Guide for Radon Measurements in Public Buildings

6. Measurement in Homes

6.1 Measurement Strategy

Buildings with a high occupancy of long duration by the public, such as hospitals, long-term care residences, correctional facilities, schools and daycare centres are "public buildings" and the Radon Guideline applies.

Buildings where the occupants are employees are "workplaces", and the exposure to radon is governed by different guidelines and regulations, such as the Canadian Guidelines for Management of Naturally Occurring Radioactive Materials (NORM) and the Canada Labour Code.

Measurements in public buildings provide a different set of challenges from homes. Hospitals, long-term care residences and correctional facilities are occupied continually, and so a long-term measurement will give a good estimate of the radon exposure of the occupants. As most schools may only be occupied during the day, five days a week, for the school year only (approximately 10 months) a different approach normally is used (see Section 7).

Health Canada recommends the placement of long-term detectors in a public building (hospitals, long-term care facilities, correctional facilities and daycare centres) for a minimum testing period of 3 to12 months (12 months is optimal).

6.2 Measurement Locations

Public buildings differ from houses in that the occupants are not usually directly involved in the measurement process. The choice of the measurement device location is constrained by the need for security so that the devices are not readily accessible by curious occupants. The buildings usually contain many rooms. A room is the space enclosed by walls that reach the ceiling. A room subdivided by partitions can be treated as one room.

To provide a representative radon concentration estimate for the building, measurements should be made in the lowest-level occupied (occupied by an individual for more than 4 hours per day) rooms of the building, preferably at the same time. A radon measurement should be made in each room occupied in a basement, or if no basement exists, on the ground floor or the floor with the lowest-level occupied rooms. For larger rooms, one detector should be placed for every 200 m2 of floor space.

The measurement location should be selected so that there is a reasonable expectation that the measurement device will not be disturbed during the measurement period.

• The preferred device location is by an interior wall at a height of 0.8 m to 2 m (3 to 6.5 feet) from the floor in the typical breathing zone, however, at least 50 cm (20 inches) from the ceiling and 20 centimetres (8 inches) from other objects so as to allow normal airflow around the detector. Depending on the detector used, this may be accomplished by suspending the detector from the ceiling. Detector should be placed approximately 40 cm (16 inches) from an interior wall or approximately 50 cm (20 inches) from an exterior wall.
• The primary purpose of testing is to assess the level of radon to which occupants are exposed. Therefore, areas should not be chosen to test where occupants do not spend much of their time. Efforts should be concentrated on testing occupied rooms in basements or if no basement exists, the ground floor or the floor with the lowest-level occupied rooms of the building. Particular attention should be paid to rooms above crawl spaces, over slabs or built into the side of a hill with walls that may be in contact with earth.
• For a complex of buildings, such as a hospital, each building should be tested separately.
• Measurements should not be made in closets, cupboards, sumps, crawl spaces, or nooks within the foundation. Radon concentrations in these areas are not representative of the concentration in the occupied area of the building.
• The device location should not be in air currents caused by heating, ventilating and air conditioning vents, doors, fans and windows. Locations near heat, such as over radiators, near fireplaces or in direct sunlight, should be avoided as some measurement devices may be affected. Similarly devices should not be placed on or near electrically powered equipment or appliances such as the tops of computers, television sets, stereos or speakers.
• Measurements during the warm weather in buildings without central air conditioning are likely to give misleading results due to the very high likelihood that windows will be open during the measurement period. This problem can be reduced by increasing the duration of the test and underscores the importance of a long-term radon measurement.

Building owners should always consider re-testing whenever major renovations are performed that might substantially change the ventilation or airflow in the building or the use of the rooms in the lowest-occupied level.

In cases where more than 10 detectors are deployed in a building, care should be taken to ensure an appropriate number of quality control measurements (duplicates) are made as well. Duplicate measurements should be made at the rate of 10% of the total number of measurement locations (e.g., if 10 detectors are deployed in a building, one duplicate measurement should also be made, if 20 detectors are deployed, two duplicate measurements should also be made, etc.). Duplicate measurements are made by placing two detectors side-by-side (< 10 cm apart or 4 inches). The locations selected for duplication should be distributed systematically throughout the entire population of the sampling. Such duplicate measurements provide a check on the quality of the measurement results and allow the user to make an estimate of the relative precision of the measurements. Large precision errors may be caused by detector manufacture and/or improper data transcription or handling by suppliers, laboratories or persons performing detector placement. If duplicate results differ significantly (results of the two measurements are different by a factor of 2), the problem should be reported to the supplier of the detector and/or the laboratory making the measurement and the cause investigated. The measurements for the room or area in question may have to be repeated based on the outcome of the investigation.

Consideration should also be given to incorporating an appropriate frequency of blanks and spikes into any quality assurance plan associated with radon measurement strategies in schools and public buildings.