for Radiography In Reply to Zeki Cosku Gokce at 00:15 Jun-20-2005 .

What should be the safe distance maintained for a Radiography work by using

SOURCE TYPE STRENGTH TIME OF EXPOSURE
Ir-192 80 CURIE 25 HOURS

 
18:15 Jul-22-2015

Csaba Hollo

, Senior Technician
Acuren Group Inc.,
Canada,
Joined Feb 2010
301
Re: Safe Working Distance for Radiography In Reply to Menon at 09:01 Jul-22-2015 .

Honestly, guys.

The formulas have been given. If you can't do the calculations, you really shouldn't be in NDT.

 
06:52 Sep-12-2015
Franie Louie Ferolino
Re: Safe Working Distance for Radiography In Reply to Hannes at 01:41 Jul-15-2008 .

hi there,

if any one can help me... i was calculating for the safe distance after the shielding or the material being radiograp but was not able to come up with the right answer. please help me....

i have a panoramic exposure for cylindrical tank with 36mm thickness, 8 meter inside diameter. Ir-192 : 90Ci activity. i would like to know how much activity after the 36mm material thickness (or Outside of tank).

thank you....

 
17:18 Sep-17-2015

Sys

Other, Shared Resources Manager (HT, Chemical Processing, NDT & CMM)
UTC AEROSPACE SYSTEMS,
Indonesia,
Joined Sep 2015
7
Re: Safe Working Distance for Radiography In Reply to Franie Louie Ferolino at 06:52 Sep-12-2015 .

Dear All,
3 basic principle "Safety" in Radiography activity, are:
- Distance--> Far away is better
- Time, and--> Faster is better
- Shielding-->Thicker is better

@Franie Louie Ferolino
The Formula been delivered by Hannes

@Csaba Hello
I agreed with you

 
13:17 Dec-18-2015
mofadel
Re: Safe Working Distance for Radiography In Reply to Hannes at 01:41 Jul-15-2008 .

hello dear
kindly if you have any text regarding the exposure distance and the techniques used in radiographics such DWDI.SWSI,DWSI etc..
i need to know the procedure for set the radiation source which either x-ray or camera and its proper distance from pipes.
thanks in advanced

 
04:51 Nov-09-2016
ADNAN
Re: Safe Working Distance for Radiography In Reply to John D at 05:22 Jun-20-2005 (Opening).

If radiography is going on about 8 meters per side then what is the total length of barricaded area required

 
07:39 Nov-09-2016
Guest
Re: Safe Working Distance for Radiography In Reply to ADNAN at 04:51 Nov-09-2016 .

try this for approximate values

http://www.attar.com.au/uploadimage/Product/ProductImg/radiation_exposure.xls

 
06:30 Nov-30-2016
Sumaiya
Re: Safe Working Distance for Radiography In Reply to Hannes at 01:41 Jul-15-2008 .

Hey,
Greetings!!!
M primi with 16wks of pregnancy.My working placement is about 5-6 ft away from X-ray room.Is it harmful for fetus??M little bit tense.Please let me know..

Regards
Sumaiya

 
09:16 Nov-30-2016

S V Swamy

Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex ,
India,
Joined Feb 2001
782
Re: Safe Working Distance for Radiography In Reply to Sumaiya at 06:30 Nov-30-2016 .

It may safe if enough shielding is provided in the X-ray room. It is always good to get the dosage checked with a dosimeter. Another factor would be the amount of time that you spend in that area. If possible, spend less time there and more time at another place far from any radiation source.

If you are working with radiation, you should be provided with a personal badge that would be periodically monitored.

Best wishes to you and the baby inside.

Swamy
Hyderabad, India

 
15:08 Apr-04-2017
Anto jeyson
Re: Safe Working Distance for Radiography In Reply to Babu Ram Sharma at 19:50 Jan-04-2014 .

Can you explain the garden of distance for X-ray machine,
160kv 0.5 mA

 
16:34 Apr-10-2017

Zscherpel, Uwe

R & D,
BAM Berlin,
Germany,
Joined Jan 2010
67
Re: Safe Working Distance for Radiography In Reply to Anto jeyson at 15:08 Apr-04-2017 .

Dear John D.,
just a hint: real radiographers do not calculate, because there are too many incalculable influences. So they just went to the site and move the source to the active position. Than they measure the dose rate and a typical value for the controlled area is set by 40 micro Gray/h at least in Europe.
Best regards
Uwe Z.

 
16:44 Apr-12-2017

Anto jeyson

India,
Joined Apr 2017
1
Re: Safe Working Distance for Radiography In Reply to Zscherpel, Uwe at 16:34 Apr-10-2017 .

Anyone please explain me that
We didn't get sharpe image in computerised radiography (phorspher plate) while using X-ray tube.
Image is very sharpe while using iridium 192.
So what is the issues?
Why couldn't get good image using by X-ray
Please answer me if knows anyone.

 
20:06 Apr-12-2017

James Scalf

NDT Inspector,
Royal Canadian Air Force,
Canada,
Joined Oct 2012
265
Re: Safe Working Distance for Radiography In Reply to Anto jeyson at 16:44 Apr-12-2017 .

Anto,

There are a number of things that could have occurred. Without knowing what your set up was and what you were shooting as well as the basic parameters of your X-Ray unit (such as kV, mA, time of your exposure, Distance of X-Ray source to part, distance X-Ray source to imaging plate, distance of part to imaging plate, Focal spot size of your X-Ray source and if any screens or filters were used and what shielding you used behind the imaging plate) it is hard to simply state one specific reason why you had such a difference. Simply switching from one excitation source to another in Computed Radiography is not as simple as it is in conventional film as the phosphor imaging plates are more sensitive to a variety of external things.

Please provide more information so we can make a better determination of what may or may not have gone wrong. Cheers...

James

 
00:22 Apr-13-2017

Uwe Zscherpel

R & D,
BAM Berlin,
Germany,
Joined Jan 2010
67
Re: Safe Working Distance for Radiography In Reply to James Scalf at 20:06 Apr-12-2017 .

Dear Anto,
If you are using Ir-192 its clear that you do not provide any details on X-ray voltage or currect, because you are using an isotopic source and its spectrum is fixed by the physics of gamma decay.
But nevertheless, details on the applied imaging plates,used cassettes and means for back scatter protection are missing in your questions. Please provide these details to be able to help you. Did you check ISO 17636-2:2013 to find hint on correct screen material and thickness as well as shielding requirements? These are different theh with film. Did you also joined a suitable training course for industrial CR to learn about dififernt approaches between film and digital?
A typical problem with CR is than you need to cover lead screens used for back scattershielding by a copper of steel screen near top the cassette, because the IP is very sensitive to the X-ray fluorescense leaving the surface of lead screens. This is different to film.
In general, the image unsharpness will increase with the energy for each radiation detector.
Best regards
Uwe Z.

 
11:12 Mar-21-2018

Laurent

Consultant,
France,
Joined Mar 2016
16
Re: Safe Working Distance for Radiography In Reply to Denver at 07:15 Apr-17-2015 .

Denver,

You have written something of very important:
To consider the dose during 1 hour and not to calculate the dose by 1 hour.
Calculation of the distance shall take the operational conditions: number of shoot, direction, area of the shoot... At least the time of exposure and the number of shoot to be considered. Not easy or impossible to calculate precisely the dose in 1 hour.
Necessary to confirm by recording the dose during the working day at the safe separation distance.

 
12:12 Jun-28-2018
azeez khalifa
Re: Safe Working Distance for Radiography In Reply to Mathias at 00:45 Jun-20-2005 .

dear sir
can you explain to me haw can i calculate the safe distance for 300 kV 5 mA I want exact formula i can masseur it by survey neater but my client ask for the actual formulas , i have for gamma ray but i cant fund any thing for the x ray
thanks.

 
13:50 Jun-28-2018

William A Jensen

Other,
IHI Southwest Technologies, Inc.,
USA,
Joined May 2017
30
Re: Safe Working Distance for Radiography In Reply to azeez khalifa at 12:12 Jun-28-2018 .

The exposure rate from a point source of radiation is inversely proportional to the square of the distance. In other words, increasing the distance by a factor of 2 will decrease the exposure by a factor of 4. This concept can be summarized using the inverse square law.
I1D12 = I2D22
I = radiation dose rate
D = distance
Example: If the exposure rate is10 mR/hr at one foot from a radiation source,
what is the exposure rate at 2 feet?
I1D12 = I2D22
(10mR/hr) x (1 foot)2 = (?) x (2 feet)2
10 = 4x
x = 2.5 mR/hr

Additional explanations here:
https://www.nde-ed.org/EducationResources/CommunityCollege/Radiography/Physics/inversesquare.htm

 
13:16 Jul-02-2018

P. M. Mahesh

India,
Joined Nov 2017
2
Re: Safe Working Distance for Radiography In Reply to William A Jensen at 13:50 Jun-28-2018 .

Dear All - Concerned with Safe Working Distance for Industrial Radiography:

'Necessity is the mother of invention' - as they say.

M/s. SafeRad Ltd., based in the UK has invented, designed and manufactures 'SafeRad Radiography system' for industrial radiography testing and evaluation applications, where-in the safe working distance required is only 1.5 to 2 meters from the radiography source set-up, irrespective of the source strength. The technique is popularly known as 'Close Proximity Radiography' or 'Controlled Area For Radiography Testing'.

It is widely used in the oil & gas sector - refineries, petrochemical plants etc...and has proved its worth during plant shut-down and revamp operations, wherein you have many people working round the clock and to evacuate them during radiography would be counter productive and very expensive to the construction companies.

'SafeRad Radiography system' overcomes all the problems and dis-advantages associated with radiation safety and provides high quality radiographs using both the conventional film medium and /or digital medium, without any disruption to the on-going construction schedules in the near vicinity of the radiography location.

If interested, you may contact me on my e-mail id pmmahesh11@gmail for more information on 'SafeRad Radiography system'

Thank you



 


© NDT.net - The Web's Largest Portal of Nondestructive Testing (NDT) ISSN 1435-4934

Open Access Database, |Conference Proceedings| |Articles| |News| |Exhibition| |Forum| |Professional Network|