Ammonia-caused cross-sensitivities when using short-term detector tubes for formaldehyde after disinfection of rooms

Status:

completed 07/1998

Aims:

In accordance with the German provisions for hazardous substances TRGS 522 "Disinfection of rooms with formaldehyde", rooms formerly exposed to formaldehyde must not be used before the atmospheric concentrations of formaldehyde and ammonia remain below 0.1 ml/m³ and 10 ml/m³ respectively. Indoor air measurements by use of short-term detector tubes are permitted on condition that the latter ensure the reliable and indisputable measurement of the above limit value for formaldehyde. The project, initiated by the institution for statutory accident insurance and prevention in the health and welfare services, was aimed to investigate whether or not the colour reaction of the detector tubes is affected by the presence of ammonia, which might entail a falsely reduced indication of concentration, depending on the reaction type of the formaldehyde tube.

Activities/Methods:

Two basic types of tubes in terms of reaction mechanism can be distinguished among the presently marketable detector tubes for formaldehyde with a measurement range from 0.1 ml/m³ to 5 ml/m³: reaction with hydroxylamine phosphate (type 1) and condensation with aromates under extremely acid conditions (type 2). Under defined climatic conditions (20°C, 50% r.h.) detector tubes from different manufacturers were loaded - both simultaneously and successively in changing orders (preconditioning) - with test gas mixtures containing formaldehyde and ammonia. To determine the measurement result, the concentration value of formaldehyde was read on the indicator scale of the tubes following the manufacturer's instructions.

Results:

The reaction of tube type 1 is strongly affected by ammonia concentrations < 10 ml/m³. Consequently, the determined formaldehyde concentrations are falsely reduced. In the case of higher ammonia concentrations (> 50 ml/m³) the specific colour reaction is completely disturbed. Detector tubes of type 2, in contrary, do not show any cross-sensitivities with ammonia for the analysed concentration range of formaldehyde. This tube type can therefore be considered a suitable measuring method in connection with room disinfection. In the light of the project results, TRGS 522 will be supplemented by corresponding information and recommendations concerning the use of formaldehyde detector tubes.

Further informations:

Last Update: