One man went to hospital and several others have reported feeling sick, after being exposed to ozone gas and other potentially unknown chemicals during wildfire cleanup efforts in Fort McMurray.

CBC News has interviewed four workers and obtained accounts from two witnesses — all with firsthand knowledge of indoor cleanup work at four properties.

Each described how both fellow workers and some residents returning to live in the city were exposed to ozone gas and other unknown airborne chemicals from ozone generators, which are a type of industrial air freshener that experts, Health Canada and the U.S. Environmental Protection Agency all say should not be used in homes or occupied spaces.

'NO ozone generators! Health Canada advises consumers against using ozone generators in their homes.' - Health Canada website

"It's like the smell of electricity. That's all you can really describe it as, as weird as that sounds. You could smell it in the halls. And they're saying 'oh that's just the smell of purified air, don't worry about it,'" said Dave Gallop during an interview with CBC News when he first raised concerns about worker safety in the wildfire cleanup one week ago.

Gallop said he worked directly with ozone generators while he was under a temporary contract with a restoration company called ServiceMaster. The other three workers CBC interviewed were hired through online job ads for a company called Fort Mac Cleaning, which ServiceMaster subcontracted to help them do the job. All four workers say they received little training on operating and working in close proximity to the ozone generators, exposing them and others in the buildings to ozone gas and potentially harmful unknown chemicals.

While the owner of Fort Mac Cleaning refused an interview, ServiceMaster has defended its training and protection practices.CBC has devoted a separate webpage to the company's response, which you can read here: Multinational company defends its use of ozone gas after Fort McMurray wildfire.

NEW: scroll to the end of the story to read a manufacturer's warning about ozone machines.

Ozone, coughing and lung damage

Ozone generators intentionally produce the gas ozone, which contains an unstable oxygen molecule that reacts with and breaks down other molecules in air — like smoke. Breaking smoke molecules down into smaller pieces does not get rid of them, but it does make them harder to smell. And that is why the machines have been marketed as a tool to banish odours.

But there are harmful side effects that have led federal regulators across North America and industry experts to warn consumers against their use.

CBC News obtained photos like this of ozone work in progress. The man in this photo is wearing a respirator. (Provided to CBC) Health Canada lists the symptoms of ozone exposure as "coughing, chest discomfort, reduced lung function, shortness of breath and irritation of the eye, nose and throat."

Its website includes a strong warning: "No ozone generators! Health Canada advises consumers against using ozone generators in their homes," and links to a page on the U.S. Environmental Protection Agency (EPA) website.

"Often the vendors of ozone generators make statements and distribute material that lead the public to believe that these devices are always safe and effective in controlling indoor air pollution," that site reads.

"For almost a century, health professionals have refuted these claims (Sawyer, et. al 1913; Salls, 1927; Boeniger, 1995; American Lung Association, 1997; Al-Ahmady, 1997). Some vendors suggest that these devices have been approved by the federal government for use in occupied spaces. To the contrary, NO agency of the federal government has approved these devices for use in occupied spaces."

That page goes on to explain the U.S. government prepared the document because ozone can cause "health problems at high concentrations."

Little training, long days

"Did ozone for three days straight and in the buildings we were sleeping in," said a worker who did not want to be named for fear it would affect his chances for future employment.

CBC News obtained photos like this of ozone work during Fort McMurray wildfire cleanup work at the beginning of June. (Provided to CBC) He estimated he worked with and was exposed to running ozone machines over five days, for a total of 15 to 20 hours. This worker said he was not fitted with, nor told to use a respirator.

"We didn't have any training to use the machines. They pretty much taught us on the job. And yes, other people were in the building."

CBC has learned ozone machines were used at four locations: a block of condos at Franklin Landing (the same building block that was burned in a fire unrelated to the wildfires earlier this month), Parsons Creek Village condos and suites at 242 Powder Drive, a motel called the McMurray Inn and the Ace Inn.

Each worker who saw the machines in use, or said they worked directly with the machines, described a process like this: a worker would place an ozone machine into a condo or hotel suite, turn it on, close and lock the door, tape the door and place a "do not enter" warning sign on it. They would then move down the hall and do the same process in other rooms.

CBC News obtained several photos of workers in ServiceMaster T-Shirts, allegedly cleaning hotel suites in Fort McMurray without protective equipment like masks. (Provided to CBC) Some workers were fitted with special respirators they were told would protect them from the gas. Others say they were not. All four workers CBC interviewed reported being told little about the serious risks of ozone exposure.

They also reported that the machines were used very close to or in the vicinity of building staff members, residents who had moved back in, or fellow workers on the site — who were not wearing masks. Accounts from staff members who worked in property management corroborate these details. In one instance, a property management staff member ordered that the ozone machines be shut down and another method used, because of the bad smell.

'You're good. As long as the doors are closed'

Stephanie Brewis is one of the workers who cleaned in buildings where ozone generators were in operation, without wearing a mask.

"One person I saw wearing those special masks for chemicals. I only seen a couple of people wearing those," she said. "And those were the guys doing carpets and doing ozone. None of us were given those things. We were just given little masks like they give you in the hospital, if we wanted them or not."

She said she first started to worry about her own safety when she started smelling strong gas at Franklin Landing, had asthma attacks and reported it to a supervisor.

"And they were like, 'oh no you're good. As long as the doors are closed.'"

This condo complex at Franklin Landing in Fort McMurray is one of the buildings workers say they were exposed to gas from ozone generators. The building burst into flame on Monday, June 6. Authorities say this fire was unrelated to the wildfire. (Olivia Condon/Fort McMurray Today)

After a few days in that building, she was moved to the McMurray Inn motel, where she saw a co-worker who had been working closely with ozone machines for three days have a seizure.

ServiceMaster confirms one of the company's employees who was working with ozone machines did have a seizure, went to hospital and was discharged later that day. Doctors could not definitively say what caused the seizure.

CBC News has interviewed that man, who was one of the people hired through an ad on Kijiji. The man has asked that his name not be used, and that he not be directly quoted, because he said he did not want to jeopardize a full-time job that ServiceMaster offered him.

We follow all the necessary precautions and guidelines. - ServiceMaster

He said a supervisor from ServiceMaster provided him with a fitted respirator as part of the training to use the machines. He was told how to turn the machine on and off, how to tape up the doors and post warning signs, and was told he could be in the room with one of the machines without wearing his mask, but not for longer than one minute.

He and another worker said they were told it was safe to allow others into a room anywhere from five to 30 minutes after they switched the ozone generator off.

Each of the employees interviewed believe they were exposed to the ozone gas during the first two weeks of June. And each individually reported symptoms like coughing, headaches and difficulty breathing. At least two of them reported coughing up blood.

These symptoms match the symptoms related to exposure to ozone gas, outlined by Health Canada.

Both Gallop and Brewis said they were fired before their contracts were finished. Gallop said he was let go for raising concerns, Brewis said she was fired for asking for time off to visit her ailing mother.

Information gaps

The owner of Fort Mac Cleaning turned down multiple phone and email requests for an interview.

CBC News first contacted ServiceMaster Restore, the company in charge of the job sites, about these allegations on Tuesday, June 14. ServiceMaster Canada referred CBC to spokespeople in its head office in Tennessee, which agreed to an interview after CBC published a different story about worker safety concerns on these sites.

Read that story here: Fort McMurray cleanup workers allege dirty treatment in wildfire zone

"Using those type of machines is just a necessary part of some of the restoration efforts on individual properties," said ServiceMaster spokesperson Alison Bishop.

"I can tell you that we follow all the necessary precautions and guidelines to ensure that not only the workers involved in using those machines, but anybody within a specific building, that their safety is considered. And we follow the precautions necessary to ensure that."

Bishop and a colleague said representatives from their head office in Tennessee phoned supervisors with ServiceMaster in Fort McMurray to confirm the franchises operating there were having daily safety meetings with workers, and that they were following safety guidelines. But they could not provide some basic details, including the certification and experience this specific franchise has for working with ozone machines, the name of the special respirator they provided, or the training workers and supervisors received for using ozone machines at these sites.

In addition, the safety measures they described during the interview — fitting workers with a respirator, taping off rooms while ozone machines were switched on and posting signs on doors warning people not to enter — do not appear to match industry standards.

Read the company's full response here: Multinational company defends its use of ozone gas after Fort McMurray wildfire

Standard respirators cannot completely protect from ozone gas

Michael Pinto is the chairperson of the Environmental Health and Safety council for the Restoration Industry Association, an international organization that represents 1,100 restoration firms worldwide.

CBC News obtained photos like this one of people in ServiceMaster T-shirts, who were allegedly working in Fort McMurray at the beginning of June. In some of the photos, people are not wearing gloves or masks. (Provided to CBC) He is a certified safety professional, a certified mould professional, and has worked as a consultant in the restoration industry for more than 30 years, specializing in indoor contaminants.

"The biggest problem with ozone is that it is an irritant. So it does attack the upper airway: the nose and the upper throat and even down into the trachea," he said. "And by irritating that, it then makes that portion of your respiratory system much more susceptible to allowing other contaminants into the body."

'You shouldn't be using the ozone in occupied areas.' - Michael Pinto

Pinto explained that ozone gas does not just target smoke molecules, but rather bonds and reacts indiscriminately with other molecules in the air, resulting in unknown chemical compounds.

And while a special respirator that has a chemical cartridge specifically tested to safeguard against ozone would help prevent exposure to ozone gas, he said there is no guarantee such a mask would protect someone from those other unknown chemicals.

"That is creating a whole cascade of other airborne contaminants. And I'm not sure if the respirator is rated for those contaminants because we don't really know what those contaminants are," he said.

He added that a respirator, even a fitted one with a special cartridge, still has the potential to be ineffective, unless the user regularly measures the ozone concentration in the air around them to make sure it doesn't exceed the percentage for which the cartridge is designed.

'Not a safe practice'

"That's the other reason why the industry, and me as a professional in the industry that represents it, say the same thing: that you shouldn't be using the ozone in occupied areas," he explained.

"If you have somebody with a chemical respirator, and you're sending it in at night after the crew has left, for the few minutes of potential exposure that would probably be fine. But to have that ozone generator running, in the same space where people are not just occupying but working hard? That means that their respiratory rate is up, their body systems are working harder and they're pulling in more air, and they're pulling in more ozone? That is not a safe practice."

Alberta's provincial Occupational Health and Safety department said it has responded to five complaints regarding the Fort McMurray cleanup, two of them related to Fort Mac Cleaning and Servicemaster.

"Two cases have since been closed. OHS wrote one order regarding an employer's responsibility to designate a person to oversee selecting, providing and maintaining respiratory protective equipment," wrote provincial spokesperson John Archer in an email.

"Three cases are still open, meaning officers are still determining if the employer in each case must take any steps to improve safety at their work sites and comply with OHS laws."

OHS laws require employers to ensure workers are adequately trained to do their jobs, which would include knowledge of potential hazards.

OHS laws do not require employers to file a report if a worker is hospitalized for less than 48 hours.

Industry expert Michael Pinto provided the following document to CBC: a copy of the specific user warning from the manufacturer of a brand of ozone generator called "Total Ozone." Pinto said this warning is "typical for the manufacturers" of ozone machines. CBC has not verified what brand of ozone machine the workers in this story were using.