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Grit Blasting & Water Jet Cleaning
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Sand Blasting – Due to associated health hazards “Sand Blasting” is not permitted and rather wherever essentially required “Grit Blasting” shall be used as a method of surface preparation taking all safety measures for personnel as well as plant protection.

Grit Blasting: Generally not permitted in hazardous areas. The pipe work or process vessel to be grit blasted, should where ever possible be isolated and de pressurized. Grit blasting should be authorized only with a hot work permit with all safety precautions duly taken care of. Grit blasting is not permitted on the following equipment.

a)      Any pressure vessel or pipe line which has not been inspected and approval by inspection and corrosion team.

b)      Any process pipe work containing hydrocarbon or flammable substances previously identified having minimum wall thickness equal to less than 2.0 mm (Category X defect) or and if the calculated Maximum Working Pressure is equal to less than line operating pressure or the protecting relief valve setting (Category D defect).

 

Precautions during Grit blasting:

a)      The permit applicant and permit issuer must ensure that the requirement of grit blasting is fully justified and cannot be delayed until a facility shutdown period.

b)      Before and after commencement of the job, the permit applicant and the permit issuer should assure that positive protection is taken to protect cable runs, gas detection heads, instrumentation and operating equipment in the immediate grit blasting areas, and satisfy themselves that the work is been carried out safely.

c)      Prior to the job and continuous monitoring of gas check to be done by an authorized gas tester before and during the entire work period.

d)      Barricading and warning sign stating “grit blasting in progress” to be displayed and erected around the area of grit blasting.

e)      Only authorized personnel to be allowed inside the cordoned off area. Suitable sheeting must be made available inside the restricted area to protect the personnel being struck by grit material.

f)        All gas cylinders must be removed from the cordoned off area and max protection to be given if the materials cannot be removed.

g)      Any painting works done in near by areas to be seized off prior undertaking the grit blasting operation.

h)      All pipe work/equipment must be adequately bonded to earth to prevent the build up of electrical charges on any process equipment. This requirement applies to the blasting pots, hoses and compressors.

i)        The blast gun must be fitted with a dead man’s handle, which must be checked for correct operation prior to starting grit blasting.

j)        One competent supervisor must be nominated to oversee the grit blasting operation continuously. He must be continuously present during the grit blasting operation and not involved in any other activities. He should know the location of fire fighting equipment and know how to use it. He should know how to shut down grit blasting equipment in case of an emergency situation.

k)      The workers should use suitable PPE against exposure of dust and other health hazards.

l)        The spent grit shall be recovered and safely disposed to approve waste disposal facility.

m)    The following minimum fire fighting equipment must be kept available during the entire operation. Two pressurized water hoses run out and tested. The fire hoses are to be taken from separate hydrant in order to approach from two directions. Two suitably positioned fire extinguishers should be placed. At least one gas detector near grit blasting location and another at compressor site to be provided.

 

High Pressure Water Jetting: this refers to cleaning with water jets at pressure greater than 2000 psi and up to around 20,000 psi. Such equipment is very effective for removal of coatings and scale as well as in metal cutting. Jetting shall be handled by competent persons only taking following minimum precautions.

a)      The worksite shall be cordoned off and warning signs to be placed in safe distance to warn personnel approaching the area.

b)      Minimum number of workers shall be kept during the work and all occupational hazards to be clearly made aware to them.

c)      PPE can be effective against water spray and flying particles, but not to direct impact of the jet itself.

d)      The worker must wear the required PPE such as PVC suit, hand gloves, safety boots, ear muffs, safety goggles or face shield and safety helmet.

e)      The injury caused due to water jetting may damage inner tissues although not seen at surface and must be referred to hospital for treatment.

f)        Equipment, accessories such as hose, couplings and connector shall be suitable for pressure rating of the system and maintained in accordance with manufacturers instructions. The pump shall be equipped with a relief valve or regulator set at 10% above the rated working pressure of the weakest component in the system.

g)      The connector and coupling joining different lengths of hoses must be suitable for sustaining the pressure implied.

h)      If the equipment is assembled from separate components immediately before use, then a pressure test shall be conducted prior to operation at a pressure not exceeding rated working pressure of the weakest component.

i)        A fail safe trigger must be provided on the jetting gun.

 

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