Photo: Gogerr · CC BY-SA 4.0St. Marys’ hazards at a glance: a low wildfire record and 12% of area homes over the radon guideline
The burned-area map is nearly blank around St. Marys, 0% within 25 km since 1986, 0.000% a year. Seismic risk in St. Marys sits near the middle: $0.017 of expected damage per $1,000 of buildings a year, the typical town $0.030. St. Marys grades B− for hazard risk; wildfire is low here, so it earns no credit.
What stands out about St. Marys’s hazards
Four national sources, each read for St. Marys: earthquakes, radon, past fires and flood studies.
What St. Marys faces
Each hazard against its own yardstick; meters run from low to high on that yardstick.
Wildfire
Earthquakes
Radon
Flood study
St. Marys grades B− for hazard risk
Seismic risk and radon set St. Marys’ grade, wildfire can drag it down, and flood mapping stays out of it.
Its place: #646 of 866 in Ontario and #1,578 of 2,589 Canadian towns.
How sure: The seismic figure is a long-run average from NRCan’s model, not a prediction. Small fires and grass fires are largely missing from the national burned-area record.
Wildfire is rare near St. Marys: 0% of the land within 25 km burned since 1986, 0% within 5 km
Past fire around St. Marys’ homes, from the national burned-area record, with the fuel within 5 km.
The yearly burn rate around St. Marys is 0.000%, low beside 0.000% for the typical Canadian town.
With 1.2% forest fuel within 5 km and 0.7% within 25 km, the land around St. Marys gives a fire little to burn.
Shares of land within 5 and 25 km of populated blocks: burned at least once in 1986–2025 (CWFIS burned-area composite), forest fuel and grass (fire behaviour fuel types, 2026, 250 m grid).
Burn rate a year, towns in Ontario · highest of 871
Of the 871 towns in Ontario, 638 have a burn rate that rounds to zero, St. Marys among them; Sioux Lookout leads at 0.16% a year.
Each bar: the yearly average share of land within 25 km of a town’s homes that burned, 1986–2025 (CWFIS); the seven highest towns of 2,500 people or more.
Most of the country’s 2,610 towns are low-band (92%, against 7.5% above); around St. Marys, burning rounds to zero.
Bands of the yearly burn rate: low under 0.05%, moderate under 0.25%, high under 1%, very high 1% or more; towns of 2,500 people or more.
Fire danger and active fires (CWFIS)
Canadian Wildland Fire Information System: National Burned Area Composite 1986–2025 and fire behaviour fuel types (2026), Natural Resources Canada. Measured within 25 km and 5 km of each populated dissemination area; past fire, not a forecast.
The flood map inventory lists nothing for St. Marys
What Canada’s Flood Map Inventory lists for St. Marys: who studied flooding and where to see their maps.
Canada’s Flood Map Inventory lists no study whose area touches St. Marys, which doesn’t mean it has never been mapped.
Towns with a flood study on file
St. Marys has no flood study on file, though 69% of towns in Ontario do (Canada: 58%).
NRCan Canada Flood Map Inventory: a study footprint touching the town’s boundary; towns of 2,500 people or more.
Flood studies don’t enter the grade; they are listed so you can open the official map for St. Marys.
The inventory’s own caution (NRCan): “The Canada Flood Map (CFM) does not include every flood hazard map in Canada and may be incomplete or contain inaccuracies. It should not be relied upon as the official source of flood mapping information. Furthermore, if a map appears to be missing, this does not necessarily mean that the area has never been mapped. For the official version of a map, updated information, or confirmation of applicable regulations, please contact the local authority responsible for flood mapping.”
Expected shaking damage in St. Marys: $0.017 a year per $1,000
Expected yearly building losses from earthquakes, from Natural Resources Canada’s model.
0.6 times the typical $0.030: St. Marys’ $0.017 is ordinary.
Shaking damage a year per $1,000 of building value
Below the middle in Ontario: St. Marys’ $0.017 against a median of $0.043; Alexandria has $0.21.
NRCan seismic risk model (2022): mean yearly building loss per $1,000 of value; medians of towns of 2,500 people or more.
Most of Canada’s 2,611 towns (70%) face more earthquake damage than St. Marys.
Each column: the share of Canada’s towns of 2,500 people or more in that range of yearly loss per $1,000 (NRCan, 2022).
The loss is to St. Marys’ buildings alone, from ground shaking; infrastructure and secondary hazards are left out.
Natural Resources Canada, Canada’s Seismic Risk Model (2022), by census subdivision (2016 boundaries; a few 2021 subdivisions take their residents’ mean).
Radon runs high around St. Marys: 12% of tested homes over the guideline
Long-term radon tests in homes across the survey area, against Health Canada’s guideline.
St. Marys’ area, at 12%, is above the 6.6% of the typical Canadian town, so testing is worth more here than most places.
Tested homes over 200 Bq/m³
Over 600 Bq/m³
Around St. Marys, 12% of tests were over 200 Bq/m³ and 0.9% over 600, against a median of 4% in Ontario.
Health Canada radon survey (2009–2011), by 2007 health region; medians of towns of 2,500 people or more.
The 10–20% band holds 22% of Canada’s 2,611 towns, St. Marys among them; 4.6% rank above.
Each bar: the share of Canada’s towns of 2,500 people or more whose survey area had that share of tests over 200 Bq/m³.
The survey sampled homes around St. Marys; it can’t tell you your basement’s level.
Health Canada, Cross-Canada Survey of Radon Concentrations in Homes (2009–2011). · Area behind the radon tests figures: the Perth District Health Unit
Weather and fire alerts for St. Marys
Alerts for St. Marys come from Environment and Climate Change Canada and, for emergencies, Alert Ready.
| Alert | What it means |
|---|---|
| Warning | Severe weather is happening or about to: act now. |
| Watch | Conditions favour severe weather: be ready. |
| Advisory | Weather that is less severe but could disrupt the day. |
| Special weather statement | Unusual weather worth knowing about. |
| Special air quality statement | Poor air, often wildfire smoke. |
Evacuation orders for St. Marys come from the municipality or the province, while CWFIS maps fire danger every day.
Weather alerts (ECCC) · Alert Ready · Fire danger and active fires (CWFIS)
Hazards in the places around St. Marys
Wildfire band, earthquake risk, radon and flood studies for each place nearby.
| Town | Wildfire | Quake $/1,000 | Radon | Flood study |
|---|---|---|---|---|
| St. Marys | Low | $0.017 | 12% | None listed |
| Perth South 4,055 · 4.7 km | Low | $0.017 | 12% | None listed |
| Stratford 36,097 · 18 km | Low | $0.022 | 12% | None listed |
Nowhere around St. Marys burns more: Perth South, the closest rival, is low to its low.
Radon is the survey area’s figure, so neighbours in one area share it.
Get ready for what St. Marys faces
Practical steps for St. Marys’ hazards, most pressing first.
- Test for three months in winter.
- Over 200 Bq/m³: fix it.
- Kits are cheap; pros test too.
- Never drive through floodwater.
- Move papers and medicines upstairs.
- Ask whether your street is mapped.
- Clear needles and wood nearby.
- Keep a grab-and-go bag ready.
- In smoke, stay in; filter air.
- Has it had a radon test?
- Ask the municipality for flood maps.
- Are flood and wildfire insured?
What this data can and can’t tell you
- Radon is a survey. The radon share comes from about 14,000 long-term home tests in 2009–2011, pooled for now by the 2007 health region St. Marys sits in.
- Wildfire counts one way. The wildfire figure is the share of land within 25 km of St. Marys’ homes burned each year from 1986 to 2025, past fire rather than a forecast, and it can only lower Risk.
- Earthquakes are modelled. Shaking damage is modelled from the ground, the buildings and the odds of each quake, and published for whole subdivisions such as St. Marys’.
- Flood studies aren’t flood zones. A study’s area can be a whole watershed or province, so being on the inventory says a map exists, not that a home in St. Marys floods.
Questions about flooding and hazards in St. Marys
How is St. Marys’s Hazard risk Grade worked out?
Hazard risk gives St. Marys B−, weighing earthquakes and radon and counting wildfire only against it.
How big is the earthquake risk in St. Marys?
In NRCan’s seismic model, St. Marys’ buildings lose $0.017 per $1,000 of value in an average year.
Does St. Marys flood?
The inventory has 0 studies for St. Marys, and an empty list isn’t a clean bill: the municipality holds any flood maps.
Is radon a problem in St. Marys?
The area’s survey found 12% of 108 tested homes above Health Canada’s guideline, so a three-month test is worth doing in St. Marys.
Is St. Marys at risk of wildfire?
No meaningful wildfire history near St. Marys: 0% of nearby land since 1986, band low.
Seismic risk: Natural Resources Canada. Radon: Health Canada. Wildfire: Canadian Wildland Fire Information System. Flood studies: Natural Resources Canada, Canada Flood Map Inventory. Contains information licensed under the Open Government Licence – Canada.
Sources: NRCan, Canada’s Seismic Risk Model 2022 · Health Canada, Cross-Canada Survey of Radon Concentrations in Homes · CWFIS, National Burned Area Composite and FBP fuel types · NRCan, Canada Flood Map Inventory. Under the Statistics Canada Open Licence.
Adapted from Statistics Canada (Census of Population 2021, population estimates 2025, 2021 census boundaries) under the Statistics Canada Open Licence; this does not constitute an endorsement by Statistics Canada. Neighbourhood names in some cities © OpenStreetMap contributors (ODbL).