A practical approach to integrated indoor air mitigation: Graph invariants correlation and subfloor-ventilation lab tests

Radon as an indoor air pollutant has been extensively researched worldwide over the past thirtyyears. However, radon is only one of several other important pollutants present in the indooratmosphere. In addition to radon as an ubiquitous indoor pollutant, the simultaneous presence ofother non-radiological pollutants, such as toxic alkanes found in the working environment, needs tobe accounted for its integrated mitigation approach. Application of graph theory facilitates thestudy of these chemicals, using different relations (linear, logarithmic, polynomial, power andexponential) between graph invariants and the properties under study. In comparison to radon, dataon exposure levels, inhalation dosimetry, and potential health effects for these non-radiological airpollutants is rather limited. This leads to a dissatisfactory situation with regard to mitigating theindoor environment: on the one hand there is the growing awareness for the need of an integratedapproach to indoor mitigation, accounting for the relevant contribution of various pollutants; on theother hand, there are severe constraints in terms of manpower and financial resources, limiting theextent to which these non-radiological pollutants can be researched, when the public health policiesrequire practically implementable advice in the near future.In recognition of these predicaments a new pragmatic approach was taken:a) a screening method was developed for assessing the potential of a suspected pollutant toinduce health effects using graph invariants correlation analysis (GICA);b) a simulation method was developed for conducting simplified tests on the widely usedsubfloor-ventilation technique under defined laboratory conditions, simulating the subsoilpipesystem with an automated soil-filled test chamber (ASTC). The ASTC is equipped withmultiple sensors and externally controlled mechanical ventilation.GICA was applied to seven alkanes found in the working environment (butane, pentane, hexane,octane, nonane, cyclohexane, trimethyl benzene). There is satisfactory correlation (r>0.7) betweenthe different graph invariants and the threshold limit value-time weighted average concentration(TLV-TWA). The ASTC-experiments demonstrated the capability of this laboratory-system toallow a prediction of the performance characteristic for a given subfloor-ventilation system andcertain environmental conditions.