Two farm workers, named locally as Richard Pooley, 36, and Alexander Forman, 32, lost their lives after they were overcome by fumes in a slurry pit at Sunk Island, East Yorkshire.
The incident is the latest slurry pit horror to rock the farming community after three members of the Spence family died after being overcome by slurry gases at a farm in Northern Ireland in September 2012.
Farm safety and transport adviser at the NFU, Tom Price, urged farmers to be wary of workplace dangers.
He said: “The recent tragic events highlight the need for everyone on farm to be constantly vigilant and aware of the potential risks when working around slurry pits and from slurry gas.
“The NFU, as part of the Farm Safety Partnership, has identified slurry pits and slurry gas as one of the significant risks facing those working in the industry. We are campaigning to raise awareness and adherence to best practice when working around slurry pits to help prevent accidents."
According to the Health and Safety Executive for Northern Ireland (HSE NI), slurry gas is a mixture of gasses including methane, carbon dioxide, ammonia and hydrogen sulphide.
The most dangerous of these is hydrogen sulphide as it is extremely poisonous to people and animals. A high concentration removes your sense of smell, causing difficulty in breathing, often resulting in death from only a few breaths.
The latest figures from the Health and Safety Executive (HSE) show 33 farm workers and four members of the public were killed on Britain’s farms during 2014-15.
Mr Price continued: “For many people Christmas and New Year are holidays. However, many farmers will carry on working and accidents can happen.
“We urge all those working in farming to be aware of the risks faced when working with livestock, machinery, at height and around slurry pits.
“Also at this time of year when weather and light conditions can be poor we urge farmers and their workers to take care when working alone and that others know where they are working and when they will report back.”
In the last five years, 160 farm workers have lost their lives: