Code of Practice for the Application of Coating

7/29/2019 Code of Practice for the Application of Coating

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Code of Practice

for the application of

coatings by spraying of

electrostatic powders


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Published by the

Occupational Safety and Health Service

Department of Labour

New Zealand

Code first issued 1975

Code revised 1980

Reformatted 2004


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TABLE OF CONTENTS

1 GENERAL 4

1.1 Introduction 4

1.2 Legislative Requirements 51.3 Spray Booths and Collection Units 5

1.4 Fire and Explosion Hazards 5

1.5 Toxicity Hazard 6

1.6 Electrostatic Powder Coating Guns 6

2 PLANT DESIGN AND OPERATION 7

2.1 Principles of Hazard Reduction in Plant Design 7

2.2 Design of Spray Booth 8

2.3 Design and Operation of Powder Extraction and Collection Systems 82.4 Explosion Prevention Using Single-Factor Method 8

2.5 Explosion Prevention Using Double-Factor Method 9

2.6 Protection of Plant from Effect of Dust Explosions 10

2.7 Ovens 11

2.8 Protection of Operators Health 11

2.9 Cleaning 11

2 10 General 11

3 ELECTRICAL EQUIPMENT 12

3.1 General 12

3.2 Electrical Equipment in the Hazardous Area 12

3.3 Earthing in the Hazardous Area 13

3.4 Electrostatic Powder Coating Guns 13

APPENDIXA Examples of Powder Concentration and Lower

Explosive Limit Calculations 14

APPENDIX B Explosive Characteristics of Plastic Powders(Representative Values) 15

APPENDIX C Examples of Possible Arrangements for Powder

Collection Units 15

APPENDIX D 17


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IVE1. GENERAL

1.1 Introduction

1.1.1 The purpose of this Code is to indicate the potential hazards in electrostatic

powder coating and to specify the means by which these hazards may be

minimised.

1.1.2 The Code is divided into three parts:

(1) A general section;

(2) A section which gives mainly special details for compliance with the

Factories Act 1946 and the Spray Coating Regulations 1962; and

(3) A section which gives mainly special details for compliance with the

Electrical Wiring Regulations 1976.

1.1.3 Electrostatic powder coating is a process whereby particles are charged

electrostatically to a high voltage and then deposited upon the surface of an

earthed object.

Coating with powder by the electrostatic spraying technique is similar in

principle to electrostatic spray coating with paint. The primary difference is the

absence of solvent; paint is sprayed as a suspension in a solvent base, whereas

powders are applied as fine particles in a dry condition.

1.1.4 The absence of solvent in dry powder applications removes the problems of

paint overspray, solvent fumes and odours, and the risk of fire from flammable

liquids. However, it does not eliminate hazards. Fine plastic powders in

suspension in air can give rise to dust explosions, and can be injurious to health

if inhaled in sufficient quantities. Precautions must be taken to reduce these

hazards to an acceptable level. If adequate precautions are adopted at the

outset, costly modifications to equipment will be avoided later.

1.1.5 Powder should only be sprayed in a booth, as for spray painting, but unlike

wet paint overspray, the oversprayed powder can be recovered and re-used.

For powder spraying the booth is backed up by powder collection units, to

which the powder is conveyed in the ventilating air stream via connecting

ducting.

1.1.6 Not all plastic powders are combustible or provide the same hazards from fire

and explosion. The majority of powders used at present in New Zealand are

epoxy resins and these powders have the greatest explosion hazard. Polyester

powders have a similar explosion hazard rating and other powders such as

acrylic and polythene have lower explosibilities.

1.1.7 Although a dust cloud of polyvinyl chloride (PVC) powder is not explosive,

PVC may give rise to toxic fumes during curing in ovens. Polyurethane

powders may also give rise to irritant fumes during curing, hence ovens using

these powders must be ventilated.

1.1.8 As with paint, electrical equipment which sparks or has a hot surface could bea hazard, but it requires a higher energy spark and a higher temperature than

that for a flammable vapour in order to ignite a dust cloud. The electrical


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equipment also requiries a different construction than that for flammable

vapours in order to protect against the risk of a dust explosion or fire.

1.2 Legislative Requirements

1.2.1 For electrostatic powder coating compliance with this Code will be accepted

by the Department of Labour as satisfactory in meeting the requirements ofSection 48A of the Factories Act 1946, which requires all practicable steps

to be taken to eliminate the hazards from explosible dusts.

1.2.2 Regulation 37 of the Spray Coating Regulations 1962 requires spray coating

by electrostatic means to be authorised in writing by the Chief Inspector of

Factories. Compliance with this Code provides the conditions under which the

Chief Inspector will issue authorisation. Any alteration such as the use of a

different electrostatic powder coating gun requires a new approval.

1.2.3 Compliance with this Code will be accepted as meeting Regulations 67 and 94

of the Electrical Wiring Regulations 1976.

1.2.4 Emissions from the powder collector to the outside air must comply with the

Clean Air Act 1972. An efficient cyclone would normally be sufficient to meet

this requirement.

1.3 Spray Booths and Collection Units

1.3.1 Spray booths are normally either cabinet or tunnel booths. Cabinet booths

may either have an opening in the front of the booth and some method of

suspending objects from the roof of the booth or have openings in each end as

well as the front to allow a conveyor to transport objects through the booth.

Tunnel booths are always open at each end and may also have an opening inthe side to allow for the operator, or may be automatic with only a small

opening to convey the feed-line, or may have an operator located inside the

booth.

1.3.2 The powder is collected from the bottom of the booth so that there is little

powder accumulation in the booth.

1.3.3 The collection unit usually consists of an efficient cyclone, or two or more such

cyclones in parallel.

1.3.4 The small amount of powder escaping from the cyclone/cyclones may also be

collected using one of the following methods:

(i) a fabric filter,

(ii) a second cyclone, and

(iii) a wet (water spray) collector.

1.3.5 A fabric filter may also be used for powder collection without a cyclone, but

because of size and other requirements (i.e. explosion venting) this normally

would be much more expensive.

1.4 Fire and Explosion Hazards

1.4.1 Most of the powder used will burn in any concentration and will present a firehazard in all situations.

1.4.2 The particle size of the powders is in the range which produces dust

explosions.


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IVE1.4.3 The concentration of powder in air must be above a minimum value termed the

lower explosive limit (LEL) in order for an explosion to occur. The LEL

value changes with the type of powder in use (see Appendix B), but will be in

the range 20 - 60 g/m3for explosible powders.

1.4.4 There is also a maximum concentration of powder in air above which

explosions will not occur. This figure is of the order of several kilograms per

cubic metre, but is very ill-defined and in practice could not be stated with any

degree of accuracy. It is safer, therefore, to assume that the powder can

explode at all concentrations above the minimum value.

1.4.5 A cloud of powder in air, which is of sufficient concentration, will explode only

if an ignition source is present.

1.4.6 The source of ignition must be of the required energy for it to ignite a dust

cloud. This is referred to as the minimum ignition energyand is normally

expressed in joules or millijoules. Most values fall in the 10 to 40 millijoules

range (see Appendix B).

1.4.7 The source of ignition must be at a certain minimum temperature to ignite adust cloud. This is referred to as the ignition temperature. Typical values for

a dust cloud range from 4000C to 5500C (see Appendix B). It should be

noted that a layer of dust will ignite at considerably lower temperatures than a

dust cloud; the thicker the layer of dust the lower the ignition temperature.

1.4.8 There are a number of possible sources of ignition such as electrical

equipment, cigarettes and matches, unearthed conductors producing static

electricity, naked flames and hot surfaces.

1.4.9 The whole workroom containing the powder spraying and collection

equipment can be at great risk if accumulations of powder are allowed to arise

in this area.

1.5 Toxicity Hazard

1.5.1 Generally powders used in coating operations have a low order of toxicity and

there is little risk to health in handling and using of powders. As with all dusts,

inert or otherwise, inhalation must be avoided (especially for particles of 10

micron diameter or less), and concentrations of powder in the working

environment should not exceed 10mg per cubic metre.

1.5.2 There are no known instances of skin dermatitis resulting from contact with

epoxy powder used in the coating industry.1.5.3 The irritant fumes given off during curing of polythene powders have a TLV

of 5ppm (TWA) and 10ppm (STEL).

1.6 Electrostatic Powder Coating Guns

1.6.1 The electrostatic powder coating guns may be manual or automatic.

1.6.2 The electrostatic powder gun can, in certain cases, produce a spark when

brought into the proximity of an earthed object and the gun design must ensure

a limited spark energy.

1.6.3 The high voltage electrostatic field generated by the spray guns can build up a

charge of static electricity on any nearby object which is not earthed and which

is capable of accumulating a charge. Unearthed conductors, such as metallic


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objects, are the most likely to accumulate charge, although poor conductors,

such as plastics, can also accumulate a charge but not to a level which is

dangerous for combustible dusts.

1.6.4 Because there is no New Zealand authority for testing electrostatic spray guns,

reliance must be placed on overseas specifications.

2. PLANT DESIGN AND OPERATION

2.1 Principles of Hazard Reduction in Plant Design

2.1.1 The fire risk of stored powder can be treated in the same way as for any other

combustible solid.

2.1.2 The risk of injury from suspended powder explosions or flash fires can be

eliminated by using at least one of three techniques:(1) by providing one means of preventing explosions where all possible

causes of failure have been considered and protection provided against

each possible cause of failure (see Section 2.4 single-factor

method);

(2) by providing two means of preventing explosions, where failure of

either of those means would be extremely rare (see Section 2.5

double-factor method); and

(3) by protecting the plant and surroundings from the effects of a dust

explosion (see Section 2.6).

Most plants do not simply use one of these techniques but use different techniques in

different parts of the plant (see Appendix C).

2.1.3 Eliminating all sources of ignition is not suitable as the sole means of protection

for a single-factor method. Controlling the powder concentration below 25%

of LEL is suitable for the single-factor. method. Collecting the powder in a

water spray would also be suitable (if powder collection was not required say

for one-off operations).

2.1.4 The two means of protection for the double-factor method, which can be

provided with extremely rare failure of either means, are:

(a) by keeping the powder concentration below 50% of the LEL; and

(b) by eliminating all sources of ignition.

2.1.5 There are three methods used to protect plant from the effectsof a dust

explosion:

(a) by providing a lightweight door or bursting panel designed to release at

a low pressure,

(b) by constructing the plant or enclosing the plant in a structure so that it

can sustain the full explosion pressure, and

(c) by using an explosion suppression system i.e. using early-sensing

detectors and rapid-acting extinguishers which contain chemical

suppressant.

2.1.6 Accumulations of powder in the workroom must be prevented by good work

methods and regular cleaning.


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IVE2.1.7 Inhalation of powder is avoided by providing sufficient air movement in the

breathing zone of operators. When this is not practical suitable protective

equipment must be provided and worn.

2.2 Design of Spray Booth

2.2.1 The booth shall be of substantial construction and must comply with theconstruction provisions of the Spray Coating Regulations 1962.

2.2.2 Walls, ceilings and floors shall be smooth and without any projections, so that

powder cannot easily collect in the booth and surfaces are easy to clean.

2.2.3 Floors of booths shall be designed to facilitate the movement of powder

towards exhaust points.

2.2.4 The oversprayed powder shall not be collected in the booth, but shall be

removed continuously from the booth and collected in a properly designed

powder collection system.

2.3 Design and Operation of Powder Extraction and Collection Systems

2.3.1 Each spray booth shall be provided with a powder collection system, which

shall continuously and effectively remove oversprayed powder from the booth

whilst spraying is in progress.

2.3.2 Powder collection units shall be designed to prevent any powder escaping into

the workroom. With manual booths an average air velocity of not less than 0.4

m/s through the main opening shall be maintained during spraying, while the

velocity in the breathing zone of the operator must be at least 0.3 m/s. The air

velocity through openings in the ends of a booth must be at least 0.2 m/s. For

completely automatic booths the air velocity must be at least 0.2 m/s throughany openings in a booth.

2.3.3 Air exhausted from collection systems shall be exhausted to the exterior of the

factory at a point not less than 3 metres above ground level, in a manner that

prevents its re-entry into the factory, unless all powder is effectively removed

from the returning air and explosion venting is not necessary in the plant item

which exhausts the air, e.g. a water wash system.

2.3.4 Air velocity through extraction ducting shall be sufficient to prevent settling of

powder in the ducting. There shall also be no sharp change of direction or of

cross-section in the ducting as this could cause powder to settle out at this

point.

2.3.5 In wholly automatic systems the booth shall contain a fire detection device

which will switch off the powder flow, high-voltage supply and ventilation

system in the event of a fire or explosion.

2.4 Explosion Prevention Using Single-Factor Method

2.4.1 The average concentration of powder in the extracted air from the booth shall

not exceed 25% of the LEL for that powder.

2.4.2 Values of LEL for various powders are given in Appendix B. For powders

whose LEL is not known then the value will be taken as 20 g/m . Where more

than one powder is used then the lowest LEL will become the design criteria.


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2.4.3 The average concentration of the coating powder in the booth is determined

from the maximum rate of powder that can be discharged from the guns in

relation to the volume of air extracted by the ventilation system at its lowest

capacity under operating conditions. See Appendix A for sample calculation.

2.4.4 A plate must be affixed to the booth showing the minimum air volume rate (see

Appendix A) and the design (actual) air volume rate. This plate shall conform

to the pattern shown in Figure 1 and be situated in a conspicuous position.

Markings on the plate shall be legible and permanent. If a new or additional

gun is used giving a different maximum powder flow rate, then the plate must

be altered to give the new minimum air flow rate (see also Section 1.2.2.).

2.4.5 Some means must be provided so that, in the event of the air rate falling below

the minimum, the powder supply to the spray gun will be cut off. An air flow

switch or a switch operating on a pressure differential can be used for this

purpose. If an air flow switch is installed, it must be on the clean side.

2.4.6 Although the concentration may be above the explosive limit close to the gun,

any explosion in this region would not be sustained outside and only a minorpuff would result from a source of ignition existing very close to the gun.

2.5 Explosion Prevention Using Double-Factor Method

2.5.1 The average concentration of powder in the extracted air from the booth shall

not exceed 50% of the LEL for that powder.

2.5.2 The criteria and details given in Sections 2.4.2, 2.4.3 and 2.4.4 will also apply

here.

2.5.3 The powder gun must be interlocked with the fan so that the powder gun

cannot be used without the fan also operating.2.5.4 The spray booth shall be constructed of, or lined with, a material which cannot

accumulate significant amounts of static electricity. Non-conductive and

earthed conductive materials are suitable. Painted conductive materials must

be earthed to protect against any damage to the paint film (see also

Section 3.3.1).

2.5.5 The hazardous area for any sources of ignition is the area within 2 m in any

direction of any opening in the spray booth. Only electrical equipment suitable

for Class II Division I hazardous locations will be allowed in the hazardous

area (see Section 3.2).

2.5.6 No naked flames or other source of ignition shall be permitted within thehazardous area. Earthing and other provisions are given in Section 3.3 and

3.4. If it is necessary to perform any welding on any part of the booth or

powder collection system, all traces of powder shall be removed from the

system prior to commencement.

2.5.7 No person shall smoke or be allowed to smoke in the hazardous area. A sign

stating No Smoking within 2 m in clear lettering shall be prominently

displayed on the spray booth.

2.5.8 Preheating of articles before entry to the spray booth shall not exceed 3000C.

2.5.9 Ovens operating within 2 m of the spray booth shall not have elements, orother heating device, situated within 2 m of the booth if the temperature of the

elements or device exceeds 3000C.


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IVE2.5.10 All fans in the collection system shall be situated on the clean side of the

collection units, and shall be of a type where the motor is fitted external to the

ducting. Downstream from the primary dust collector is considered to be on

the clean side.

2.6 Protection of Plant from Effect of Dust Explosions

2.6.1 If explosion suppression is used as the means to protect the plant, then it must

be designed and supplied by a firm with recognised expertise in this area.

2.6.2 If the plant is designed to withstand a pressure of 700 kPa, then no other

means of protection is necessary. Details of the plant design must be provided

when seeking approval. A flame arrestor or fast-acting valve must be installed

in the ducting close to the booth in order to prevent the flame front from any

explosion returning to the booth. The fast-acting valve should be activated by a

pressure or temperature detector located in the powder collector (or for a

suppression system).

2.6.3 If the plant is explosion vented, then either the plant should be located outsidethe building or the relief vent must be ducted to outside the building. The

explosion vents must discharge at least 3 m above the ground or be located in

an unfrequented place.

2.6.4 The explosion venting standard accepted by the Department of Labour is

National Fire Protection Association (N.F.P.A.) Code No. 68,Explosion

Venting Guide 1978.

If the plant is required to withstand pressure above 20 kPa, then details must

be provided, when seeking approval, to confirm that the plant can withstand

the design pressure. Suppliers of the collection system will also need to specify

the explosion venting area, the volume of the collecting vessel, the pressure at

which the vents release, and the length of the explosion relief ducting.

2.6.5 If the length of the explosion relief vent ducting is longer than 2 m, or if it

contains any bends greater than 10, then either the vessel and ducting must be

capable of withstanding a higher pressure than 20 kPa or the cross-section of

the explosion relief vent must be increased. A distance of 6 m is the maximum

allowable length for an explosion relief vent duct when either the cross-section

of the duct must be twice the area of the vent or the vessel must be capable of

withstanding twice the pressure required for that vent area based on N.F.P.A.

Code No. 68. The requirement for distances between 2 m and 6 m is found

by proportion, e.g. for 4 m the area or pressure must be increased by 50%.

2.6.6 If the dust collector has an unobstructed channel between where the powder is

collected and the rest of the collector, then the whole powder collector must

be explosion vented. A flame arrestor or fast-acting valve must also be

installed close to the booth.

2.6.7 If a cyclone uses a rotary valve or an automatically operated double-flap valve

to separate the collecting vessel from the rest of the collector, then only the

collecting vessel needs to be explosion vented or built to withstand 700 kPa.

This criteria also applies to a filter bag unit when it is used in addition to a

cyclone.


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2.7 Ovens

2.7.1 Powder shall not be allowed to escape into an oven from any source.

2.7.2 The temperature in the oven shall be kept below that at which the plastic will

degrade and produce fumes of the products of decomposition (i.e. normally

2400C). To achieve this a temperature controlling device shall be fitted to

control the temperature in the oven. The temperature controller mustincorporate a fail-safe device, e.g. a fusible link.

2.7.3 Ovens used to cure PVC or polyurethane powder must be vented to outside

the factory. At least 10 m of air per kg of polyurethane powder must be

provided in continuous ovens. Ovens used to cure other powders may not

need to be vented outside the factory depending on the size and operation of

the curing process.

2.8 Protection of Operators Health

2.8.1 No operator shall work, or be allowed to work, within a booth in such aposition that oversprayed powder is present in his breathing zone. The use of

respirators or airline helmets is not a substitute for adequate ventilation but an

approved airline helmet may be used in exceptional circumstances with the

written consent of the Chief Inspector of Factories.

2.8.2 A dust respirator of disposable or cartridge type (approved as suitable by the

Department of Health) shall be provided for use when filling feed hoppers, or

when handling powder in such a manner as is likely to raise a dust cloud.

Preferably cartridge type respirators should be issued individually.

2.8.3 For an automatic system entry to the spray booth shall be prohibited during

operation.

2.9 Cleaning

2.9.1 The spray booth, ducting, powder collection units and the surrounding

workroom area shall be effectively cleaned at regular intervals to prevent

accumulations of powder.

2.9.2 Cleaning shall preferably be carried out with an industrial vacuum cleaner, of a

type powered by compressed air or dust-excluding ignition-proof type of

electrical equipment. If the vacuum cleaning is not of this type, then it cannot

go into the hazardous area while spraying is in operation. A centralised vacuumcleaning system utilising a cyclone or bag filter unit is also acceptable provided

it has adequate protection against dust explosions.

2.9.3 Cleaning shall not be carried out by brushing, although sweeping deposits from

the inside of the booth directly into the collection system is permissible

provided the extraction system is kept in operation.

2.9.4 Powder which is not to be recovered for re-use shall be wetted before

disposal.

2.10 General

2.10.1 Operators of electrostatic powder spraying equipment shall be adequately

trained in the use of the equipment and this training shall be the responsibility of

the occupier.


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IVE2.10.2 Operators shall be made aware of the provisions of the Code where they

relate to the operator or to the operation of the booth. Such provisions shall be

made known to the operator by the occupier, before the equipment is used.

2.10.3 No flammable paints or solvents shall be used or kept within 2 metres of the

booth in a container made of conductive material unless they are earthed in

accordance with Section 3.3.2.

2.10.4 It is recommended that the inside surface of the booth, ducting and cyclone be

painted or coated with a nonconductor as then powder will be less likely to

stay on these surfaces. This will both reduce the explosion hazard and increase

the ease with which colour changes can be carried out. Two cyclones in

parallel may be used to make possible more rapid changes in colour.

Fig. 1 Plate to be affixed to spray booth indicating its air extraction capacity

DESIGN AIR VOLUME RATE m3/s

MINIMUM AIR VOLUME RATE m3/s

3. ELECTRICAL EQUIPMENT

3.1 General

3.1.1 All electrical equipment must comply with the Electrical Wiring Regulations

1976. An extract from the Australian SAA Wiring Rules published by SANZ,

MP 6105: 1976Electrical Wiring in Hazardous Locations, is also to be

used for guidance as it is intended to include most of this material in theElectrical Wiring Regulations.

3.1.2 When the average powder concentration in the spray booth be above 25% of

the LEL, then the concentration is sufficient to require designation of a

hazardous area. The area inside the spray booth and within 2 m of any

openings in the spray booth will be inside the hazardous area.

3.1.3 If because of poor housekeeping or other reasons there are considerable

quantities of explosive dust in the work area, this area shall also be designated

a hazardous area.

3.2 Electrical Equipment in the Hazardous Area

3.2.1 All electrical equipment, including portable equipment, used in the hazardous

area shall be installed with one or a combination of the following requirements:

(a) The equipment and circuitry shall be contained in a continuous

dust-excluding ignition-proof enclosure.

(b) The equipment is totally enclosed fan-cooled or totally enclosed

pipe-vented with no pipe opening within the hazardous area.

(c) The equipment has a special design which has been approved by the

above authorities.

3.2.2 The maximum surface temperature of all electrical equipment in the hazardous

area will not exceed 3000 C.


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3.2.3 Light fittings used to illuminate the interior of the booth and any other light

fittings within the hazardous area must comply with Section 3.2.1.

Alternatively, the fittings can be mounted outside the booth and separated from

the interior by dust-tight panels or wired or reinforced glass.

3.2.4 Plugs and plug sockets used in the hazardous area shall be provided with an

interlocking switch so arranged that the plug cannot be inserted or withdrawn

with the switch in the on position and that the switch cannot be in the on

position unless the plug is in the socket. The plug and plug socket shall be so

constructed and installed that powder will not accumulate in the socket.

3.3 Earthing in the Hazardous Area

3.3.1 The booth and powder collection unit if constructed of conductive material

shall be adequately earthed so that the resistance to earth does not exceed

10 ohm and this shall be checked at intervals not exceeding 6 months by a

competent person. A register shall be kept which is open to inspection.

3.3.2 The article being coated and all metallic equipment in and within 2 m of thebooth shall be adequately earthed while spraying is in progress. The resistance

to earth shall not exceed one megohm.

3.3.3 The earthing of articles being coated depends on the effectiveness of the hooks

carrying or holding the articles, and it may be necessary to carry out a regular

cleaning programme for the hooks to scrape or burn off any plastic coating.

Most electrostatic sprayguns will not work effectively once the resistance to

earth is above 50,000 ohms, hence this will indicate when the hooks need

cleaning.

3.3.4 A powder coating system manufactured by one company uses a technique

which overcomes the poor earthing of articles, hence where this system is

installed an earthing control unit must also be installed to prevent high energy

static discharges. At least one of the known suppliers of these earthing control

units has an agent in New Zealand (See Appendix D).

3.3.5 Operators of hand held spray guns shall wear conductive footwear* and shall

not wear gloves of an insulating nature, nor stand on insulating material.

3.3.6 Personnel approaching within 2 m of the booth during operation shall wear

conductive footwear* unless the powder used has a minimum energy which is

guaranteed to be above 25 mJ.

* Footwear which complies with NZS 5808Electrically conducting andantistatic rubber footwearis satisfactory.

3.4 Electrostatic Powder Coating Guns

3.4.1 Electrostatic powder coating guns must be interlocked with the fan in such a

manner that they cannot operate without the fan also operating (see Sections

2.4.5 and 2.5.3).

3.4.2 Electrostatic powder guns must be classified as instrinsically safe by some

recognised overseas authority such as BASEEFA (British Approvals Service

for Electrical Equipment in Flammable Atmospheres).3.4.3 Of the high voltage equipment only spray guns and the cables connected to

them may be sited inside spray booths. The high voltage generators, or any


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motor driven devices, shall be excluded from the interior of booths, except in

the case of approved spray-guns where the high-voltage generator is sealed

into the gun.

3.4.4 The high tension cables leading to guns shall be protected against damage

during operation.

APPENDIX A

Examples of Powder Concentration and Lower Explosive Limit Calculations

Suppose a booth is equipped with two spray guns both capable of a maximum

discharge rate of 5 g/s, then the total maximum discharge rate = 5 + 5 = 10 g/s.

If the air flow rate is 0.8 m3/s then the average powder concentration

= 10 (g/s,) = 12.5 g/m3

0.8 (m3 /s)

Suppose the powder being sprayed is epoxy, then the minimum air volume rate

for 50% of LEL

10 (g/s)

= = 0.38 m3/s

0.5 x 53 (g/m3) (see Appendix B)

and the minimum air volume rate for 25% of LEL

10 (g/s)

= = 0.76 m3/s

0.25 x 53 (g/m3) (see Appendix B)


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APPENDIX B

Explosion Characteristics of Plastic Powders (Representative Values)

(1) Results on a scale 0-100. 100 indicates severest hazard, 0 - no ignition under test conditions

APPENDIX C

Examples of Possible Arrangements for Powder Collection Units

Example A. In this example the booth uses the single-factor method while the cyclone

has both the single-factor method and protection against the effect of an

explosion (see Fig. 2).

Example B. In this example the booth uses the double-factor method while the

cyclone has protection against the effect of an explosion (see Fig. 3).

Example C. This type of cabinet is portable and has protection against the effect of an

explosion (see Fig. 4).

Type of

Powder

Epoxy

Polyester

Polyester

Modified Epoxy

Polyurethane

Polyvinyl

Chloride

Polythylene

Polyvinyl

Acetate

Nylon

Polypropylene

AcrylonitrilePolymer

Lower

Explosive

Limit

(g/m3)

53

40

45

25

Not ignitable

20

35

30

20

25

Minimum

Ignition

Energy

(mJ)

10-40

Not ignitable

10-40

Ignition

Temperature

Cloud of

Powder (00)

540

500

520

510

Not ignitable

410

520

500

420

500

Maximum

Explosion

Pressure

(kPa)

648

675

660

648

Not ignitable

552

517

655

524

620

Explosibility

Index

DSIR (1)

80

80

65

648

Not ignitable

20-66

0-10

50

Explosive

Dust

Class

2

2

2

Not ignitable

1 or 2

1

1

1

1 or 2


16/17

16

ARCH

IVE

Fig. 2 Example A

Fig. 3 Example B

KEY

1. Average concentration below 25%

of LEL (see 2.4.1)

2. Pressure-differential switch installed

(see 2.4.5)

3. Rotary valve installed (see 2.6.7)

4. Vessel built to withstand 700 kPa

(see 2.6.2 and 2.6.7)

5. Air exhausted outside factory (see 2.3.3)

6. No earthing of object required as special

type of gun used (see 3.3.4)

1

2

3

4

5

6

KEY

1. Hazardous area a set distance from

booth opening (see 2.5.5)

2. Average concentration below 50% of

LEL (see 2.5.1)

3. Object in booth earthed (see 3.3.2)

4. Booth constructed of nonconductive

material (see 2.5.4)

5. A flame arrestor or fast-acting valve

installed (see 2.6.6)

6. Powder gun interlocked with fan

(see 2.5.3)

7. Explosion vent installed (see 2.6.3)

8. Air exhausted outside factory (see 2.3.3)

1

2

3

4

56

7

8


17/17

A

RCHIVE

Fig. 4 Example C

APPENDIX D

At the time that this code was printed the following information was available:

Sames Company manufactures a gun which uses a technique which overcomes

poor earthing; and

Gema manufactures an earthing control unit (Nz agents - Gunn-Gollin Limited).

KEY

1. Average concentration below 50% of LEL

2. Electrodes installed - source of

ignition permissible as below LEL

3. Concentration above LEL

4. Explosion vent installed (see 2.6.3) - not

vented outside but has flame arrestor

(special case for portable unit)

5. Object in booth earthed (see 3.3.2)

6. Cabinet constructed of conductivematerial and therefore earthed

(see 2.5.4)

1

2

3

4

5

6

Code of Practice for the Application of Coating

Documents

Transcript of Code of Practice for the Application of Coating