Hazards during the Repair and Maintenance of Refrigeration Systems on Vessels  
                                       
                             (For Non-Technicians)
                                       
The repair and maintenance of refrigeration systems can present hazards to workers servicing the systems and those working in the general area.  The two predominant classes of hazardous refrigerants used in vessel refrigeration systems are Ammonia and halocarbons (commonly known as Freon[(R)]) that include chloroflourocarbons[(]CFC)s, hydroflourocarbons (HFCs), and hydrochloroflourocarbons (HCFCs), such as Chlorodifluoromethane (R-22) or difluoromonochloromethane (R-134A). 
Worker exposure to these compounds may occur with leaks, or during maintenance and repair activities.  Dependent on which refrigerant is used different precautions should be followed as described below.  
Ammonia:
Ammonia presents a hazard to workers' skin, eyes, nose, and lungs.  Liquid ammonia is a clear fluid that evaporates quickly at room temperature.  As a gas, ammonia is colorless and has an odor that is suffocating, pungent, and penetrating.  It is also much lighter than air.  If ammonia gas escapes from a refrigeration system or a storage container, it tends to collect in high areas or ceilings.
Ammonia is also flammable at concentrations of approximately 15% to 28% in air.  If released in an enclosed space with an ignition source an explosion may occur.  Employers must follow the requirements contained in 29 CFR 1910.119 (Process Safety Management of Highly Hazardous Chemicals) for preventing or minimizing hazards associated with the release of ammonia.  
Fortunately, ammonia has a low odor threshold (20 ppm), which makes it easy to smell in low concentrations.  However, workers that have been exposed to ammonia repeatedly may experience a significant reduction in their ability to detect ammonia by smell.  Exposure to 300 ppm is immediately dangerous to life and health.  If the possibility of exposure above 50 ppm exists, use the appropriate personal protective equipment (PPE). 
                            Common Odor Thresholds
                                     Range
                                    Hazards
                                  2 - 55 ppm
                        Normal range of odor threshold

Note: If the smell of ammonia is detected and/or you experience eye irritation, leave the area immediately and notify the appropriate person.
                                    70 ppm
Tingling or burning in eyes, nose, or throat; can cause watering of eyes, sneezing, and coughing
                                    300 ppm
Severe irritation of eyes, nose, or respiratory tract, which becomes intolerable after a few minutes; difficulty breathing; possible burning in lungs (IDLH level)
                               2,000 ppm or more
                       Can be fatal after a few breathes

Employers must: 
* Develop and implement safe operating procedures for workers to follow based on a detailed hazard analysis (29 CFR 1910.119(f)(1)).  OSHA requires that these procedures are reviewed and certified annually, as well as a hazard analysis conducted at least every five years (29 CFR 1910.119(e) and (f)(3)). 

* Verify that equipment complies with good engineering practices and is operating in a safe manner (29 CFR 1910.119(d)(3)(ii)).  

* Train workers on the safety and health hazards associated with ammonia, emergency operations (including shutdown), and safe work practices applicable to their job tasks (29 CFR 1910.119(g)(1)(i)).

* Check on each worker, working alone, at regular intervals by sight or verbal communication, including at the end of the job assignment or work-shift, whichever occurs first (29 CFR 1915.84).

For additional information on safety when dealing with ammonia see OSHA Ammonia Refrigeration eTool.
 Halocarbons (or Freon[(R)]): 

The U.S. is phasing out the use of certain halocarbons (CFCs and HCFCs), although they will be available for several more years before being fully phased out around year 2030. 
Halocarbons are not easily ignited and do not burn rapidly if ignited, however, are still toxic.  Also, since halocarbons are heavier than air, they will displace air and can cause asphyxiation in a confined space due to displacement of oxygen.  As a liquid, this colorless compound is volatile, giving off vapors with a faint sweet odor.  Overexposure will cause dizziness due to the lack of oxygen, which is a warning of the onset of asphyxiation.  At higher levels and with long periods of exposure, central nervous system depression and cardiac arrhythmia may result.

When performing hot work in the presence of halocarbons, decomposition products such as Hydrochloric Acid (HCI), Hydrofluoric Acid (HF) and carbonyl halides may form.  These compounds can be toxic at very low levels.  All hot work should be secured during any halocarbon refrigerant leak.
There is currently no OSHA Permissible Exposure Limit (PEL) for halocarbons; however, the National Institute for Occupational Safety and Health (NIOSH) has assigned a Recommended Exposure Limit (REL) at 1,000ppm.  Refer to the common thresholds below. 

                            Common Odor Thresholds
                                     Range
                                    Hazards
                                   1,000 ppm
                        Normal range of odor threshold
                              75,000-100,000 ppm
                            Agitation and dizziness
                                  200,000 ppm
                        Drowsiness, or unconsciousness
                                300,000 or more
                       Can be fatal after a few breaths

Safety Tips for Ammonia and Halocarbon Based Systems:
   
* Employers must provide and ensure workers use appropriate protective gear (such as impervious clothing, gloves, splash-proof safety goggles, face shields - eight-inch minimum) to prevent repeated or prolonged skin contact with liquid refrigerant (29 CFR 1915.152(a)).
   
* Wear appropriate respiratory protection determined necessary by the hazard analysis.
   
* In the event that a leak is detected, the appropriately trained personnel need to determine the approximate location and measures necessary to stop the leak. 

   Note: All ignition sources should be secured and ventilation installed to rid the area of refrigerant vapors.  Unprotected personnel should not return until the affected area, especially bilge areas, has been tested and determined safe.

* Verify atmospheric testing, using a detector tube or other appropriate instrument, to ensure no dangerous level of halocarbon is present.  A Marine Chemist may be required if there is hot work.

* When there is no immediate method for determining the concentration of airborne refrigerant, all leaks should be considered hazardous and emergency procedures initiated. 
   
* Use mechanical ventilation to bring concentrations within the Permissible Exposure Limit (PEL)/ Recommended Exposure Limit (REL).  If concentrations are still above an acceptable level, appropriate respiratory protection is necessary. 
   
* Ensure that all refrigerant, including vapor, is removed and the pressure is 0 psi before disassembling a system.
   
* When performing hot work on refrigerant lines, they should be purged with inert gas to reduce combustion and toxicity hazards.  This process may require a Marine Chemist and a Refrigeration Technician.

* When repairs are complete, re-test to determine if the leak was successfully repaired.  If these repairs do not stop the leak, shutdown the unit until the system can be fully repaired.
   
* When refrigerants are stored in compressed gas cylinders, handle them with extreme caution, as there is the potential hazard of frostbite from escaping liquid refrigerant.  If liquid comes into contact with the skin, wash the exposed area immediately with water and treat the skin for frostbite.

