What is Radon Gas ?

Radon is all around us as part of our environment - in the soil, the water, and in the air. It is an invisible, natural radioactive gas. It is odourless and tasteless. In order to detect the gas, a measuring device must be used.

Radon becomes a health hazard if it is allowed to accumulate in buildings.

Radon is a proven human carcinogen. In 1988, it was given a Group 1 Classification by the World Health Organization (WHO/IARC Monographs Programme, Vol. 43 1988, p.173) ......

' There is 'sufficient evidence' for the carcinogenicity of radon and its decay products in humans, i.e. a causal relationship has been established between exposure to these agents, the exposure circumstance and human cancer. That is, a positive relationship has been observed between the exposure and cancer in studies in which chance, bias and confounding could be ruled out with reasonable confidence.'

Radon is a major cause, second only to cigarette smoking, of lung cancer deaths.

Radon is not normally considered to be a 'contaminant'.

However, in the case of water supplied to the interiors of buildings, radon must be regarded as a 'contaminant'. Although high concentrations of radon in water have an adverse effect on human health, the radiation dose to the body due to inhalation of radon gas released from the water is usually more important.

Radon must also be regarded as a 'contaminant' in building materials.

Radon Activity & Accumulation

Radon (Rn-222), a chemical element with an Atomic Number of 86 and also a heavy radioactive gas of the Noble Gas Group on the periodic table, is generated by the radioactive decay of Radium (Ra-226).  It is colourless, odourless, tasteless, and with a density (1 atm / 0°C) of 9.73 g/litre is 7.5 times heavier than air, and more than 100 times heavier than hydrogen.  The gas liquefies at -61.8°C, and freezes at -71°C.  Upon further cooling, solid radon glows with a soft yellow light which becomes orange-red at the temperature of liquid air (-195°C).

To prepare concentrated samples of radon gas, a supply of radium is placed within a glass vessel in aqueous solution, or in the form of a porous solid from which the gas can readily flow.  At intervals of a few days, the accumulated radon is pumped off, purified, and compressed into a small tube, which is then sealed and removed.  The tube of gas is a powerful source of penetrating gamma radiation / particles, which comes mainly from one of radon's decay products, Bismuth-214 (Bi-214). In the past, such tubes of radon were used for radiotherapy and radiography.

Examine the Periodic Table of Elements

Natural Radon, however, consists of three isotopes, one from each of the three natural radioactive disintegration series (uranium, thorium, and actinium).  The longest lived isotope, Radon-222 (alpha emitter of 3.823 day half-life), discovered in 1900 by the German chemist Friedrich E. Dorn, arises in the uranium series.  The name radon is sometimes reserved for this isotope in order to distinguish it from the other two natural isotopes, called 'thoron' and 'actinon' because they originate in the thorium and actinium series, respectively.

The gas thoron, Radon-220 (alpha emitter of 55.6 second half-life), was first observed in 1899 by the English scientists R. B. Owens & Ernest Rutherford, who noticed that some of the radioactivity of thorium compounds could be blown away.  The gas actinon, Radon-219 (alpha and gamma emitter of 3.92 second half-life), was found in 1904, independently by Friedrich O. Giesel & Andre-Louis Debierne, to be associated with actinium.

See Table B, Annex I on Page 23 of European Union Council Directive 96/29/Euratom for a listing of the radioactive decay product groupings of U-238, Th-232 and Ra-223.

Adverse Health Effects from Radon (incl. Rn-222, Rn-220, RnD) 

Figure 1  shows  how  two  isotopes  of  natural  radon,  Rn-222  and  Rn-220,  decay  progressively  to  a  series  of   'decay  products'  ( RnD ) .    It  is  these  products,  and  not  the  radon  gas  itself  because  it  is  inert,  which  first  attach  themselves  to  minute  particles  suspended  in  the  air,  i.e.  aerosols,  depending  on  ventilation  in  a  building  space,  and  on  aerosol  size  and  concentration.    A  small  proportion  of  decay  products  will  remain  in  unattached  form. 

A  significant  danger  to  human  health  arises  from  the  inhalation  of  these  continuously  decaying  products,  which  are  carried  by  radon  gas  and  aerosols,  into  a  person's  lungs.    The  radiation  dose  to  lung  tissue  is  dominated  by  alpha  particle  emissions  from  the  decay  products  which  then  become  attached  to  the  lung  linings ;   damage  to  sensitive  cells  is  caused,  and  the  probability  of  cancer  developing  increases. 

When  radon  is  permitted  to  accumulate  in  a  building,  e.g.  in  an  internal  Radon  Vent  Pipe,  a  source  of  penetrating  gamma  particle  radiation  is  created  and  serious  adverse  effects  on  human  health  may  result.    Exposure  to  elevated  levels  of  the  gas  may  also  be  implicated  in  the  occurrence  of  other  cancers,  such  as  leukaemia  in  children. 

As  with  prolonged  exposure  to  the  radiation  from  any  form  of  ionization  activity,  genetic  and  human  fertility  damage  will  occur. 

European Union Legislation

The  1997  Amsterdam  Treaty  (97/C 340/01)  -  Paragraph  3  of  Article  95  of  the  consolidated  version  of  the  Treaty  establishing  the  European  Community  (97/C 340/03)  -  states  ........ 

' The  Commission,  in  its  proposals  envisaged  in  paragraph  1  concerning health,  safety,  environmental  protection  and  consumer  protection,  will  take as  a  base  a  high  level  of  protection,  taking  account  in  particular  of  any new  development  based  on  scientific  facts.    Within  their  respective  powers, the  European  Parliament  and  the  Council will also seek to achieve this objective. ' 

The  relevant  secondary  E.U. legislation  is  Council  Directive  96/29/Euratom ,  of  13^th May  1996,  which  lays  down  basic  safety  standards  for  the  protection  of  the  health  of  workers  and  the  general  public  against  the  dangers  arising  from  ionizing  radiation.    This  Directive  should have been implemented  by  all  Member  States  before  13^th May  2000 (Article 55). 

The  World  Health  Organisation,  in  the  preamble  to  its  Constitution,  defines  'health'  as  ........ 

' a  state  of  complete  physical,  mental  and  social  wellbeing,  and  not  merely the  absence  of  disease  or  infirmity '. 

Therefore,  within  the  European  Union  the  objective  must  be  to  achieve  a  sufficiently  low  level  of  radon,  or  radon  associated,  ionization  activity  in  the  interior spaces and superstructure  construction  cavities  of  all  buildings  -  such  that  a significant  hazard  to  human  health  is  not  posed.  Based  on  the  approach  taken  in  U.S. Federal Legislation,  a  target  human  health  level,  which  lies  within  the  range  of  10 - 40 Bq/m³,  should  be  achieved. 

Harmonized European Vocabulary

Some  National  Approaches  and  Findings ^{[ 1 ]}

In  Sweden,  a  simple  three-fold  radon  risk  classification  for  ground,  based  on  geology,  soil  permeability  and  soil  gas  radon  measurement,  has  been  developed.    This  system,  together  with  airborne  gamma  spectrometry  surveys,  is  used  to  produce  1 : 50,000   'provisional  radon  risk  maps'.    By  1987,  approximately  60%  of  the  country  had  been  mapped.    Where  the  soil  cover  is  less  than  2  metres  thick  over  bedrock  geology  it  is  deemed  to  be  high  risk,  and  ground  measurements  are  made  of  radon  concentrations  even  if  the  airborne  survey  reveals  little  radioactivity.    Detailed  radon  surveys  are  usually  made  before  building. 

The  United  States  is  divided  into  three  zones  indicating  radon  activity  levels  of  less  than  75 Bq/m³,  between  75 - 150 Bq/m³,  and  areas  with  greater  than  150 Bq/m³.    The  Environmental  Protection  Agency,  however,  recommends  that  all  houses  are  tested  for  radon  concentrations,  regardless  of  location  within  the  country,  since  very  high  levels  have  been  found  in  each  zone.    Surveys  of  radon  soil  gas,  for  example,  around  the  city  of  Dunnellon,  in  Florida,  have  ranged  from  2,500  to  338,000 Bq/m³. 

Radon  Measurement  Uncertainty ^{[ 6 ]}

( i )          Variations  With  Time 
Concentration  variations  of  radon  and  its  decay  products (RnD)  occur  on  many  time  scales,  from  hourly  to  annually,  and  depend  on  seasonal  factors  and  weather  conditions,  building  characteristics,  operation  of  building  heating  and  cooling  systems,  building user lifestyles,  source  relative  strength,  etc.    Usually,  concentrations  are  higher  in  the  evening  and  night  than  in  the  late  morning  and  early  afternoon,  and higher  in  the  winter  than  in  the  summer.    However,  it  is  not  yet  possible  to  predict  these  variations  with  accuracy. 

( ii )         Variations  With  Measurement  Duration 
The  longer  the  duration  of  a  measurement  the  lower  in  general  is  its  variability :   individual  very  short-time  measurements  ( ~ minutes  or  a  few  hours )  can  show  variations  higher  than  a  factor  of  10.    Measurements  lasting  a  few  days  generally  show  variations  less  than  a  factor  of  10,  while  the  seasonal  variations  found  in  measurements  of  six  months  duration  are  usually  well  within  a  factor  of  5.    Annual  variations  are  well  within  a  factor  of  2,  e.g.  measurements  carried  out  for  a  5 year  period  in  40  residences  in  Grand  Junction  ( Colorado,  USA )  show  a  mean  coefficient  of  variation  of  approximately  22% .    Because  of  the  magnitude  of  these  variations,  one  year  measurements  are  considered  the  best  compromise  to  estimate  the  'average'  value. 

( iii )        Measurement  Accuracy 
Measurement  detectors / instruments  have  to  be  first  of  all  calibrated,  then  checked  frequently.    Periodic  participation  in  measurement  intercomparisons  is  also  to  be  recommended.    Calibration  measurements  are  usually  performed  in  a  'radon  chamber',  in  which  a  known  quantity  of  radon  is  introduced.    In  general,  the  calibration  of  radon  decay  products  is  more  difficult  than  the  calibration  of  those  for  radon,  due  to  many  reasons,  one  of  which  is  that  there  is  no  primary  standard  for  radon  decay  products. 

( iv )        Measurement  Precision 
Precision  is  assessed  by  replicate  measurements,  i.e.  exposing  many  detectors  at  the  same  time  to  the  same  concentration.    This  allows  an  estimate  to  be  made of  the  coefficient  of  variation  of  the  detectors  at  that  value  of  concentration.    A  periodical  check  on  precision  should  always  be  made. 

In Ireland, for example ...

RPII

Measurement Uncertainty of the standard Alpha Particle Etched-Track Detector distributed by the Radiological Protection Institute of Ireland (RPII) is as follows:

Unfortunately, until the RPII includes proper statements of Measurement Uncertainty
in its Test Reports .... our Architectural Practice ....

• cannot recommend any RPII Radon Testing Services ;
  and
• will not accept any RPII Test Reports as proper evidence of Radon Test results.

See our Technical Guidance Notes.

Some  General  Guidelines  on  Construction  Detailing

( a )         To  Reduce  Radon  Ingress 

• use  low-permeability  building  products  and  materials,  e.g.  solid  rather  than  cavity  concrete  blocks  with  all  vertical  and  horizontal  joints  properly  filled ; 
• ensure  that  all  designed  cavities  are  effectively  gas  sealed  to  indoor  spaces ; 
• use  low-permeability  construction  techniques,  e.g.  in-situ  mass  concrete  with  steel  reinforcement  to  limit  shrinkage / movement  cracking ; 
• avoid  construction  which  has  too  many  joints  or  openings ; 
• design  and  detail  construction  for  controlled  movement ;
• limit  numbers  of  service  penetrations  and  other  openings  in  ground  slabs  ...... design  for  grouping  of  services,  with  effective  radon  gas  seal,  rather  than  allow  an  ad-hoc  approach  on  site  which  cannot  be  controlled. 
  
  
  

( b )         To  Aid  Radon  Dilution / Dispersal 

• radon  vent  pipes ( RVP's )  should  always  be  brought  externally  to  a  proper,  open  terminal  unit,  suitably  located  above  building  roof  level ;
• avoid  downstand  beams  and  limit  number  of  rising  walls  beneath  ground  slabs  which  provide  confined  spaces  for  radon  gas  to  accumulate ; 
• ensure  that  the  hardcore  layer  in  the  sub-floor  construction  is  gas  permeable ; 
• where  appropriate / practicable,  and  in  a  manner  compatible  with  the  energy  conservation  performance  of  the  building   -   maximize  underfloor  ventilation ;
• design  interior  spaces  for  maximum  ventilation,  in  a  manner  compatible  with  the  energy  conservation  performance  of  the  building.