Ammonia Leakage From Refrigeration Plant

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Ammonia Leakage from

Refrigeration Plant and theManagement PracticeR.K. Gangopadhyay and S.K. DasChemical Engineering Department, University of Calcutta, Kolkata 700 009, India; [email protected] (for correspondence)

Published online 13 July 2007 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/prs.10208

This article deals with the two incidents of ammo-nia leakage in industries situated in West Bengal,

India, and the probable causes of the accident andthe ensuing sequence of events. Emergency proce-dures are also discussed. 2007 American Instituteof Chemical Engineers Process Saf Prog 27: 1520,2008

Keywords: ammonia; leakage; oil separator; hazard;emergency procedures

INTRODUCTIONAmmonia is a chemically reactive gas that is verysoluble in water and is much lighter than air (vapordensity 0.59 of that of air). Cold vapor (e.g., fromleaks) may however be denser than air. Althoughthere have been incidents of exposure to harmfulconcentrations of ammonia in the world there havebeen few fatal accidents. Ammonia is characterizedby a typical pungent odor and is detectable by mostpeople at levels of about 5 ppm in the atmosphere.

Although workers become tolerant to this effect andin the past have been able to work without distressat levels up to 70 ppm, currently the recommendedexposure limit for ammonia is 25 ppm, 8 h time-

weighted average (TWA) and the short-term exposurelimit is 35 ppm, 10 min TWA. At 400 ppm, most peo-ple experience immediate nose and throat irritation,but suffer no permanent ill effects after 3060 min ex-posure. A level of 700 ppm causes immediate irrita-tion to the eyes, and a level of 1,700 ppm (0.17%)

will give rise to repeated coughing and can be fatalafter about 30 min exposure. Exposure to concentra-tions exceeding 5,000 ppm (0.5%) for quite shortperiods can result in death. Response to the effects of

ammonia varies widely between individuals, and thedose-response effects described above are likely tobe those experienced by the more susceptible mem-bers of the population. Henderson and Haggard [1]tabulated (Table1) the physiological response of am-monia.

Ammonia is absorbed in the human body by inha-lation, ingestion, and probably percutaneously at con-centrations high enough to cause skin injury. Dataare not available on absorption of low concentrationsthrough the skin. Once absorbed, ammonia is con-

verted to an ammonium ion as the hydroxide and assalts, especially as carbonates. The ammonium saltsare rapidly converted to urea, thus maintaining anisotonic system. Ammonia is also formed and con-sumed endogenously by the metabolism and synthe-sis of amino acids. Excretion is primarily by way ofthe kidneys, but an insignificant amount is passedthrough the sweat glands. The National Institute forOccupational Safety and Health (NIOSH) recom-mended time-weighted average (TWA) for anhydrousammonia is 25 ppm (18 mg/m3) and the short-termexposure limit (STEL) is the same [2].

PROCESS

Ammonia is used as a refrigerant because of itsparticular thermodynamic properties, which enablesit to move heat far more efficiently than other refrig-erant gases such as halogenated hydrocarbons. It isparticularly suited in the range of 0 to 2308C andhence is widely used for food preservation, the chill-ing of liquids, such as milk, beer and soft drinks, andin the chemical industry. New systems continue to beinstalled. A simple system theoretically needs fourcomponents (Figure 1) (1) evaporator, (2) compres-sor, (3) condenser, and (4) reducing valve. In practiceother components such as an oil separator, inter-cooler, liquid receiver, surge drum, and liquid pumps 2007 American Institute of Chemical Engineers

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are often found. The useful refrigeration is producedat the evaporator. Liquid ammonia at low pressure,and hence low temperature, takes in heat by vaporiz-ing. This vapor is removed by the compressor, which,in compressing it, raises the temperature from belowto above ambient. The hot compressed gas gives upthe heat by condensing to a liquid in the condenser.The high-pressure liquid then passes through thepressure-reducing valve to the evaporator. At the

valve the liquid is cooled as some vapor flashes off.The remaining liquid is available for use in the evapo-rator. In a practical system it is likely there will beother items. An oil separator removes suspended oilcarried over from the compressor and either returns it

to the (pressurized) crankcase or holds it for drainingin some way. There may be a multistage compressor

with an intercooler. Bleeding high-pressure liquidinto the low-pressure side cools this. Downstream ofthe condenser is generally a liquid receiver. Down-stream of the reducing valve a surge drum is oftenfound, which acts as a reservoir of cold liquid andevens out demand on the compressor and condenser.The liquid ammonia is drawn from the surge drumby a pump. Oil drains may be found on surge drums,liquid receivers, and elsewhere on large plants. Thereis also likely to be an automatic control system on allbut the oldest and smallest plants.

INCIDENT 1

Rupture of Manifold During Transfer ofAmmonia from Cylinder to Receiver

Figure 2 shows the detail connection of the cylin-der to the main line. From the ammonia cylinder (65kg capacity) the ammonia is charged into the liquidline connected to the reducing valve, i.e., in the suc-tion side of the ammonia compressor of an ice andcold storage plant. The aforementioned connection

was made by a flexible rubber hose coupled by fix-ing nipples. The rubber hose burst and the ammonialeaked out. This operation was carried out on thenight shift. The plant was located in a thickly popu-lated area of Kolkata, West Bengal, India. Investiga-tion of the incident found that the operator by mis-take opened the valve (V1) attached to the ammoniareceiver instead of opening the valve (V3) attached tothe suction line of the ammonia compressor. The re-ceiver pressure was about 1518 kg/cm2, whereas thetest pressure of the bursting manifold was 12 kg/cm2.So the manifold could not withstand the over pres-sure and bursted. As a safeguard for a possiblerelease of ammonia in the compressor room, there

was an exhaust fan arrangement in the compressorroom for sucking ammonia out of the compressorroom and discharged it to the bottom of the coolingtower. However, the outlet to the exhaust fan was, atthe moment of the incident, dismantled for repair.Hence the ammonia at the outlet through the exhaustfan was not absorbed under water and this affectedthe inhabitants of the nearby houses.

The connection between the ammonia cylinder tothe system line was made by a flexible wire braidedrubber hose coupled by fixing nipples. The chargingline (leading to the said liquid line) was provided

with a inch globe valve and a short piece of iron

Table 1. Acute toxicity: physiological response.

ResponseConcentration

(ppm)

Immediate dangerous tolife and health

500

Minimal irritation 5

Moderate irritation 950Definite irritation 125137Cyclic hyperpnea/upper

respiratory irritation, persistent500 (30 min)

Immediate irritation 700Dyspnea, convulsive coughing,

chest pain, pulmonaryedema may be fatal

1,50010,000

Figure 1. Simple flow diagram for ammonia refrigera-tion system.

Figure 2. Schematic representation of the refrigerationsystem. A: ammonia storage tank, B: evaporator, C:compressor, D: oil separator, E: Condenser, F: Ammo-nia cylinder, P: pressure gauge, V1: inch angle

valve, V2: reducing valve, V3: inch globe valves,FW: flexible rubber hose.

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pipe to facilitate the charging operation. The inchangle valve (V1) of the storage tank was open andthe reducer valve (V2) was closed. As soon the

worker opened the inch globe valve to ensure avacuum in the rubber hose, it was observed thatammonia was coming out profusely from the junctionpoint of the short iron pipe and the rubber hose

where a crack of about 2 inch length was developed.

The worker immediately fled away because of thevigorous leakage of ammonia and the leakage contin-ued. It was also reported that immediately after theleakage started, the compressor was stopped. After ashort while an operator approached the spot to closethe globe valve connected to the said liquid line butfailed as he was not provided with any suitable respi-ratory personnel protective equipment like selfbreathing apparatus. Immediately, two fire brigadeengines arrived in the spot and the operator suc-ceeded in closing the valves by using self-containedbreathing apparatus from the fire brigade people. Asammonia is highly soluble in water, the fire brigadepeople sprayed large amounts of water to dissolve

the ammonia. The effect of the leakage lasted forabout 30 min. Nine female workers in an adjacentfactory were affected and all of them were sent to alocal hospital and were released after first aid treat-ment on the same day.

Probable Causes of the AccidentThe probability of the dangerous occurrence of

leakage is as follows:

1. During charging of ammonia from the ammonia cyl-inder to the liquid line, the bottom valve ( inchangle type) of the ammonia receiver (3 ft O.D. and12 ft long) remained open. The pressure inside the

receiver was around 1518 kg/cm2

. As a result,liquid ammonia came out from the receiver to theliquid line because of backpressure, which escapedthrough the crack in the rubber hose. The rubberhose was designed to withstand up to 12 kg/cm2.

2. No self-containing breathing apparatus was pro-vided and maintained in the factory to tackle thecircumstances arising out of such accidental leak-age of ammonia as a result of which the time spanof leakage of ammonia lengthened.

3. There ware no water sprinklers in the compressorroom to avoid any dispersion of ammonia gasfrom the compressor room to the outside.

4. The compressor room was not provided with any

windows. Only three exhaust fans at a height ofabout 15 ft, located at the extreme west wall wereprovided and maintained which were not suffi-cient to ensure adequate ventilation in the roomby circulation of fresh air.

INCIDENT 2

Oil Separator Drain Line ThreadFailureMassive Ammonia Leakage Throughthe Oil Separator in a Cold Storage Unit

In the refrigeration unit, the drain line from the oilseparator (Figure 3) suddenly detached from the oil

separator body (2 ft in diameter and 6 ft in height),

probably because of a thread joint failure, resulting ina massive discharge of ammonia inside and outsidethe factory. Two workers with self-containing breath-ing apparatus entered the accident spot and isolatedthe oil tank. But the ammonia contained in the oildrum was completely drained. The entire plant wasshut down for about 10 min after the start of the inci-dent and a water sprinkler was also started. The sit-uation was controlled partially with the help of the

water sprinkler arrangement.Thirty workers were affected and all were trans-

ferred to a local hospital for treatment and releaseafter first-aid.

Probable Causes of the Accident

1. The incident occurred because of corrosion in thebottom line of the oil drum.

2. Corrosion was severe due to absence of preven-tive maintenance and due to presence of excessivemoisture in the air, and also because of not carry-ing on periodic testing of those pipes, drains, and

valves by any competent person.3. All the pipelines and valves of the cold storage

plant shall be periodically painted or made ofstainless steel, to prevent corrosion effect.

HAZARD AWARENESS AND ITS REDUCTION

Ammonia is liquefied under pressure in refrigera-tion systems. Liquid ammonia released by accidentmay be in the form of an aerosol, i.e., small liquiddroplets along with ammonia gas. It behaves as adense gas even though it is normally lighter than air,i.e., and may travel along the ground instead of im-mediately rising into the air. This behavior mayincrease the potential risk for the exposure of work-ers and the public [3].

Ammonia vapors are not flammable at concentra-tions of less than 16%, but there may be fire and

Figure 3. Schematic diagram of the oil separatordrum.

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explosion hazard at concentrations between 16% and25%. Mixtures involving ammonia contaminated withlubricating oil from the system, however, may have amuch broader explosive range [3]. Fenton et al. [4]studied the influence of oil on the flammability limitsof ammonia and they observed that oil reduced thelower flammability limit to as low as 8% dependingon the type and concentration of oil.

The following steps are recommended by theUnited States Environmental Protection Agency [3]:

1. Establish a training program for the workers toensure that the ammonia refrigeration system isoperated and maintained by knowledgeable per-sonnel.

2. Consider using a spring-loaded ball valve (dead-man valve) in conjunction with the oil drain

valve on all oil out pots (used to collect oil thatleaks through seals) as an emergency stop valve.

3. Develop written safe operating procedures forremoving oil from the oil out pots and also an

in-house checklist procedure.4. Remove refrigeration oil from the refrigerationsystem on a regular basis.

5. Provide barriers to protect refrigeration equipment,i.e., lines, valves, and refrigeration coils, fromimpact in areas where forklifts are used.

6. Develop and maintain a written preventive main-tenance program and schedule based on themanufacturers recommendations for all of the re-frigeration equipment. The preventive mainte-nance program should include : (i) compressors,(ii) pumps, (iii) evaporators, (iv) condensers, (v)control valves, (vi) all electrical safety(s) includ-inghigh pressure cutouts, high temperature cut-

outs, low pressure cutouts, low temperature cut-outs, low oil pressure cutouts, (vii) ammoniadetectors, (viii) emergency response equipment,includingair monitoring equipment, self-con-tained breathing apparatus, and air-purifyingrespirators.

7. Maintain a leak-free ammonia refrigeration sys-tem. Attention must be made to reports of an am-monia odor and all leaks repaired immediately.Leak test all piping, valves, seals, flanges, etc,should be carried out on regular basis (at leastfour to six times in a year). The methods for leaktesting are sulfur sticks, litmus paper, or a porta-ble monitor equipped with flexible probe is to

be prepared for all times.8. Consider installing ammonia detectors in areas

where a substantial leak could occur. Ensure thatthe ammonia detectors are calibrated regularlyagainst a known standard. Check the operationof ammonia sensors and alarms regularly.

9. Test the pressure relief valves on a periodic rou-tine schedule.

10. Ensure that the ammonia refrigeration system isroutinely monitored.

11. Keep an accurate record of the amount of ammo-nia that is purchased for the initial charge to therefrigeration system and the amount that is

replaced. Keep a record of the amount of lubri-cating oil added to the system and removed fromthe system.

12. Ensure that refrigeration system lines and valvesare adequately identified, e.g., by color coding orlabeling by using an in-house system.

13. Periodically inspect all ammonia refrigeration pip-ing for failed insulation/vapor barrier, rust, and

corrosion. Replace all deteriorated refrigerationpiping as needed.

14. Carry out regular inspections of emergencyequipment and keep respirators, including air-purifying and self-contained breathing appara-tus, and other equipment in good shape; ensurethat personnel are trained in proper use of thisequipment.

15. Consider using the compressor room ammoniadetector to control the ventilation fans.

16. Prepare instructions for emergency shutdownprocedure for the case of power failure.

17. Establish written emergency procedures andinstructions on what to do in the event of an am-

monia release.18. Install remotely operated shut-off valves to stop

the equipment or leaks from a distance.

PRECAUTIONS AGAINST TOXIC RISK

Respiratory Protective Equipment

1. Any person entering an area in which ammoniavapor is likely to be present at a significant level(e.g., for rescue or fault-finding purposes) must

wear a self-contained or airline breathing apparatus.2. Suitable full mask respiratory and eye protective

equipment must be worn by every person carryingout engineering maintenance work on any systemwhere there is a risk of release of ammonia.

3. Everyone who is likely to need to use respiratoryprotective equipment must be properly trained inits use and must be fully aware of its limitations.The equipment must be maintained, kept cleanand examined at least once or twice a month.

Appropriate records should be kept.

Evacuation and Emergency ProceduresAn emergency procedure is prepared which

details the precise duties of all staff and the arrange-

ments for evacuation, rescue, first aid, plant isola-tion, etc. Evacuation procedures are to be clearlyset out and regularly practiced. A common methodis to use the fire alarm provided that actuatingpoints are immediately available at working areas.Personnel should be warned not to approach any

vapor clouds.Adequate exits should be maintained from plant

rooms at, all times. Personnel seriously affected by anammonia escape suffer streaming eyes and violentcoughing and rapidly become disorientated. Theytherefore require clear and prior knowledge of thesafe exit route.



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Ventilation

Compressor houses should be provided withadequate and suitable ventilation to meet the follow-ing requirements: Normal ventilation should be provided to pre-

vent build up of toxic concentrations of ammo-nia from leakage, i.e., from seals, glands, etc.

Emergency ventilation provisions should bemade for sufficient mechanical ventilation toprevent flammable ammonia/air mixtures accu-mulating in the event of reasonably foreseeableplant or operational failure (e.g., valve failure).In such circumstances, the aim should be tokeep concentrations below 25% of the lower ex-plosive limit, i.e., 4% ammonia.

Training in Plant Operation and MaintenanceAll personnel involved in the operation and main-

tenance of the plant must be adequately trained. Thetraining should cover not only general principles ofrefrigeration but also specific points related to the

particular plant. This applies as much to maintenancecontractors as to an employers own staff.

ORGANIZATION FOR MEETING UP AN EMERGENCY

In house planning, proper education for the localauthority and communication with the surroundingneighbors is a must for the successfully handling of aplant emergency situation. It is not possible that onlya group of personnel exclusively tackle the emer-gency situation. As such, the emergency team will bedrawn from the following departments:

maintenance, fire, safety and environment,

personnel, security, and medical.

CommunicationThe terminal manager or manager of the plant will

act as the on-site works main controller (WMC). Theshift manager/engineer in charge of the plant will actas the on-site work incident controller (WIC). The

WIC should be very thoroughly familiar with theplant and be readily recognizable at the scene of theincident. On being alerted by the WIC, WMC takescharge of the situation, opening an emergency con-trol room and operating there from. The WMC should

be familiar with the plant and should have the neces-sary authority to make decisions regarding the affect-ing part the plant and the neighborhood.

After the incidence, the incident identifier who firstactivated the emergency alarm shall report to the

WIC on the location of the incident, probable quan-tity of chemical involved, probable extend of dam-age, wind direction and the actions taken at the site,if any. A communication network for the proposed[5] on-site emergency plan is given in Figure 4.

Emergency Control Center[5]The emergency control center (ECC) should be

located in a position of minimum risk and with good

access both to the affected site and the outside roadsystem so that the controllers could be reaching with-out any difficulty. The ECC should contain

sufficient chairs, tables, and stationeries, several telephones for internal and external

communication, the Material Safety Data Sheets of all chemicals

used on site, a computer with its all accessories with internetfacility for communication and data entrypurposes,

radio contact with all sections of the plant, log book, important telephone numbers on the display board, data pertaining to the decision making, emergency lights, canned food materials and beverages, charts for communication network inside the

plant and outside localities, charts for dispersion distances, diagram to assess weather category, and

layout map for escape routes, assembly points,location for personnel protective equipment, siteentrance and road systems, medical centre loca-tion, location of fire extinguishers/materials etc.

Education and TrainingAll personnel involved in the emergency response

process must be trained to ensure a state of readinessfor various situations. Training of all key personnelshould be carried out regularly and also assess themregularly. Specific training programs are required tosuit the requirement of the specialized personnel as,(a) fire, safety, and environmental personnel; (b) per-

sonnel department; (c) medical personnel; and (d)security personnel [6].

Testing of the Plan by RehearsingEmergency plan procedures are to be developed

and distributed to WMC, WIC, fire, safety and envi-ronmental, security, medical and personnel depart-ments, and on-site emergency control room. The planmust be tested using models and necessary modifica-tions incorporated. An actual mock drill should fol-low this exercise. The shortcomings and inadequaciesin the plan must be identified and rectified accord-ingly. The mock drill should adequately address the

on-site emergency plan, communication network andprocedures, and coordination between variousdepartments and their roles. On the basis of themock drills, all suggestions from the various depart-ments/observers/government agencies should beincorporated to prepare an updated version of theon-site emergency plan for both on-site and off-site.

CONCLUSION

This article deals with two accidents that occurredin a cold storage and ice-manufacturing factory dueto failure of a hosepipe and a valve, causing leakageof ammonia gas from the plant. These accidents have

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affected the work and outside environment and

caused health injuries to the adjacent people. Thecauses of the accidents, the remedial measures, andthe how to tackle the emergency situation have beendiscussed.

LITERATURE CITED

1. Y. Henderson and H.W. Haggard, Noxious Gases,Reinhold, New York (1943).

2. National Institute for Occupational Safety andHealth, NIOSH Recommended Standard for Occu-pational Exposure to Ammonia., US Department ofHealth, Education, and Welfare, Rockville, MD,1974.

3. United States Environmental Protection Agency,

Report No. EPA 550-F-01-009 August 2001 [http://yosemite.epa.gov/oswer/CeppoWeb.nsf/vwResourcesByFilename/ammonia.pdf/$File/ammonia.pdf]

4. D. L. Fenton, K. S. Chapman, R. D. Kelley andA. S. Khan, Operating characteristics of a flare/oxi-dizer for the disposal of ammonia from and indus-trial refrigeration facility, ASHRAET Trans., 101463475 (1995).

5. B. V. Ramabrahman, B. Sreenivasulu and M. M.Mallikarjunan, Model on-site emergency plan. Casestudy: toxic gas release from an ammonia storage ter-minal, J. Loss Prev. Preven. Ind., 9(4) 259265 (1996).

6. Web site: http://www.osha.gov/SLTC/ammoniarefrigeration/evaluation.html

Figure 4. Communication network of the proposed on-site emergency plan.


Ammonia Leakage From Refrigeration Plant

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