Home Hot Wash THMG177 – Hot Wash: CO2

THMG177 – Hot Wash: CO2


In this hot wash episode, Bob and Mike discuss a CO2 response and take a long-term look at the incident.

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Complete Show Notes

3:15 The Situation

  • Typical CO2 run in Manhattan – CO2 alarm had been going off in a restaurant
  • Responded within 20 minutes – first two units were already there
  • Mike had the science/research position and Bob was driving the second piece
  • Oxygen levels were good (no SCBA required), and the entire building was clear to walk around in
  • CO2 tank looked normal – manager had shut off the vapor line valve at the advice of the manufacturer
  • Manager reported that when she turned the valve off, there was ice all over the pipes and down the tank
  • When Bob and Mike’s team arrived, however, the ice was completely melted
  • This means everyone at the restaurant had been exposed to CO2 throughout the course of the day

7:50 Why Are These Tanks So Popular?

  • We’re seeing these compressed liquid CO2 tanks all over the place (especially in foodservice) because they’re so convenient
  • Businesses in densely-populated areas are putting these units in basements since they have nowhere else to go with them
  • Units leak in confined, small areas that fill up quickly – poses more of a health risk to people in the vicinity

11:00 CO2 Facts and Figures

  • We measure CO2 in ppm or percentage of volume
  • Alarms typically read in ppm, while our meters typically display percentage of volume – important for us to know the conversion
  • TWA (time-weighted average) is equivalent to the PEL – 5,000 ppm or .5%
  • IDLH (immediately dangerous to life and health) is 30 minutes at 40,000 ppm or 4%
  • STEL (short-term exposure limit) is 15 minutes at 30,000 ppm or 3%
  • EPA only allows for 1,000 ppm or .1% at continuous exposure

14:45 Signs & Symptoms of CO2 Exposure

  • Acute exposure:
    • We usually only see/think about the acute effects of CO2 exposure – slight asphyxiation, dizziness, etc.
    • These symptoms often occur pretty quickly if there’s a significant leak in a cryo tank or very little ventilation
  • Chronic exposure:
    • Easier to detect than acute exposure and generally less catastrophic
    • Slow leaks in gas lines are one of the most common sources of chronic CO2 exposure
    • In this case, the icing on the tank indicated a long, low-flow leak had been transpiring
    • The more generalized frosting on the tank, the longer it had been off-gassing

19:00 Pathophysiology of CO2

  • Start by understanding that unlike many asphyxiant gasses, CO2 is an intricate part of our biological system
  • CO2 is an end product of our metabolism – we breathe when we need to get rid of CO2
  • As we breathe fresh air into our lungs, our cells take in oxygen, use it in the metabolic process, and spit CO2 out into the bloodstream
  • As CO2 mixes with the water in our blood, it creates carbonic acid, which quickly builds up as more cells give off CO2
  • This means our blood becomes more acidic – when these levels reach a critical point, it triggers us to breathe
  • Resulting signs and symptoms would seem to indicate that our first sign an employee was in the mix would be an increase in respiratory rate
  • 1.5-2.5% in the air over a day would give mild respiratory stimulation
  • 3-4% could quadruple the breathing rate in a healthy person
  • At 5-6%, it only takes an hour to see significant respiratory response
  • Symptoms of high or prolonged exposure to CO2 include headache, increased heart rate, dizziness, fatigue, rapid breathing, and visual and hearing dysfunctions

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