April 8, 2026: Chlorine gas in Canmore
Greetings,
I had the opportunity to attend a webinar yesterday about the preliminary findings from the Canmore Inn & Suites incident investigation. My original newsletter about the "mass casualty incident" is available here.
The webinar was hosted by the attending public health inspector (PHI) from Alberta Health Services (AHS). All of these matters are FOIPable under public disclosure legislation, however - since the investigation is still ongoing - no official findings have been released yet.
In this newsletter, I'm going to stick the facts as I heard and understood them presented; any gaps exist because the information was not provided or my notes from the session are unclear. I will clearly identify my personal speculation at the bottom. Everything else is based on what I heard in the webinar on April 7, 2026.
The facts are that the Canmore Inn & Suites was hosting many families with children for a local hockey tournament the weekend of January 23 - 25, 2026. The pool was busy throughout the weekend, so much so that hotel staff were managing (limit/control) facility access & usage. The hot tub/spa in the corner under the water slide stairs is immaterial to the incident.
On Sunday morning the hotel pool opened a bit later than scheduled at 9:20am. There was already a line of guests waiting to use the aquatic facility. At approximately 12:30pm, 13 children experienced systems such as red eyes, nausea and/or vomiting; 11 went to the local Canmore hospital (550m away) and one child with the pre-existing condition of asthma was transported to Alberta Children's Hospital in Calgary (100km away).
AHS received notification of the incident from the Primary Care Network (i.e. doctor/hospital) who called in the poisoning event. The pool mechanical system had been voluntarily shut down by hotel staff, and that part of the building isolated from guest access (the pool is at the end of a hallway) until AHS PHIs arrived on site on Monday, January 26, 2026.
Facility records show normal operating tasks were completed by an uncertified pool operator on shift (this is legally permissible in Alberta) on Sunday, January 25, 2026 prior to the pool opening to guests. This included backwashing the sand filter plus draining and refilling the pool system to manage high combined chlorine (CC) associated with heavy & consistent bather load in a relatively small basin.
In the course of their investigation, AHS PHIs spoke to the Ecolab representative for the hotel (this is a contract many hotels have for janitorial & pool supplies; the Ecolab automated pool controller comes with service by the regional Ecolab rep) who visited the site on Sunday, January 25 at 2pm. They stated that before draining the pool, there was visible yellow fluid in the probe basket and hair & lint strainer. When the air release on the filter was opened, there was a strong chlorine odor and people evacuated the mechanical room.
I am unclear who witnessed this (Ecolab or AHS), but also: the sodium hypo (chlorine) and acid (hydrochloric) peristaltic (chemical feeding) pumps were found unplugged from their interlocked outlets and plugged into regular electrical outlets to force feed (manually dose) chemicals. If you do not know what electrical interlock is, please take a few minutes to watch this educational video.
It is AHS' speculation that this was done either 1) during the routine backwash process, or 2) based on the high use period over the weekend - see my speculation below to unpack this. The liquid acid & chlorine met inline (within the pipes of the pool's circulation system) to apparently generate toxic chlorine gas.
It is difficult to estimate how much undiluted hydrochloric acid & 12% sodium hypo fed into the system during the manual feed period. Hotel staff estimated "about 2" from the carboy" (chemicals are not decanted from their delivery vessels) while AHS PHIs attempted to calculate this based on the peristaltic pump size (gallons per minute), length of 2" tubing (chemical feeding line), a pH of 4 ~ using Chat GPT. (Details in this area of the webinar were very unclear to me, so I hope there's more information in the final report.)
The presence of airborne chlorine gas in the pool area is in line the children's medical complaints and firefighter personal safety monitoring devices when they arrived on site at 12:30pm in response to 911 calls.
One of the initial public reports was the kids experienced "cyanide poisoning," but there's no pool operations-adjacent chemicals/products that create cyanide. Further investigation into the safety monitoring devices firefighters in Canmore wear (which do react to cyanide) indicate a false positive could (would?) also be triggered by chlorine gas. No details were provided about the threshold or level. You can read about chlorine gas toxicity levels here.
As of April 2026, the Canmore Inn & Suites aquatic facility remains closed due to an ongoing forensic engineering investigation that will direct further remediation. All applicable staff at the hotel have taken Certified Pool Operator (CPO) training - not with me - and the hotel has committed to AHS that there will now always be a certified pool operator on shift, exceeding Alberta regulatory requirements.
The hotel has also installed a more sophisticated Ecolab automated pool controller that does not allow the acid pump to be unplugged (manually bypassed). AHS will levy further operational requirements and a full process to reopen (closure order is here) once more information is available.
Personal speculation: High bather load on a not-very-sophisticated automated controller was causing free available chlorine (FAC) levels to bottom out (be non-compliant) during routine water testing throughout the weekend. The uncertified pool operator chose - or was directed by the certified pool operator they allegedly called for guidance during their shift - to bypass the system to keep up with the chlorine demand.
Alternatively, the uncertified pool operator was also a new or untrained staff member who did not have sufficient guidance to follow the backwash procedure correctly; they did not know or understand the mechanical components of the pool system.
Personal speculation: I have questions why access to the aquatic facility was uncontrolled, i.e. why the Ecolab representative was allowed to visit the site and drain the basin or service the pool mechanical system prior to the AHS PHIs visiting on Monday, January 26, 2026. I appreciate the honest disclosure of their findings, but what other information was lost?
I understand the site was not considered a crime scene; it didn't require a provincial workplace health & safety investigation (no fatality); and the hotel fully complied with AHS PHIs who directed them to keep the pool area closed to guests. However, I wish the conditions of the incident had been more fully preserved.
Personal speculation: I cannot speak to hydraulics, system design or chlorine gas behavior, however - generally speaking - a swimming pool is not designed to have any backflow. It is my opinion that the undiluted chemicals had to be manually feeding for a very long period of time - or at a very high volume or rate - for the chemicals injected in the main circulation line (pipe) downstream from the filter to make it all the way back to the the hair & lint strainer (prior to the pump) and probe chamber.
Takeaway Action Items
1) The interlock video above is a great tool box topic for your next health & safety meeting - aquatic staff or otherwise - and staff inservice. At a bare minimum, please talk about chlorine and acid being incompatible at all times. I'm not personally an advocate for mixing or slurrying any pool chemicals when manually dosing pools because I feel it creates a dangerous precedent for these types of errors - staff haven't necessarily read SDS sheets to know which are incompatible or dangerous when mixed with water.
2) Purchase outlet safety covers - think childproofing your home - for all ancillary outlets in the immediate area of your chemical feeders in the mechanical room. Consider adding "Do not unplug" tags to power cords and labels to interlocked outlets.
3) Revisit backwash procedures. This will be a controversial opinion, but I've never been a fan of unplugging pumps or turning off probes during routine maintenance such as backwashing; it's too fussy (too many steps/details) and people always forget. I supervised staff for over 10 years and people just plain forget what they're doing or get distracted, and this was well before the current smartphone era. Removing equipment (feeding dangerous chemicals) from the interlocked system designed expressly to administer safety is just not a good routine practice in my opinion.
The argument for doing this is "you're going to save the probe" or "protect the controller" but the alternative is people are messing around with critical setpoints they don't understand. I feel the same during breakpoint chlorination or dealing with an accidental fecal release like diarrhea (nuking the pool with chlorine): don't bother unplugging anything during the short duration of the treatment; with some exceptions, the operating system should be fine and the alternative is - in my opinion - more hazardous.
If you have any follow up questions, please hit reply so I can capture them in the audio recording & next week's newsletter.
Lastly, the session I attended yesterday actually covered two chemical poisoning incidents related to swimming pools in Southern Alberta. The first occurred at the largest YMCA in world in August 2025. I'm not going to try explain the cause of that incident because it was the first time I'd heard about it and barely understood the technical explanation (the presenter spoke very fast). The basic facts are that there was a backflow of pool chemical resulting in extremely low pH in drinking water ingested by children in the adjacent day care and customers at the Jamba Juice.
This week is National Public Health Week. I truly respect the public health officials I'm able to work with on a daily basis. They are often overworked and underpaid individuals working in adversarial conditions who truly do care about public health and safety across pools, restaurants, nail salons, mortuaries, etc.
Public health has saved hundreds of millions of lives. Is yours one of them?
Most can't public officials can't receive any gifts whatsoever, so please consider at least sending your local inspector a thank you email or card.
It's a long newsletter this week, so I've only got the cannot-miss news stories - more next week.
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At one municipality where I was hiring a front desk clerk, I asked in the interview if she knew how to swim. After the candidate left, HR asked me why I asked that? I said we need this basic information because she would be expected to frequently walk out onto the pool deck (next to the deep pool) to deliver messages to aquatic staff. If she fell into the pool, we need to know what to do. She was a great clerk, but all the lifeguards were aware that she did not know how to swim
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This is the same property that had a fire last year. Please see this newsletter for more details.
Katie Crysdale
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PS. I took some much-needed, extended time off last week for Easter, so the audio recording of the April 1, 2026 newsletter will be released shortly on our YouTube channel. We're back on track for this week's audio to be released within the next few days.