Sheltering in place is thought to be an effective protective action in the case of releases of radioactive dusts and gases from nuclear sites because it reduces gamma radiation dose by a combination of shielding and distance and it reduces the inhalation dose while the airborne levels are higher outside than in. If you are going to stay in shelter for any length of time with elevated external levels it is obviously better to reduce air exchange between the inside and outside.
The UK national advice on the topic has “Key factors affecting the effectiveness of sheltering-in-place include: the air permeability of a building used for shelter; the meteorological conditions; the particle size distribution; the effectiveness/timing of opening windows and doors; and the release duration, all of which could vary significantly from one scenario to another (or even within a single scenario). Some of these factors such as meteorological conditions are time dependent, and therefore the DRF may vary as a function of time.” (PHE-CRCE-049)
Advice to the public in the UK is provided by REPPIR Prior Information leaflets and websites for those near to nuclear sites. These tend to have the advice to close doors and windows and will then say something about other steps that can be taken to reduce air exchange. Examples:
Barrow: “Switch off fans, heating systems, air conditioning and put out open fires”.
Capenhurst: “Switch off all heating systems. Ventilation fans and air conditioning systems to avoid drawing in outside air”.
Devonport: “Put out fires and boilers and shut off air conditioning units. Fans, air conditioning units, boilers, gas fires and heating systems draw in air from outside. You should switch off these things (and damp down open fires) to stop radioactive material from outside coming inside”.
EDF sites “close all outside doors and windows, switch off any ventilation or extractor fans”. [No mention of heating!]
AWE “Turn off boilers and air conditioning units and put out fires or woodburners. Fans, heating systems, boilers, gas fires and air conditioning all draw in air from outside so these should be shut down to minimise radioactive particles entering buildings”.
While the physics suggests that air exchange between the outside world and the inside of a building is affected by the temperature difference most of the historic concern, I suspect, is with systems that burn hydrocarbons in-situ and are designed to draw in air to support combustion. Not everybody uses such systems these days.
Are there forms of heating that we can use safely while in shelter – electric panel convection heaters or air source heat pump serving underfloor or ceiling mounted fan coil units that don’t obviously rely on external fresh air or do we all have to freeze while waiting for the all-clear or evacuation instructions?