Home Podcasts 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.

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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

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