By Andy Zipser The Newspaper Guild-CWA   WHEN THE FLU-LIKE symptoms began, Doug Weaver didn't give them much thought. It was March, after all. A time when people get the flu. They soldier on, especially if they're young and strong and fighting fires for a living.    And then, Weaver recalled on a perplexed note,  "I found myself tired at a fire." When a lump grew in his groin, he dismissed it as a swollen gland -- but went to see a doctor anyway.    Three hours later, he was in a hospital. Leukemia. Not the most virulent variety. A "relatively decent" survival rate of 80% -- tight grimace over the word "decent" -- but one requiring an aggressive regimen of chemotherapy. Fighting fires was out of the question. Exertion of any kind was out, not just because of the weakness chemotherapy induces, but because of the high risk of infection caused by its near-destruction of the body's immune system.    Medical insurance pays medical bills -- but who was going to pay to feed, house and clothe his wife and two children? What would substitute for the paycheck he suddenly wouldn' t be earning?   "The next morning," Weaver said, "I called my union rep."     IT'S A DECEPTIVELY DANGEROUS business, this job of fighting fires.  There's the heat, of course. The dangers of floors and ceilings collapsing, of steam burns from too much water in the wrong place at the wrong time,  the dreaded flash-overs that give an attentive firefighter perhaps three seconds to escape the inferno that follows.   But those are the  visible hazards, the gross aspects of a multidimensional assault on the human body that grows more complicated with each passing year. Better living through chemistry has given us homes and workplaces built and furnished with a witch's brew of poisons: benzene, formaldehyde, vinyl chloride, polycyclic aromatic hydrocarbons, acrylonitrile, cyanide, heavy metals. Fire releases these and other toxic compounds-- hydrochloric acid, asbestos, arsenic, carbon monoxide -- into the air as gases and fine particles. Contaminated soot and ash coat helmets, bunker gear and boots, work gloves, tools, fire trucks, hoses.   When a fire is extinguished, its by-products live on. And when firemen return to their firehouses, those by-products hitch a ride with them. They get in hair and onto skin, work their way into lungs and other soft tissue, become absorbed into the body and travel to every internal organ. And fester.    Heart disease and lung disease are widely recognized hazards of the profession, said Joseph King, president of Pittsburgh Professional Fire Fighters Local 1. Less well known is the extent to which firefighters are more susceptible to any number of cancers -- sometimes where they're least expected. Testicular cancer, for example, which afflicts firemen at twice the rate of the general population. Brain cancer, at two to four times the norm. Cancers of the rectum, pancreas, liver, stomach, esophagus, bladder, prostate and kidney have all been found, in numerous studies, to afflict firefighters at a rate roughly 1.5 to four times that of everyone else.   And leukemia. One study, for example, found a risk 2.67 times higher for firefighters  than for police officers, often used as a control group because of occupational similarities.   It's the differences that might  kill you.     THE SIGN-UP SHEET appeared overnight at the Bloomfield Firehouse, as if by spontaneous combustion, then almost as quickly spread to other Pittsburgh fire stations. It helped that during his less than three years with the department  Weaver had worked at four different fire houses, transferring ever closer to his ideal location as opportunity presented itself. A lot of firefighters knew him.    But of greater importance was the fact, simply, that firefighters rely on each other in a way few other occupations require. Department rules allow one firefighter to sub for another for whatever reason -- and the subbing began immediately and continued non-stop, week after week and then month after month. As Weaver endured round after round of chemotherapy, each of which put him in the hospital for a week, a steady stream of volunteers ensured his shift was always covered. And  the pay checks kept coming.   "We have a brotherhood," Weaver simply said . "This is what I'd do, and this is what they're doing for me. Hopefully, it won't last too much longer."   There have been four rounds of chemo to date, with one more to go "and, God willing, that will do it for me."  It's not just the chemo itself that puts Weaver on his back.  The treatments wipe out his immune system, making him vulnerable to infections others wouldn't even notice. "The last time it was a splinter," he said, "and that put me back in the hospital for 20 days." Asked how much time he's spent in a hospital bed since he was diagnosed, Weaver thought briefly, then shrugged. "Months," he replied simply.      THERE ARE LOTS of ways firefighters can be hurt on the job, and in most cases they'll readily qualify for worker's comp or disability and early retirement. Burns, broken limbs, torn rotator cuffs, blown knees -- those are the easy calls.  But the internal stuff, that's something else. All kinds of alternative theories can be given to explain away diseases that may take years to manifest themselves.   Causation is hard enough to prove for ailments of the heart, brains and lungs, despite animal studies and epidemiological surveys. But cancers -- those are the real bitch. Look at the decades-long success of cigarette companies in clouding the clear connection between smoking and lung cancer.    No surprise, then, that states are all over the map regarding the burden of proof required of firefighters seeking worker's comp for heart or lung disease or cancer.  Some have presumptive disability laws that recognize the higher risks faced by firefighters: once a sickened firefighter has a medical opinion linking his or her illness to workplace exposure,  the burden of proof is on the employer (or its insurer) to show otherwise. Others place the burden of proof on the victim: not only must the firefighter have a supporting medical opinion, but he or she must then overcome counterclaims that something other than occupational exposure caused the illness. Smoker? Overweight? Family history of hypertension? Sorry. . . .    Which states provide what level of individual protection may be surprising. States not especially recognized for strong workplace protection -- Alabama, Louisiana, Virginia, for example -- offer across-the board presumptive protection for fire fighters; other, more "progressive"  states that one might assume would do likewise, do not, including New Jersey and the District of Columbia. Many offer a mixed bag. California, for instance, recognizes a presumption of work-related illness for heart disease and cancer, but not lung disease; Colorado, for cancer but not heart or lung disease; Florida, for heart disease but not lung disease or cancer.   Pennsylvania? It's right up there with New Jersey -- and Arkansas, Kentucky, Mississippi and a handful of other states you don't envision as bastions of social concern. Fight fires in one of those states and suffer a heart attack or emphysema or cancer -- and, well, you're on your own.    Or would be, if not for the firefighting brotherhood.     IT'S EASY ENOUGH to chalk up Doug Weaver's experience with brotherhood as idiosyncratic, an isolated bright spot in an otherwise hard business long on testosterone and short on human sensitivity. That would be a mistake.   Ralph Sicuro, Local 1 recording secretary, offers as an example the story of a Worcestershire, Mass., firefighter who was scheduled a couple of years ago for a double-lung transplant in Pittsburgh. A fellow Massachusetts firefighter, worried that his co-worker would be alone in a strange city, called Local 1 to alert its members to the situation and asked if they'd visit and make him welcome. They did him one better. Passing the hat, they raised so many thousands of dollars  they were able to house the ailing firefighter's family at a local hotel for the three months he had to spend in Pittsburgh.   Which leads to the inevitable question: What happens if Weaver's chemotherapy doesn't work? How far and how long will his co-workers be willing to prop him up? "Hopefully, it won't last too much longer," he answered hesitantly, before  Sicuro cut in to say, "That's a question you hope you never have to answer."   When it has to be answered, Sicuro added, the reply is, "As long as it takes."  He knows of a case in Florida, he said, in which a firefighter was diagnosed with amyotrophic lateral sclerosis, a disease of the brain and spinal cord that destroys voluntary muscle movement. There, as in Pittsburgh, other firefighters stepped in to work his shifts -- and continued to do so for five years, until he passed away.     THE BILL THAT could help future Doug Weavers passed the state House of Representatives Aug. 19 by the enormously lopsided vote of 186-3. It was referred, two weeks later, to the Senate labor and industry committee, but  there its future is less certain.    Introduced by Scranton representative Kevin P. Murphy, House Bill 1231 would amend the Workers Compensation Act of 1915 by expanding the definition of "occupational disease" to include cancer for firefighters.  Like so many pieces of social welfare legislation, its genesis lies in a personal connection: Murphy's friend, Bobby Shea, recently died from kidney cancer, a disease he believed he had contracted as a Scranton firefighter.    If the bill passes the Senate -- it died there in the last legislative session -- it will be a start. It still will leave Pennsylvania firefighters without presumptive compensation for heart and lung disease. And it probably won't do Doug Weaver any good, Sicuro concedes, because the amended law would have to be applied retroactively.   But it's something. And until there is something, Pennsylvania's firefighters will continue to do what firefighters everywhere have always done, on the job and off. They watch each other's backs.