A confined space is an enclosure with limited entry and exit. It has the potential for dangerous atmospheric contamination because of poor ventilation, and is not intended for continuous occupancy (e.g., tank, sewer, silo [558-560]). Such a space may require periodic inspection, maintenance, repair, or cleaning (560). A confined space also can have an open top and be of sufficient depth to restrict ventilation (e.g., pit, trench ). The typical scenario is that a worker enters the space, is overcome, and dies. Another worker, who attempts rescue, also collapses (560-562).
Room air typically contains 20.9% O2, 79% nitrogen, and 0.1% CO2, water vapor, and other inert gases (2,499,563). Contamination of the confined space atmosphere includes, but is not restricted to, any combination of O2 depletion (asphyxiating), presence
of explosive, flammable substances (flammable), irritant and corrosive chemicals (irritant and corrosive), and adverse concentrations of toxic substances (toxic [558,559,563]). Features of a confined space atmosphere that are immediately dangerous to life have been defined: an O2 concentration of 16% or less; a minimum flammability level concentration of a combustible gas or vapor that will ignite if an ignition source is present; and a concentration of the toxic substance, immediately dangerous to life (269,559,563-566). Irritant or corrosive substances can affect the respiratory system alone (e.g., ammonia) or have combined respiratory/systemic effects (e.g., benzene ). Lack of O2 is the most common cause of death (560). A level of O2 less than 5 to 10% is incompatible with life resulting in death within minutes (see Chapter 4, Subheading 4.1.). Breathing gas lacking O2 causes unconsciousness in seconds (567). Breathing ceases, but cardiac output can continue for a short time (567). If the fall in respired O2 happens slowly, the victim experiences fatigue and is unable to escape (567).
The lethal level of CO2 is above 10% (2,493,499,562,564,566,568,569). CO2 is 1.5 times heavier than air and can "pocket" (2,269). CO2 not only asphyxiates, but also causes acidosis (2,499). CO2 is fatal even when atmospheric O2 is normal (2,570). An atmospheric concentration of 30% causes unconsciousness in seconds to minutes (568). At high levels, CO2 induces narcosis (568).
Zugibe et al. defined confined space-hypoxia syndrome as a confined space death owing to an oxygen-deficient environment (Fig. 68) (559,564). Decreased atmospheric oxygen can result from consumption by microorganisms, work-related activities (e.g., welding), chemical reactions (e.g., rust), absorption by agents stored in tanks (e.g., activated charcoal), and displacement by another minimally toxic gas (e.g., propane, nitrogen, methane accumulation in a silo or sewer [2,269,558,560,563,564,567,571]). The displacing gas can also be toxic (e.g., CO generation from microbiological breakdown of organic matter, release of hydrogen sulfide during removal of putrefied organic material and industrial waste [558,561,572,573]). Some gases that displace O2 (e.g., propane) have CNS depressant effects at high atmospheric concentrations and lead to cardiac arrest (311). Mechanical hazards (e.g., machinery), adverse thermal conditions (hypothermia, hyperthermia), and falling objects pose additional threats in confined spaces (558,563). Workers trapped in cave-ins can be covered and suffocated (see Subheading 3.8.1. and ref. 574). Cases of children trapped in refrigerators has been described (48,114,116).
Atmospheric testing for noxious gases and O2 levels at the death scene and postmortem analysis of blood and other tissues must be done (269,561,562,564,572,575). Scene simulations may be required (2). Airtight metal containers are used to collect lung tissue (311). CO2 is elevated normally in postmortem blood and cannot be tested.
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