Hazardous Gases on the Farm: A Silent Threat to Safety
Hazardous gases are an often-overlooked danger on farms, lurking in silos, manure storages, anaerobic digesters, grain bins, and any confined space with poor ventilation. They can pose serious health risks to both humans and animals.
Common farm gases include:
- nitrogen dioxide
- hydrogen sulfide
- methane
- ammonia
- carbon dioxide
- carbon monoxide,
Some gases, like nitrogen dioxide and hydrogen sulfide, are especially dangerous because they are toxic and can push out oxygen.
Silo Gas (Nitrogen Dioxide)
Silo gas is mostly nitrogen dioxide (NO₂). It forms during the fermentation process that occurs mainly in the first two weeks after harvest, while silage is fermenting. This gas consumes oxygen and releases carbon dioxide. Under certain conditions—especially when nitrate-rich plant material is present—nitrogen dioxide can also be generated as a by-product. This gas is highly corrosive and toxic and tends to settle in low areas due to its density, making it particularly dangerous in enclosed spaces.
Nitrogen dioxide, even with short-term exposure, can cause severe lung damage or sudden death. It is an asphyxiant that has a bleach-like odour and may appear as a reddish-brown haze. Since it is heavier than air, it tends to settle just above the silage surface and can flow down silo chutes into feed rooms, creating dangerous conditions in confined spaces.
What causes silo gas? Nitrate accumulation in corn is most common when high soil nitrate levels coincide with drought stress, which disrupts normal plant growth. The amount of nitrate in plant material—which contributes to NO₂ formation during fermentation—is influenced by crop management and weather conditions. Rainfall following drought conditions can result in plants taking in a flush of nitrates. After a rainfall, plants resume converting nitrates into protein, resulting in normal nitrate concentrations within a few days.
How to reduce the risk? Harvesting strategies can also help mitigate nitrate risks:
- Wait 5 to 7 days after rainfall that ends a prolonged dry period before harvesting
- Cut corn higher, leaving the lower third of the stalk with the highest nitrate concentrations behind.
- Ensure proper silage fermentation since silage that is too wet or too dry may not ferment properly, resulting in limited nitrate dissipation.
- Avoiding non-protein nitrogen sources (e.g., urea or anhydrous ammonia) in moisture-stressed silage since these N sources can increase the risk of toxic gas formation.
- Ventilate silos and feed rooms by running the forage blower for 30 minutes before entry and keeping it running while inside
Always sample fermented silage for nitrate levels before feeding and manage dietary nitrate intake carefully. Use caution when feeding green chop or grazing moisture-stressed crops, which can expose livestock to elevated nitrate levels.
Manure Gases
The most dangerous gas from manure is hydrogen sulfide (H₂S). It forms when there’s little or no oxygen (anaerobic or oxygen limiting conditions). Risk of the gas can spike during agitation, especially in under-barn storage. Warm weather, poor ventilation and agitation of manure can increase the concentration of hydrogen sulphide.
Hydrogen sulphide is heavier than air and an asphyxiant that interacts with blood hemoglobin to prevent oxygen transport. It has a rotten egg smell, (but you can’t smell it at high concentration levels). Table 1 shows the effect of hydrogen sulphide at specific concentrations.
Table 1: Effects of Hydrogen sulphide on people
| H2S Concentration | Effect on People |
| 4 ppm | Easily detectable smell |
| 10 ppm | Eye irritation |
| 27 ppm | Unpleasant odour |
| 100 ppm | Coughing, eye irritation, loss of sense of smell after 2 – 15-minute exposure |
| 200 – 300 ppm | Eye inflammation and respiratory tract irritation after 1 hour |
| 500 – 700 ppm | Loss of consciousness and possible death within 30 – 60 minutes |
| 800 – 1,000 ppm | Rapid unconsciousness, cessation of respiration and death |
| >1,000 ppm | Diaphragm paralysis on first breath, rapid asphyxiation and death |
| Source: American Society of Agricultural and Biological Engineers, ASABE EP470.1 Oct 2011 (R2016) Manure Storage Safety. | |
Extra risks:
Manure agitation can increase hydrogen sulphide gas (H₂S) to dangerous levels in seconds. Ventilation systems and/or wind effects can cause the gas to move, including up into the barn space towards exhaust fans or an open window. Just as with silage gases, prolonged dry weather can increase the risk of manure gas emissions.
Crust on manure can trap gases. Crusting during dry weather can trap gases, which can then be released in dangerous concentrations during agitation or following a rain event. When rain follows a prolonged dry period, microbial activity increases, leading to a surge in gas production, including methane and hydrogen sulphide.
Gypsum bedding (calcium sulfate) can increase hydrogen sulphide gas (H₂S) production. Recent interest in gypsum for livestock bedding has resulted in increased risk for H₂S emissions during manure storage and application. In anaerobic storages, the microbes can convert the sulphate in gypsum to H₂S.
Safety Tips:
- Always work upwind and above the manure storage area.
- Keep adults, children and animals away from low-lying zones (e.g. floors) where gas can accumulate.
- Look for affected livestock before entering a barn.
- Design storage(s) layout to minimize exposure risk, considering wind direction and topography.
- Avoid gypsum bedding, especially in barns with confined or underfloor manure storage.
Gas Detection and Safety Equipment
Gas detection monitors combined with safety signage can save lives. Units are available to monitor the concentration of hydrogen sulphide, methane, ammonia, carbon dioxide and nitrogen dioxide. Many monitors are small, wearable, waterproof, and have alarms (sound, light, vibration). Table 2 shows maximum safe gas concentrations or threshold values for exposure during a typical work week.
Table 2 Threshold limit values (time weighted average) for maximum gas concentrations in humans
| Gas | Threshold Limit Value |
| Hydrogen Sulphide (H2S) | 10 ppm |
| Ammonia (NH3) | 25 ppm |
| Methane (CH4) | 1,000 ppm |
| Carbon Monoxide (CO) | 25 ppm |
| Carbon Dioxide (CO2) | 5,000 ppm |
| Nitrogen Dioxide (NO2) | 3 ppm |
| Source: ASABE Manure Storage Safety EP470.1 Standard, OCT2011 (R2016). | |
Farm safety is critical. Busy schedules often lead to shortcuts, but the consequences of ignoring gas risks can be fatal. It is important to know the dangers and use precautions, especially when entering confined spaces. If someone collapses due to toxic gas exposure, do not enter the area – call 911 immediately. Tragically, multiple fatalities often occur when others rush in to help without proper protection.
More information and resources are available from Workplace Safety & Prevention Services (WSPS) and Canadian Agricultural Safety Association (CASA)
OMAFA Weather Summary: Thurs Sept 4—Wed Sept 10 2025
| Location | Highest Temp (°C) | Lowest Temp (°C) | Rain for Week (mm) | Rain Since April 1st (mm) | GDD0C April 1st | GDD5C April 1st | CHU May 1st |
| HARROW | |||||||
| 2025 | 24.5 | 6.7 | 11.7 | 400.7 | 2835 | 2043 | 3069 |
| 2024 | 27.2 | 6.5 | 3.5 | 452.5 | 3001 | 2184 | 3274 |
| 2023 | 30.8 | 11.9 | 10.4 | 580.2 | 2758 | 1959 | 3005 |
| 10 YR Norm (2011-2020) | 26.3 | 13.3 | 20.7 | 495.6 | 2869 | 2056 | 3252 |
| RIDGETOWN | |||||||
| 2025 | 24.7 | 5.2 | 10.0 | 330.4 | 2691 | 1901 | 2863 |
| 2024 | 26.8 | 3.6 | 7.7 | 551.6 | 2837 | 2024 | 3067 |
| 2023 | 30.0 | 11.8 | 4.6 | 504.3 | 2629 | 1839 | 2815 |
| 10 YR Norm (2011-2020) | 25.6 | 11.6 | 24.6 | 452.4 | 2704 | 1896 | 3030 |
| SARNIA | |||||||
| 2025 | 24.1 | 6.5 | 9.3 | 485.0 | 2663 | 1879 | 2812 |
| 2024 | 28.5 | 6.2 | 1.7 | 465.9 | 2847 | 2038 | 3071 |
| 2023 | 31.8 | 13.2 | 28.4 | 450.8 | 2599 | 1810 | 2757 |
| 10 YR Norm (2011-2020) | 26.0 | 12.5 | 20.5 | 452.6 | 2683 | 1877 | 3024 |
| LONDON | |||||||
| 2025 | 26.3 | 5.0 | 10.1 | 338.1 | 2598 | 1835 | 2804 |
| 2024 | 26.0 | 7.0 | 9.4 | 554.9 | 2811 | 1996 | 3054 |
| 2023 | 30.6 | 13.7 | 1.3 | 544.6 | 2608 | 1818 | 2799 |
| 10 YR Norm (2011-2020) | 25.1 | 11.4 | 28.4 | 471.1 | 2677 | 1874 | 3006 |
| BRANTFORD | |||||||
| 2025 | 25.6 | 4.1 | 21.0 | 370.2 | 2641 | 1864 | 2772 |
| 2024 | 27.3 | 6.5 | 2.2 | 460.2 | 2758 | 1947 | 2988 |
| 2023 | 31.3 | 13.7 | 4.2 | 445.0 | 2590 | 1799 | 2770 |
| 10 YR Norm (2011-2020) | 25.6 | 11.0 | 22.5 | 409.8 | 2674 | 1874 | 2968 |
| WELLAND | |||||||
| 2025 | 24.3 | 4.7 | 15.0 | 313.6 | 2697 | 1911 | 2885 |
| 2024 | 25.7 | 8.2 | 13.6 | 472.6 | 2829 | 2014 | 3097 |
| 2023 | 31.9 | 15.1 | 16.9 | 505.4 | 2648 | 1851 | 2856 |
| 10 YR Norm (2011-2020) | 26.2 | 12.1 | 23.3 | 413.9 | 2698 | 1893 | 3036 |
| GODERICH | |||||||
| 2025 | 22.0 | 6.2 | 13.0 | 300.9 | 2501 | 1726 | 2677 |
| 2024 | 27.8 | 6.8 | 39.2 | 369.8 | 2601 | 1797 | 2819 |
| 2023 | 31.0 | 11.5 | 6.8 | 364.1 | 2424 | 1651 | 2586 |
| 10 YR Norm (2011-2020) | 24.1 | 11.1 | 33.1 | 417.4 | 2465 | 1670 | 2782 |
| ELORA | |||||||
| 2025 | 23.1 | 1.7 | 8.0 | 385.0 | 2432 | 1665 | 2576 |
| 2024 | 25.8 | 4.7 | 0.7 | 424.2 | 2550 | 1748 | 2756 |
| 2023 | 31.4 | 11.7 | 8.0 | 444.2 | 2402 | 1628 | 2547 |
| 10 YR Norm (2011-2020) | 23.9 | 9.3 | 31.4 | 466.9 | 2422 | 1631 | 2691 |
| MOUNT FOREST | |||||||
| 2025 | 23.0 | 5.6 | 21.0 | 372.3 | 2443 | 1680 | 2597 |
| 2024 | 26.5 | 5.3 | 6.4 | 401.4 | 2541 | 1744 | 2757 |
| 2023 | 30.5 | 10.9 | 13.4 | 405.4 | 2396 | 1627 | 2550 |
| 10 YR Norm (2011-2020) | 23.7 | 9.5 | 33.0 | 481.4 | 2409 | 1626 | 2708 |
| BARRIE | |||||||
| 2025 | 22.7 | 3.4 | 12.9 | 313.0 | 2448 | 1682 | 2598 |
| 2024 | 25.1 | 4.8 | 24.0 | 558.8 | 2508 | 1710 | 2727 |
| 2023 | 31.1 | 11.4 | 1.8 | 497.2 | 2405 | 1630 | 2569 |
| 10 YR Norm (2011-2020) | 23.8 | 8.5 | 30.2 | 423.3 | 2382 | 1603 | 2662 |
| PETERBOROUGH | |||||||
| 2025 | 24.5 | 1.9 | 23.0 | 337.8 | 2482 | 1706 | 2595 |
| 2024 | 23.6 | 2.9 | 36.2 | 445.8 | 2544 | 1741 | 2714 |
| 2023 | 31.4 | 10.8 | 0.8 | 410.8 | 2464 | 1677 | 2577 |
| 10 YR Norm (2011-2020) | 24.9 | 7.0 | 21.7 | 413.4 | 2454 | 1663 | 2687 |
| KEMPTVILLE | |||||||
| 2025 | 28.2 | 4.3 | 13.1 | 288.5 | 2627 | 1847 | 2783 |
| 2024 | 25.4 | 4.4 | 18.5 | 552.6 | 2697 | 1894 | 2943 |
| 2023 | 32.5 | 10.9 | 3.4 | 509.5 | 2614 | 1832 | 2775 |
| 10 YR Norm (2011-2020) | 24.8 | 8.7 | 22.3 | 459.7 | 2577 | 1787 | 2871 |
| SUDBURY | |||||||
| 2025 | 22.7 | 1.6 | 7.3 | 365.8 | 2198 | 1465 | 2379 |
| 2024 | 26.1 | 3.4 | 15.9 | 500.2 | 2369 | 1596 | 2581 |
| 2023 | 30.9 | 6.1 | 4.4 | 515.0 | 2263 | 1530 | 2429 |
| 10 YR Norm (2011-2020) | 22.6 | 7.3 | 18.8 | 444.5 | 2252 | 1522 | 2561 |
| EARLTON | |||||||
| 2025 | 18.4 | 4.9 | 7.0 | 381.2 | 2141 | 1424 | 2316 |
| 2024 | 26.3 | 1.6 | 40.3 | 484.3 | 2322 | 1556 | 2499 |
| 2023 | 31.8 | 3.5 | 48.9 | 386.9 | 2226 | 1491 | 2365 |
| 10 YR Norm (2011-2020) | 21.3 | 6.2 | 22.8 | 412.7 | 2102 | 1395 | 2374 |
| SAULT STE MARIE | |||||||
| 2025 | 19.8 | 3.7 | 20.2 | 422.8 | 2166 | 1424 | 2309 |
| 2024 | 22.6 | 5.3 | 14.9 | 521.8 | 2227 | 1440 | 2380 |
| 2023 | 31.7 | 3.7 | 7.1 | 391.7 | 2200 | 1464 | 2333 |
| 10 YR Norm (2011-2020) | 21.2 | 7.4 | 40.6 | 465.1 | 2065 | 1337 | 2279 |
| THUNDER BAY | |||||||
| 2025 | 20.4 | 4.3 | 19.5 | 410.0 | 2025 | 1312 | 2212 |
| 2024 | 25.3 | -1.8 | 5.1 | 341.1 | 2137 | 1373 | 2257 |
| 2023 | 31.4 | 3.0 | 29.4 | 300.1 | 2076 | 1364 | 2241 |
| 10 YR Norm (2011-2020) | 21.7 | 4.8 | 16.8 | 404.4 | 2018 | 1299 | 2227 |
| FORT FRANCES | |||||||
| 2025 | 25.6 | -1.9 | 6.0 | 371.2 | 2202 | 1454 | 2386 |
| 2024 | 28.0 | -0.6 | 5.6 | 429.0 | 2218 | 1444 | 2385 |
| 2023 | 28.5 | 2.0 | 3.8 | 311.3 | 2242 | 1523 | 2449 |
| 10 YR Norm (2011-2020) | 22.2 | 5.4 | 15.2 | 406.3 | 2144 | 1408 | 2379 |
This weather summary is compiled by OMAFA using Environment Canada weather station data provided by Agriculture and Agri-Food Canada. Data quality is verified but accuracy is not guaranteed and should be used for general information purposes only. For additional locations and weather analysis, visit the OMAFA Pest and Weather System (PAWS)