Hose  Mask  Respirators.–  These consist of a facepiece,  breathing  tube,  harness,  and  large  diameter, thick wall, nonkinking, air supply hose. The air may be supplied by a blower, either motor or hand driven. Air-Line   Respirators.–   These  consist  of  a facepiece,   hood,   helmet   or   suit,   breathing   tube, regulator,  and  small  diameter  hose  provided  with  some means to attach the hose to the user. Air is provided by a compressor, ambient air breathing apparatus (AABA), or compressed air cylinders. There are three types of air-line respirators. 1. 2. 3. Demand:  Available  only  with  a  facepiece,  it supplies air to the user on demand (when he inhales). Pressure  Demand: Available  only  with  a facepiece, it maintains a continuous positive pressure  within  the  facepiece. Continuous  Flow:  Available  with  facepiece, hood,  helmet,  or  suit,  it  provides  a  continuous positive pressure and flow of air. SELF-CONTAINED BREATHING APPARA- TUSES.– These consist of a facepiece, helmet or hood, a breathing tube, and a source of air or oxygen, all of which are carried by the wearer. SCBAs are divided into the following  closed-  and  open-circuit  types: Closed Circuit.– In closed circuit, or rebreathing, SCBAS,  carbon  dioxide  (CO₂) in the exhaled breath is removed by a chemical canister, and the remaining air is rebreathed. There are two types: In one type the oxygen is provided by either high-pressure gaseous oxygen  or  gaseous  oxygen  converted  from  liquid oxygen. In the other type the water vapor in the exhaled breath reacts with a chemical in the canister to release oxygen. The Navy oxygen breathing apparatus (OBA) is  an  example  of  the  second  type.  The  OBA  is  not approved by NIOSH/MSHA for commercial use, and it is only authorized for damage control and fire-fighting operations aboard ship. OBAs MUST NOT be used in flammable atmospheres because of the heat generated by the canister. Open Circuit.– In this type of SCBA, the exhaled air is expelled to the atmosphere, and air is provided to the user from a compressed air cylinder. This type of respirator   is   available   in   either   a   demand   or pressure-demand   model. Emergency  Escape  Breathing  Device (EEBD).–  This  a  special  type  of  SCBA  developed specifically  for emergency  escape from shipboard fires. It has a short-duration air supply. IT MUST NEVER BE USED  TO  ENTER  A  HAZARDOUS  ATMOSPHERE; IT IS FOR ESCAPE ONLY! SELECTING RESPIRATORS Use  only  respirators  that  are  jointly  approved  by NIOSH/MSHA. If there is any doubt as to the respirator required to protect against a particular contaminant, ask an industrial hygienist. Different  respirators  protect  against  different contaminants  and  concentrations  of  contaminants,  so you must select one that protects you from specific contaminants.  The  industrial  hygiene  surveys  will  give you information on how to match contaminants and respirators. Or if you need new information, ask an industrial  hygienist  for  help.  Before  you  select  a respirator, always ask the following questions about the conditions where you plan to use it: l l l l l l l l What  are  the  warning  properties  of  the contaminant (smell, eye irritation, or respiratory irritation)?  Some  contaminants  do  not  have enough  warning  properties  to  alert  you  to respirator  failure.  Vapor-  and  gas-removing respirators   are   not   approved   for   some contaminants  that  include  carbon  monoxide, hydrogen  cyanide,  isocyanates,  and  methyl alcohol. Is the contaminant absorbed through the skin? Are any of the contaminants IDLH, or will they cause ill effects after prolonged exposure? What  is  the  concentration  of  the  contaminant  in the  atmosphere? What  are  the  NAVOSH  standards  for  maximum levels  of  contamination  in  a  given  environment? Is the atmosphere oxygen deficient or oxygen rich or will such conditions be created? What is the nature, extent, and frequency of the duties to be performed in the work area? What degree of protection is provided by the particular respirator? USING RESPIRATORS Before you may use a respirator, you must meet the following   requirements: .  Be  certified  by  the  MDR  as  medically  qualified to use each type of respirator required. 10-10