Photo: P199 · CC BY-SA 3.0Sarnia is on Canada’s flood inventory: 1 listed, led by St. Clair Region Conservation Authority
Since 1986 almost nothing has burned near Sarnia: 0% of the land within 25 km, or 0.000% a year. Earthquakes matter little: NRCan’s model puts building losses at $0.015 a year per $1,000 of value, against $0.030 for the typical town. Radon is about average around Sarnia: 8.4% of tested homes in the survey area topped the guideline, against 6.6% for the typical town. Hazard risk gives Sarnia a grade of B+, from earthquakes and radon alone.
What stands out about Sarnia’s hazards
Four national sources, each read for Sarnia: earthquakes, radon, past fires and flood studies.
What Sarnia faces
Each hazard against its own yardstick; meters run from low to high on that yardstick.
Wildfire
Earthquakes
Radon
Flood study
Sarnia grades B+ for hazard risk
The grade weighs Sarnia’s seismic risk and radon equally, and wildfire is one-sided: a high band counts against a town, a low one earns nothing.
Its place: #478 of 866 in Ontario and #926 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.
Few fires near Sarnia: 0% within 5 km, 0% within 25 km
Past fire around Sarnia’s homes, from the national burned-area record, with the fuel within 5 km.
Next to the typical Canadian town (0.000% a year), Sarnia’s 0.000% is in the low band.
With 0.8% forest fuel within 5 km and 0.2% within 25 km, the land around Sarnia 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
Among the 871 towns in Ontario, Sioux Lookout burns fastest (0.16% a year); Sarnia is with the 638 near zero.
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.
The low band holds 92% of Canada’s 2,610 towns, and Sarnia sits at its very bottom; only 7.5% are above it.
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.
Sarnia is on the flood map inventory: 1 study, by St. Clair Region Conservation Authority
What Canada’s Flood Map Inventory lists for Sarnia: who studied flooding and where to see their maps.
St. Clair Region Conservation Authority studied flooding in an area that includes Sarnia (2009); open its map to see which streets lie in a flood zone.
| Study | By | Year | Status |
|---|---|---|---|
| SCRCA Floodplain Estimation Study for Ontario Regulation 171-06 | St. Clair Region Conservation Authority | 2009 | final · not public |
Towns with a flood study on file
Its flood study puts Sarnia with 69% of towns in Ontario; Canada’s share is 58%.
NRCan Canada Flood Map Inventory: a study footprint touching the town’s boundary; towns of 2,500 people or more.
Listed, not scored: a flood study proves a map exists, not that Sarnia floods.
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.”
Natural Resources Canada, Canada Flood Map Inventory; links go to each study’s owner.
Little shaking expected in Sarnia: $0.015 a year per $1,000
Expected yearly building losses from earthquakes, from Natural Resources Canada’s model.
0.5 times the typical $0.030: Sarnia’s $0.015 is low for Canada.
Shaking damage a year per $1,000 of building value
Below the middle in Ontario: Sarnia’s $0.015 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.
Earthquakes cost less around Sarnia than in 72% of Canada’s 2,611 towns.
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 model counts damage to Sarnia’s buildings and their occupants from shaking only: not liquefaction, landslides, tsunami or fires after a quake.
Natural Resources Canada, Canada’s Seismic Risk Model (2022), by census subdivision (2016 boundaries; a few 2021 subdivisions take their residents’ mean).
Some radon around Sarnia: 8.4% of area homes over the guideline
Long-term radon tests in homes across the survey area, against Health Canada’s guideline.
Sarnia’s area, at 8.4%, is close to the 6.6% of the typical Canadian town.
Tested homes over 200 Bq/m³
Over 600 Bq/m³
Around Sarnia, 8.4% of tests were over 200 Bq/m³ and 0.6% 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.
Sarnia is in the 5–10% band with 37% of Canada’s 2,611 towns; 26% have more.
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 share describes the area, not a house: in Sarnia as anywhere, test to be sure.
Health Canada, Cross-Canada Survey of Radon Concentrations in Homes (2009–2011). · Radon tests: one figure for all of the Lambton Health Unit
Weather and fire alerts for Sarnia
Alerts for Sarnia 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. |
Alert Ready carries evacuation orders for Sarnia to phones; CWFIS shows the day’s fire danger.
Weather alerts (ECCC) · Alert Ready · Fire danger and active fires (CWFIS)
Hazards in the places around Sarnia
Wildfire band, earthquake risk, radon and flood studies for each place nearby.
| Town | Wildfire | Quake $/1,000 | Radon | Flood study |
|---|---|---|---|---|
| Sarnia | Low | $0.015 | 8.4% | Yes |
| Point Edward 1,989 · 3.6 km | Low | $0.016 | 8.4% | Yes |
Nowhere around Sarnia burns more: Point Edward, 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 Sarnia faces
What to do about the hazards Sarnia faces, and what to ask before you buy.
- 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?
- Check the address on the flood map.
- Are flood and wildfire insured?
What this data can and can’t tell you
- 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 Sarnia floods.
- Wildfire counts one way. Wildfire is read from the national burned-area record around Sarnia’s homes since 1986, a history of fire that may lower Risk but never raises it.
- 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 Sarnia sits in.
- Earthquakes are modelled. NRCan models what earthquakes would cost buildings each year on average, subdivision by subdivision; Sarnia’s figure is its subdivision’s.
Questions about flooding and hazards in Sarnia
Does Sarnia flood?
Sarnia’s area has been studied for flooding, and the owner’s map shows which streets lie in a zone; the grade leaves flood out.
Is radon a problem in Sarnia?
Around Sarnia, 178 survey homes were tested and 8.4% came in over 200 Bq/m³, a guide to the area, not to any one home.
Is Sarnia at risk of wildfire?
Very little by the national record: Sarnia’s band is low, with 0% of the land within 25 km burned since 1986, so wildfire doesn’t change its grade.
How is Sarnia’s Hazard risk Grade worked out?
Sarnia grades B+ for hazard risk, from earthquakes and radon, with wildfire counted only where it lowers the grade.
How big is the earthquake risk in Sarnia?
NRCan’s model expects shaking to cost buildings in Sarnia $0.015 a year for every $1,000 of their value, on average over many years.
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).