Controlling static hazards when handling IBCs
October 1st 2008

IBCs provide many storage and transportation

advantages. Their capacity to store larger volumes

than standard barrels and the effort required to fill,

transport and store larger quantities in the same floor

space support more time efficient and cost effective

supply chain operations explains Newson Gale

The compatibility of materials with IBCs and their method

of storage and handling are of particular interest to health

and safety regulators. In 2008 the UK's Health & Safety

Executive, in collaboration with the Chemical Business

Association (CBA) and Solvent Industry Association (SIA),

issued general guidance outlining the type of assessments

that should be carried out to manage the risks associated

with IBCs storing flammable and combustible material.

Of particular interest is the assessment for managing

the risk of electrostatic ignitions. The HSE refers to the

SIA's notice No.51a which provides guidance on

minimising the risk of incendive electrostatic spark

discharges when storing solvents in IBCs.

Electrostatic hazards and IBCs

The risk of electrostatic discharges in potentially

flammable or combustible atmospheres is well documented

in best practice standards like Cenelec's CLC/TR:50404 and

NFPA 77. Although identifying static as a hazard is

difficult to visualise, as it is not readily tangible or easily

detectable, the underlying theory and safe practices that

can be put into place are relatively straightforward.

The flow of any material in pipes, filters and fittings,

whether the material is conductive or non-conductive,

results in the separation of charges. The separation of 1

electron in half a million is all that is required to provide

the right conditions for an incendive spark discharge to

occur. Much the same way a spark plug works in the

engine of a car, electrostatic discharges result from the

existence of a spark gap. The spark gap only needs to be

momentary and if a flammable or combustible atmosphere

is present in the spark gap, the energy released can

exceed the minimum ignition energy of the surrounding

atmosphere. Uncontrolled spark discharges have enough

energy to ignite the majority of flammable atmospheres.

When liquid entering an IBC has surplus charges

attached to it, it creates an electric field which induces

opposite charges on the inner wall of the IBC. If the IBC is

not properly grounded, it will act like a capacitor plate in

an electric circuit, accumulating charges on the outer

surface of the IBC.

The accumulation of charges is now a potential ignition

hazard as surplus charges are available to discharge to

objects in the vicinity of the IBC in an uncontrolled

manner. The commonest form of object charged IBCs will

discharge too are grounded conductors like surrounding

plant equipment, dip tubes, forklift trucks and, most

commonly, the operator handling the IBC. What is of

critical importance is that the IBC is conductive and has a

low resistance static dissipative connection to earth. This

will enable any surplus charges to flow immediately to

ground from the hazardous area in a controlled manner.

The standards, including the guidance issued by the by the

SIA, categorically state this resistance must be less than

10 ohms and regularly checked to ensure the IBC is always

capable of dissipating charges.

A connection resistance of 10 ohms or less ensures

there is no doubt that the rate of charge dissipation

exceeds the rate of charge generation and charge

accumulation, allowing the static charges to be dissipated

safely from the IBC.

It follows that the first thing an operator must do before

filling or dispensing from an IBC is to ensure the IBC has a

positive static dissipative ground connection.

There are also a number of additional factors that must

borne in mind when using IBCs. Filling flow rates and the

conductivity of the liquid are especially important factors

to consider. When the IBC is filled initially, a potential

spark gap will be present between the end of the filling

pipe and the surface of the liquid. The SIA guidance

recommends 1 m/s until the fill pipe is covered by the

liquid and a limit of 2 m/s thereafter. Splash filling must

be completely avoided as this will encourage the

separation of charges.

If the liquid is conductive charges can dissipate through

the conductive wall of the earth connected IBC. If the

liquid is low conductivity (<50 pS), the appropriate charge

relaxation times should be incorporated into the handling

process. NFPA 77 provides a comprehensive list of

flammable liquid conductivities and their corresponding

charge relaxation time periods.

The IBC types

The proliferation of IBC types can complicate the

application of best practice static control procedures.

Lower cost materials like plastic IBCs are being developed

in response to the increasing cost of purchasing IBCs made

from stainless steel. It is of paramount importance to

consult experts and relevant static control guidance

documents when selecting IBCs that are potentially nonconductive.

The Solvent Industry Association guidance notice

No.51a provides clear instructions on the types of IBC to

be used depending on the solvent flash point and its

tendency to conduct or insulate charges (oxygenated or

hydrocarbons). Depending on these parameters, either

stainless steel IBCs or composites with "anti-static

sheaths" are recommended.

In any event, whatever type of IBC is used, it is of

paramount importance to ensure any conductive parts that

make up the IBC system including the filling pipe, funnels,

nozzles and dispensing cans are all bonded and connected

to a dedicated static dissipative earth with a continuous

resistance of less than 10 ohms. It also prudent to ensure

composite IBCs handling flammable materials are at least

classified as static dissipative.

Methods for demonstrating compliance

There are several ways of ensuring an IBC has a low

resistance static earth connection. The easiest way is to

provide flexible quick releasing static earthing clamps that

are designed to make positive low resistance electrical

contact with the IBC. The static earthing clamp should

have a conductive connection to a dedicated static

earthing point. It should contain a positive clamping

mechanism capable of achieving low resistance connection

to the IBC and capable of maintaining positive contact in

response to vibration effects when the IBC is being filled.

Wherever possible IBC users should specify clamps

approved for use within hazardous areas. This will provide

additional security and guarantees the clamp will do what

is designed to do – dissipate static effectively and safely.

ATEX certification guarantees clamps are not made from

material or components that could act as mechanical

sources of sparking. Factory Mutual (FM) approved clamp

tests ensure clamps are conductive to less than 1 ohm, are

capable of maintaining positive electrical contact in

response to pulling forces and cannot be disconnected due

equipment vibration. Clamps with combined FM and ATEX

certifications provide the most comprehensive and

convenient safeguards against electrostatic ignitions.

Instead of maintenance engineers regularly monitoring

and maintaining static dissipative earthing circuits and

connections, it may be more convenient to adopt the use

of self-testing static earthing clamps to offset the time

required to monitor the condition of circuits (and the risk

of not being done at all). Each time the self-testing clamp

is connected by the operator to an IBC a bright green

Light Emitting Diode flashes informing the operator the

IBC has an earth connection of 10 ohms or less. The clamp

continuously monitors the circuit between the IBC and the

designated factory earth point so should the clamp lose its

connection to the IBC the LED will stop flashing, warning

the operator of a potential fire hazard.

When a company is running processes that require

frequent or repeated filling of IBCs, it may be desirable to

add an extra dimension of safety to the options outlined

above. If an earth connection, for any reason, is

compromised the rapid generation and accumulation of

static charges in the IBC can be eliminated by cutting the

flow of material into the IBC. If the risk assessment

concludes there is a likelihood that connections have the

potential to be compromised, or not made should

operators forget to clamp the IBC, output control contacts

can be specified to safeguard against such events.

Earthing systems with output control contacts prevent the

flow of charged material into the IBC when the system

detects a lost connection.

The above measures

pertain to IBCs that are

metallic and are highly

conductive. In processes

that require static

dissipative composite IBCs,

users need to specify

earthing systems that can

monitor to the

recommended static

dissipative levels. IBC

distributors must be capable

of informing customers

whether or not the IBC is

classified as conductive or

static dissipative and what

the maximum volume

resistivity of the IBC

material is.

The main points to consider

with each of these options is

they enable companies to

demonstrate compliance with

recommended industry best

practice and provide options

to customers with different

approaches to fire risk

management of IBCs.

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