Over What Area Is the Contamination Rate Calculated?

Who this page is for, and what it answers

The contamination rate is calculated over an area set by table 3 in article 11: 1000 square centimetres for floors, walls and ceilings, 300 for materials, equipment and tools, 300 for the hands taken in full, and 100 for the rest of the body. A reading in becquerels per square centimetre is incomplete without an area.

Three words are needed before the table. The becquerel is the unit of radioactive activity. A becquerel per square centimetre means activity spread over an area of surface, so it cannot be read without a known area. And the calculation area is the area the measured activity is divided by, not the area of the contaminated patch.

You take the reading and divide it by a stated area from the table. The result is a rate that is then compared with the limit.

The table is titled as calculations of the contamination rate by area. Its two column headings are the contaminated area and the area figure. It has four rows: floors, walls and ceilings; materials, equipment and tools; the hands; and the rest of the body.

The most important caution: the hands row is unlike the others. The other three are calculated for each stated area separately. The hands, by contrast, are calculated as a whole area.

Taking each area separately means the survey is divided into squares. Each square is read on its own and compared with the limit on its own. The contamination of a wide floor is not totalled and then divided over its whole area. That would hide a severe patch inside an otherwise clean floor.

This page gives no limit. The limits are in tables 1 and 2, each with its own page in this batch. This table gives the denominator you divide by. It is half of the calculation, and the limit is the other half.

The rows of the table as the decision states them

The first row covers floors, walls and ceilings. The figure given in it is 1000 square centimetres, applied to each such area separately. The reliable figure is 1000 square centimetres. Its equivalent in square metres is 0.1, which is our reading and not a transcription from the text.

The second row covers solid materials, equipment and tools. The figure given in it is 300 square centimetres, applied to each such area separately. The reliable figure is 300 square centimetres. Our reading of its equivalent is 0.03 square metres.

The third row covers the hands. The area is stated as 300 square centimetres, calculated in full. The number 300 is the same as the row above it, but the wording differs. Here it is calculated as a whole, and the words for each do not appear.

The fourth row covers the rest of the body. The figure given in it is 100 square centimetres, applied to each such area separately. The reliable figure is 100 square centimetres. It is the smallest calculation area in the table.

What falls outside this table

Table 3 carries no permitted limit. Anyone looking in it for an acceptance figure will not find one. The limit sits elsewhere in the instructions.

It does not deal with clothing as such. Clothing is a row in table 1. Worn and movable items are named in the scope of table 2. We do not stretch a row from one table into another.

Nothing in this table, or in the other places we have read, sets a penalty or a period for coming into line. On the parts we have not read we pass no judgement.

The table does not state how a smear is taken. Direct and indirect surveying sit in another article of the instructions. That is the subject of a later batch in this series. We name it and do not quote it here.

The table does not say who takes the measurement. This page is about the calculation, not about the duties. Skin and parts of the body appear here as a matter of calculation, not of treatment. A later batch in this series covers the article dealing with personal contamination and the referral it triggers. Skin is never judged by borrowing a surface rule.

Table 3 restated, with our square metre reading

The table below sets each kind of place against its calculation area. Skip it on a first reading, and come back to it when you calculate.

The third column in our table is our reading, not a transcription from the text. The square metre figures appear in the transcribed original in a disordered form. So we transcribe the square centimetres and attribute the square metres to ourselves.

A worked case, and four practical steps

Suppose contamination on both hands of a worker in a laboratory, with the survey taken over the hands. The area it is divided by is 300 square centimetres in full. Had it been divided by 1000, the rate would appear at about a third of its true value. That is an error of reading the wrong row, not an instrument error. What a single palm takes of that figure the text does not set, and we see that as an open point.

Step one: identify the place first, a floor, a tool, a hand, or the rest of the body. The row follows the area, not the instrument.

Step two: use the area given in the row and do not widen it. Widening the area hides an exceedance.

Step three: read the wording of the hands row itself. It is one whole area, not an area repeated for every 300 square centimetres. This is the distinction most often missed.

Step four: write the area used in the report beside the figure. A rate without an area is a number that cannot be reviewed. We train people to choose the area and record it, and the calculation itself stays the protection officer's work.

Questions people ask

Notes on transcription and reading

This table contains the second of the transcription points we hold in reserve. What is reserved is the square metre form alone. The square centimetre values are transcribed without reservation.

This reservation and the one in table 2 differ in effect. The reservation in table 2 blocks giving a becquerel figure. The reservation here blocks nothing, because the reliable values suffice for the calculation.

Left open in the text: the table does not say how a contaminated patch smaller than the row's area is treated. We have not asked the competent authority about it, so we ascribe them no position.

What the institute offers, its limits, and the reference

This page is about the areas used to calculate the contamination rate. The institute trains people to choose the right area and to document it in the report.

ALDuha Institute for Training and Environmental Consulting works in training and consulting. Its training is licensed. It does not run a laboratory analysis service for smears. It does not calibrate radiation survey instruments. It does not test equipment or certify it as safe. It does not carry out decontamination in a laboratory or on a site.

Surveying and decontamination are the work of the licence holder and his radiation protection officer. Where outside expertise is needed, it is arranged through specialist partners. We train people to read, measure and document. We do not do the work in place of the licence holder.

Neither our training nor our consulting gives any undertaking that a licence will be issued. There is no undertaking about how long an approval will take. That decision belongs to the competent authority alone.

Reference: decision 3 of 2007 of the chairman of the Supreme Council for the Environment and Natural Reserves, on radioactive decontamination instructions. Location: table 3 in article 11 of the attached instructions. The decision rests on decree law 31 of 2002, in particular its article 17, and on the executive regulation issued by decision 4 of 2003, in particular its article 97.

A note on the names of authorities: the decision was issued by the Supreme Council for the Environment and Natural Reserves. The authority addressed today is the Ministry of Environment and Climate Change, which houses the Radiation Protection Department. The name changed and the duty stands.

This page is an introductory explanation of a published text, and is not a legal opinion. It does not replace reading the decision itself. It does not replace checking with the competent authority.