Home Hot Wash THMG150 – Hot Wash: Pool Chlorine

THMG150 – Hot Wash: Pool Chlorine


In this hot wash episode, Mike explores an interesting topic submitted by a loyal listener in the Midwest.

Thank to our sponsors – CBRNE Convergence World 2018, FLIR, and First Line Technology.

Our hazardous materials training manual, National Emergency Response Hazmat Drills: 50 Drills for Use with Hazardous Materials Personnel, is finally available on Amazon!

Complete Show Notes

3:50 Background on the Situation

  • Chlorine smell coming from a mechanical room on the fourth floor of a high-rise building
  • Staff accidentally mixed 10 gallons of sodium hypochlorite (pool chlorine) with 5 gallons of muriatic acid in a 55-gallon drum
  • This created a dangerous reduction oxidation (redox) reaction
    • This reaction produces an intermediate chemical known as hypochlorous acid (HClO)
    • HClO is very unstable and eventually breaks down to form chlorine gas
    • This is the same chlorine gas we’d find in a 1-ton cylinder
  • Keep in mind that the chlorine wasn’t coming out as fast as it would if you’d just opened a cylinder

6:50 Protecting Ourselves from Chlorine

  • Odor threshold (when our nose can pick something up) is .08 ppm
  • The largest amount of chlorine an unprotected worker can be exposed to is 1 ppm
  • Becomes an irritant to our nose and eyes at 15 ppm

7:50 Working On-Scene

  • Mechanical room was on the fourth floor, while the pool was on the fifth floor
  • Entry team used the elevator and Dräger XAM 5600 single gas meters upon entry
  • Went in dressed in full bunker gear and SCBA – used pH paper to determine whether there was a skin irritation hazard
  • Also brought chlorine meters with them because the initial ticket mentioned a chlorine smell
  • Brought a thermal imaging camera (TIC) along, too – we should always have these if we’re dealing with chemical reactions
  • Responders picked up 30 ppm of chlorine when they arrived in the service area outside the mechanical room
  • When they entered the mechanical room, the concentration went to 50 ppm and then peaked the meter
  • At this point, their science officer was interviewing staff and discovered the staff knew they’d accidentally mixed sodium hypochlorite and muriatic acid
  • It was very helpful to have this information as the entry team was doing their recon and scene size-up
  • Temperature in the mechanical room was in the mid- to high-90s, which was significantly higher than the ambient temperature in the rest of the building
  • This indicated an endothermic reaction was taking place – started monitoring this with their TIC
  • Determined they were dealing with around 15 gallons of mixed product total – way above IDLH in such a confined area

19:00 Eliminating the Threat

  • Building didn’t have any kind of ventilation to the outside, so they couldn’t easily ventilate the area without potentially contaminating other parts of the building
  • Also didn’t want to ventilate onto the street in the middle of the city
  • Going out through the lobby would involve using a stairwell or an elevator, both of which were connected to other parts of the building
  • Decided to put the chemicals into the pool – this area was relatively isolated from the rest of the building as far as ventilation was concerned
  • Putting 15,000 gallons of product into a 32,000 gallon pool significantly diluted the chemicals and put a large amount of space between them
  • Goal was to slow down and/or eliminate the reaction altogether
  • Had to bring the drum up to the pool via the stairs – in the process, one of the firefighters had his face mask knocked off, but was unharmed
  • Gas levels in the pool area began to rise, but leveled off around 50 ppm
  • Firefighters set up a fan ventilation system to push air from the pool area to the hallway to the recreation room and out onto the balcony
  • Took approximately 3 hours from that point before the entire pool area was beneath 1 ppm – didn’t permit re-occupancy of the area until it was at or below .5 ppm
  • Pool company was responsible for dealing with pool levels that were now out of whack – they probably drained and refilled the pool

27:00 Takeaways and Wrap-Up

  • Major communication problems between the command posts and entry team due to concrete walls – overcame this by using cell phones instead of radios
  • Once they got back to the station, the listener’s team got together and talked about what they did well and what they could have done better

Have a question? Send an email to feedback@thehazmatguys.com or leave a message on our Haz Mat Guys comment hotline: 843-628-1484

Show Sponsors
Related Episodes

The Hazmat Guys

Author: The Hazmat Guys


  1. After listening the episode #150 the only thing I would change is to remove the bulk liquids from the container and transfer in multiple 5 gallon buckets or even in brand new gas tanks , the crew had some challenge moving the entire container with the chemical in the stairs creating a potential for firefighter injury , using the method of removing the liquid into a small container will reduce the risk of injury, I would also monitor multiple floors above the incident.


Please enter your comment!
Please enter your name here

This site uses Akismet to reduce spam. Learn how your comment data is processed.