According to radon mitigation standards, radon mitigation systems should be installed as what type of systems in a building?

Radon mitigation systems are designed to effectively reduce radon levels in a building and, as such, should be installed as permanently integrated systems. This means that the mitigation system becomes an integral part of the building structure to ensure consistent performance and ongoing radon level management.

Permanently and integral systems are important because they provide stability and reliability in long-term radon control. These systems work continuously to mitigate radon gas seepage from the soil into the building. Their permanent nature ensures that they are always in place to combat radon exposure, and they are typically designed to work without requiring removal or disconnection for normal building use.

In contrast, the other options suggest systems that are either temporary, removable, or external, which could lead to lapses in radon control or require additional maintenance and reinstallation. Such inadequacies could cause fluctuations in radon levels, which is not acceptable for health and safety standards concerning radon exposure.