Guide for Radon Measurements in Public Buildings

7. Measurements in Schools

7.1 Measurement Strategy

Schools represent special cases in that they may only be occupied for the school year (approximately 10 months), and the heating and ventilation systems may operate differently at different times throughout the day and night and repair or service work may be in progress when the school is not occupied. All these conditions can affect radon levels during a measurement period. To obtain a representative estimate of student exposure may require measurements to be made only while the school is in session. In addition, an adjustment to correct for day-time exposure (school hours only) may be required for follow-up (see 7.3 for details). Minimizing radon exposure to children at school (since they will spend much time there during their formative years), could serve to reduce their potential overall lifetime exposure.

Health Canada recommends the placement of long-term detectors in schools, where possible, for a minimum testing period of 3 to 10 months (10 months is optimal) during the school year.

7.2 Measurement Location in Schools

To provide a representative estimate for the school-time radon levels, measurements should be made in the lowest-level occupied (occupied by an individual for more than 4 hours per day) classrooms or offices 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. A room is the space enclosed by walls that reach the ceiling. A room subdivided by partitions can be treated as one room. For larger rooms, one detector should be placed for every 200 m2 of floor space.

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

• The preferred device location is by an interior wall at a height above the reach of most pupils: 2.5 to 3 m (8 to 10 feet) from the floor, however, at least 50 cm (20 inches) from the ceiling and more than 20 centimetres (8 inches) from other objects. Depending on the detector used, this may be accomplished by suspending the detector from the ceiling.
• The primary purpose of testing is to assess the level of radon to which the 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 school. Particular attention should be paid to rooms above crawl spaces, over slabs or built into the side of a hill with wall that may be in contact with earth.
• For a complex of buildings comprising a school, each building should be tested separately.
• Measurements should not be made in bathrooms, 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 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.

School boards 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 school, care should be taken to ensure an appropriate number of quality control measurements (duplicates) are made as well, as described in section 6.2.

7.3 Follow-Up Measurements in Schools

It is expected that follow-up measurements will be made in the rooms where the highest concentrations are found, especially when the results exceed 200 Bq/m3. This is done with an active continuous radon monitor that has the capability to integrate and record a new result at least hourly. Follow-up measurements using the monitor must be for a minimum of 48 hours and a 7-day test is preferred. The shorter 48-hour test may give unstable radon results from varying weather conditions. The longer follow-up test (7 days) is more likely to average out this effect. The purpose of the follow-up measurement is to indicate if the long-term measured radon concentration is a realistic estimate of the concentration while the pupils are present.