A 500 gallon ASME propane tank is used to supply an interior space heater at an automobile repair shop. During extremely cold weather, the shop's mechanics park cars needing repair the next day inside the garage before they go home so they will be warm and ready for work the next shift. The garage's interior space heater thermostat is normally set on 70° F.
At 6:30 a.m., the first mechanic arrives at the shop and makes a pot of coffee. About 15 minutes after arrival, the mechanic becomes dizzy and sits down on a chair to rest. He subsequently becomes unconscious and falls to the floor.
At 6:45 a.m., the second mechanic arrives at work, enters the garage, and finds his partner unconscious on the floor. He tries to awaken his partner but gets no response. The second mechanic dials 911 for an ambulance.
At approximately 6:55 a.m. a fire department ambulance arrives on the scene. Two Emergency Medical Technicians (EMTs) enter the garage and find both mechanics unconscious on the floor. The EMTs examine the mechanics and observe that they both have reddish colored skin, a classic symptom of advanced stages of carbon monoxide poisoning.
One EMT begins to feel dizzy, and a decision is made to leave the building immediately and call for additional assistance. The call for assistance brings a Command Officer, an Engine Company, an Advanced Life Support Unit (ALS), and a Rescue Squad to assist the EMTs already on scene. Upon arrival, the EMTs brief the Incident Commander on the possible carbon monoxide atmosphere and the location of the mechanics inside the building.
A 500 gallon ASME horizontal storage tank can be equipped with either a single stage or two-stage regulator system. The regulator(s) are designed to decrease the gas vapor pressure from the variable container pressure to the lower pressure required to safely operate the appliance.
In this scenario the appliance is a interior space heater.Most gas appliances like furnaces require venting systems to properly discharge products of combustion to the exterior of the building. If appliances and venting systems malfunction due to age or poor maintenance, there is a risk that combustion products can vent to the interior spaces of the building.
Carbon monoxide (CO) is a major by-product of incomplete combustion. According to the American Society of Heating, Refrigeration, and Air Conditioning Engineers (Ventilation Standard 62-89), a concentration of no more than 9 parts per million (ppm) of CO is permissible in residential living spaces.
The Incident Commander (IC) assigns the Rescue Squad to enter the building in full protective clothing and self contained breathing apparatus (SCBA) to locate and remove the two mechanics trapped in the garage. One member of the rescue team takes a tri-gas monitoring instrument with him that measures flammability, oxygen deficiency and enrichment, and carbon monoxide.
As the rescue team enters the garage, the tri-gas meter's CO alarm activates. The CO reading is 3,200 parts per million (ppm).
While the rescue team is making entry for an emergency rescue, the IC orders the Engine Company to establish a water supply and deploy a charged handline as a precautionary measure. One person is directed to close the valve on the 500 gallon propane tank to isolate and shut down the fuel supply to the heater.
After the mechanics are removed from the building, paramedics establish an airway and begin administering supplemental oxygen at the highest possible concentration. Both patients are treated for shock and transported to the hospital by ambulance.
Note to EMTs and Paramedics: Carbon monoxide easily binds itself to the hemoglobin molecule. It has an affinity for hemoglobin 200 times that of oxygen. Once bound, receptor sites on the hemoglobin can no longer transport oxygen to the peripheral tissues. The result is hypoxia at the cellular level and, ultimately, metabolic acidosis. Hyperbaric oxygen increases the PaO2, which promotes increased oxygen uptake on parts of the hemoglobin molecule which has not yet been bound by carbon monoxide.
Source: Paramedic Emergency Care, 2nd edition, by Bledsoe, Porter, and Shade, pp. 596-597.
This is a top-perspective view of the incident area. Its purpose is only to get the general idea of the incident and surroundings.
In this section, we present an animated version of the incident.