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Hydrogen sulfide H2S). Hydrogen sulfide is a colorless gas with an offensive odor sometimes likened to rotten eggs. It is highly toxic, with an IDLH of 1,200 ppm, flammable, and heavier than air. It has a wide flammable range of 4.3% to 46% in air. It should be noted that gases and vapors with wide flammable ranges are likely to burn inside containers and confined spaces, unlike those with narrow ranges, like gasoline, that would be too rich to burn in a container or confined space.
Hydrogen cyanide (HCN). Hydrogen cyanide, also known as hydrocyanic acid, is a gas that has a faint odor of bitter almonds and a vapor density of 0.938, which makes it lighter than air. It is toxic by inhalation with an IDLH of 50 ppm, and flammable, with a wide flammable range of 6% to 41%. Its flash point is zero degrees Fahrenheit and the autoignition temperature is 1,000F.
Anhydrous ammonia (NH3). Anhydrous ammonia is a colorless gas with a sharp, intensely irritating odor. It is corrosive, toxic and flammable under certain conditions. The IDLH is 300 ppm and it is toxic by inhalation. Ammonia also seeks water in moist parts of the body and can cause chemical burns when it combines with water on the skin. Ammonia has a flammable range of 16% to 25% in air and an autoignition temperature of 1,204F. It is a serious fire hazard inside of buildings and confined spaces.
Chlorine (Cl2). Chlorine is an elemental gas that is toxic and an oxidizer. When in contact with organic materials, it can react explosively. It is toxic by inhalation with an IDLH of 10 ppm. Chlorine is heavier than air.
Hazardous materials other than those usually expected to be found in confined spaces can be spilled during incidents and find their way into confined spaces, especially those in which vapors are heavier than air. Response personnel must be aware of this potential and plan tactics accordingly. Dust can also be a hazard in a confined space that can result in dust explosions, respiratory difficulty, injury and death.
Confined space entry may produce exposure to elevated or reduced temperature conditions resulting in an increase or decrease in body temperature, both to victims and rescuers. Hazmat personnel experience some of the same exposures to heat and cold stress during entry into incident scenes in chemical protective clothing. Rescue personnel should be prepared to deal with heat stress types of injury in addition to any other potential dangers in confined spaces.
The National Fire Protection Association (NFPA) has established training competency levels for emergency personnel responding to emergencies in confined spaces in NFPA 1670 Operations and Training for Technical Rescue Incidents. NFPA has established three levels of operational capabilities for personnel responding to confined space emergencies: awareness, operations and technician.
Awareness level. Awareness personnel do not make entries into confined spaces; they are primarily attendant or support personnel. They must be able to recognize confined space emergencies, make proper notifications, initiate contact with victims if possible, implement emergency response system for confined space emergencies, and implement site control and scene management.
Operations and technician are the levels of training that allow entry into a confined space.
Operations level. Operations personnel are involved in protecting personnel, size-up, identification of the duties of the rescue entrants and backup, monitoring procedures and entry-type rescue procedures and others.
Technician level. Technicians are involved in medical monitoring of rescue team members, planning response for entry-type rescues in hazardous environments and implementation of the planned response and others.
OSHA believes that education on confined spaces and training on proper entry techniques could lead to prevention of 85% of the deaths and injuries resulting from confined space entry operations. This would likely result in the reduction of deaths and injuries among emergency response personnel as well. All emergency response personnel who may respond to a confined space rescue incident should be trained to a minimum of the awareness level for such response, including fire, police, hazmat and EMS.