Firefighters have called for more protection amid fears they may be more likely to die from cancer than the rest of the population.
Research shared with the BBC's Inside Out programme implied that they may be more at risk because of exposure to harmful toxins on their clothing and equipment.
Professor Anna Stec, a fire chemistry and toxicity expert at the University of Central Lancashire, said: "In my opinion, there is a direct link between a firefighter's occupation and cancer."
She added that in her view "firefighters are twice as likely to die" in such a way compared to the general population, saying: "They're dying from not one type of cancer, but they've got multiple types."
She said research had indicated that when firefighters start sweating in a hot environment, levels of absorption via the skin increase, creating a sort of "sponge for all the fire toxins".
It is feared that harmful carcinogens are being passed from one place to another through the storing of equipment and because those working in the industry sometimes do not have the time to properly clean their clothing between incidents.
One former London firefighter, Mitch Coplestone, who has two forms of leukaemia and is in need of a bone marrow transplant, told Inside Out: "Firefighters need to stop having their lives turned completely upside down with cancer."
He added: "Cancer in the fire service is indiscriminate. It's young people, old people, middle-aged people and there seems to be an unbelievable amount of firefighters catching cancers.
"It needs to be stopped. It needs to be addressed."
Detailing some of the work being conducted by her team, Prof Stec suggested that the clothing worn by firefighters might explain a potential link to cancer.
She said: "If you take firefighters in their clothing, in a hot environment, they start sweating, they start dehydrating, body temperature increases, and dermal intake or absorption via the skin is automatically increasing. It's kind of working like a sponge for all the fire toxins. So we're looking at the type of clothing.
"We will heat it up, we will see if there are any contaminants within the deeper layers of the clothing, to see what effect and what danger and risk they will bring to firefighters."
A current firefighter, Chris Moore, has non-Hodgkin's lymphoma, and believes he got the cancer as a result of his work.
Mr Moore, who works in South Shields, said: "I'll give you an example - fire gloves get covered in dirt and muck and smoke and soot and toxic and carcinogenic chemicals, and we store them in our helmets. So when we go out to the next incident you take your gloves out of your helmet and you stick the helmet on your head.
"I've done that for 25 years. It's no surprise that I've now got a cancer of my blood system."
Fire officer Chris Davies, who works as the lead for health and safety at the National Fire Chiefs Council, said: "There is a lot of scientific and medical information out there, but all of it, that I'm aware of, states that you can't prove or disprove a link to cancer.
"What I do acknowledge is firefighters are contracting certain types of cancer above the population norm, I accept that and that is a concern."