Out with the Old, In with the New: Confined Space Ventilation Considerations by Captain Steve Crandall Salt Lake City Fire Department Heavy Rescue Team Coordinator Lead Instructor, Petzl Technical Institute
space response is to ventilate the space. The purpose of ventilation during a confined space rescue operation is to supply enough clean air into the space and/or exhaust enough contaminated air from the space to eliminate any atmospheric hazards present. The ultimate goal of ventilation is to bring the space back into acceptable entry conditions by exchanging the air within the space as many times as possible. Rescuers should consider the following when determining the ventilation method needed during a confined space rescue:
Research indicates that hazardous atmospheres are responsible for the majority of confined space deaths and injuries. OSHA defines a hazardous atmosphere as “an atmosphere that may expose employees to the risk of death, incapacitation, impairment of ability to self-rescue, injury, or acute illness from one or more of the following causes: 1. Flammable gas, vapor, or mist in excess of 10 percent of its lower flammable limit (LFL); 2. Airborne combustible dust at a concentration that meets or exceeds its LFL; . . . 3. Atmospheric oxygen concentration below 19.5 percent or above 23.5 percent; 4. Atmospheric concentration of any substance for which a dose or a permissible exposure limit is published in Subpart G, Occupational Health and Environmental Control, or in Subpart Z, Toxic and Hazardous Substances, and which could result in employee exposure in excess of its dose or permissible exposure limit; 5. Any other atmospheric condition that is immediately dangerous to life or health” (OSHA Standard 1910.146). Most often, these hazardous atmospheres are a result of inadequate ventilation. Consequently, one of the first hazard control objectives for rescuers during a confined 20 | UFRA Straight Tip
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Characteristics and size of the space Size and position of available openings Source and properties of the contaminant Ventilation type and fan capabilities Exhaust location and direction Environmental conditions Equipment and time available Patient condition and location
Mechanical ventilation using fans and ductwork is the only acceptable type of ventilation for confined space rescue operations; passive ventilation is just too slow and ineffective during emergency operations. Mechanical ventilation methods can be divided into three broad categories: positive pressure ventilation, negative pressure ventilation, and combination ventilation. Air exchanges, fans, and ductwork are other factors to consider when ventilating confined spaces. Positive Pressure Ventilation (PPV), also known as supply ventilation, works by forcing clean air into the space through an opening. This introduction of clean air into the space not only raises the oxygen levels back within the acceptable range; it also mixes clean air with any contaminates, diluting them. While PPV does not necessarily “force” products out of the space, it does create a slight increase in air pressure and volume within the space, causing the contaminated air to exit the space out of any available opening. PPV is the quickest, most effective way to change the atmosphere within almost any space. However, rescuers must remember that PPV may cause other potentially undesirable issues as well, such as moving a rich explosive