DGUV Information 203-077e - Thermal hazards due to electric fault arcing Guide for selecting Personal protective equipment

Personal protective equipment against the thermal effects of an electric fault arc (PPEaA)

Personal protective equipment against the thermal effects of an electric fault arc (PPEaA) applies to any item meant to be worn or held by a person for protection against the thermal hazards associated with electric fault arcing.

Work

Any form of electrotechnical or non-electrotechnical activity where the potential for an electrical hazard exists.

Live working

Any work-related activity, because of which a person, either physically or through the use of tooling, equipment or devices, knowingly comes in contact with or enters a danger zone associated with live components according to VDE 0105-100.

Work performed in the vicinity of live components

All work-related activities, because of which a person, either with parts of the body or through the use of tooling or other objects, enters the vicinity zone according to VDE 0105-100 without entering a danger zone according to VDE 0105-100.

Working distance a

Working distance a is the distance between the electric fault arc and the operative part of a person's body (torso) while performing work or while present in the working environment under consideration.

Note 1 regarding the term:

Working distance is denoted in mm.

Equivalent arc energy

The protection level of the PPEaA W_{arc, prot} resulting from the test level W_{arc, test} at a fixed working distance a, as well as the transmission factor k_T.

Note 1 regarding the term:

Equivalent arc energy is denoted in kJ or kWs.

Note 2 regarding the term:

Equivalent arc energy was denoted with W_{arc, prot}in the 2012 Edition of this DGUV Information.

Normalized arc power k_P

The relationship of electric arc power to short-circuit power in the electrical network at the fault location. k_P considers the physical properties of "electric arc voltage" and "electric arc current".

Sustained short-circuit current I_kDC

The stationary value of short-circuit direct current with a bolted short-circuit at the fault location.

Note 1 regarding the term:

Sustained short-circuit current is denoted in kA.

Direct incident energy E_i0

Heat energy emanating directly from the electric fault arc per unit of affected area.

Note 1 regarding the term:

Direct incident energy is denoted in kJ/m²or kWs/m²(cal/cm²). 1

Transmitted incident energy E_it

Incident energy that penetrates PPEaA due to electric arc exposure; a portion of the direct incident energy.

Note 1 regarding the term:

Direct incident energy is denoted in kJ/m²or kWs/m²(cal/cm²). 1

Incident energy E_i

The heat energy (total heat quantity) impacting an exposed surface in a certain distance as a result of electric fault arcing.

Note 1 regarding the term:

Direct incident energy is denoted in kJ/m²or kWs/m²(cal/cm²). 1

Electrical system

Overall electric installations and equipment used for producing, transmitting, converting, distributing and utilizing electrical energy.

Electrode gap d

Distance between the arcing electrodes.

Note 1 regarding the term:

The electrode gap is denoted in mm.

Short-circuit duration t_k

Period of the short-circuit in time.

Note 1 regarding the term:

Short-circuit duration is denoted in s.

Short-circuit power P_k(DC range) or S"_k(AC range)

A virtual value calculated as a product of the prospective short-circuit current at a point on the network and the nominal network voltage (or contracted supply voltage). For three-phase AC systems, the factor √3 is to be accounted for; the short-circuit current corresponds to the 3-phase initial short-circuit AC current I"_k (VDE 0102 [8]).

Note 1 regarding the term:

Short-circuit power is denoted in kVA (AC) , kW (DC).

Arc duration t_arc

Period of the electric fault arc in time.

Note 1 regarding the term:

Arc duration is denoted in s.

Electric arc energy W_arc

Electrical energy that causes electric arcing and is converted into an arc flash.

Note 1 regarding the term:

Electric arc energy is calculated as the sum (integral) of the product of the instantaneous values of arc voltage and arc current, as well as the time differential developing over the duration of arcing. In three-phase AC systems, the electric arc is generally a multi-pole (usually three-pole) fault; the arc energy in this context is the total energy of all contributing electric arcs.

Note 2 regarding the term:

Electric arc energy is denoted in kJ or kWs.

Electric arc short-circuit current I_{k, arc}

Current (due to electric arcing) actually flowing (through the arc) at the fault location throughout the arc duration.

Note 1 regarding the term:

The electric arc short-circuit current is determined as the average effective value over the duration of the short-circuit (AC) or the average value over the virtual steady-state phase of the short-circuit (DC).

Note 2 regarding the term:

Electric arc short-circuit current is denoted in kA.

Electric arc power P_arc

Active power converted into electric arcing; a product of the electric arc current and the electric arc voltage.

Note 1 regarding the term:

Electric arc power is denoted in kW.

Materials

Textile fabrics or other materials used to produce single or multilayer PPEaA.

Prospective short-circuit current

Expected current that flows when a fault location is short-circuited through a conductor with negligible impedance (bolted short-circuit of the electrical supply).

Note 1 regarding the term:

Prospective short-circuit current is denoted in kA.

Note 2 regarding the term:

There is a basic difference between the actual electric arc short-circuit current and the prospective short-circuit current. The actual electric arc short-circuit current flowing throughout the arc duration is lower and fluctuates due to the non-linear arc impedance that varies indeterminately over time.

Test level W_{arc, test}

Electric arc energy set as part of the Box test (according to VDE 0682-306-1-2 [11]) for either of the two electric fault arc test categories and leading to a direct incident energy E_i0P .

Note 1 regarding the term:

The test level is denoted in kJ or kWs.

Test current I_APC

Prospective short-circuit current in the electrical test current circuit (expected) used for setting a test category in the Box test method; effective value (symmetrical AC component).

Note 1 regarding the term:

Test current is denoted in kA.

Residual risk

The risk of personal injury that remains due to electric arc exposure - after the measures aimed at preventing an electric arc occurrence and its effects have been implemented. Residual risk results from the combination of

• the anticipated severity of injury and the

• probability of injury, while accounting for the respective adopted measures.

R/X-ratio

Relationship of the ohmic resistance to the inductive reactance of a short-circuit electrical circuit.

PPEaA protection level W_{arc, prot}

Electric arc energy level, up to which the PPEaA offers protection against the thermal effects of electric fault arcing; the PPEaA parameters with a given transmission factor k_T and working distance a; correspond to the equivalent arc energy.

Note 1 regarding the term:

Protection level is denoted in kJ or kWs.

Stoll curve

Correlation between thermal incident energy and exposure time derived from data related to the tolerance behaviour of human skin when exposed to heat; specifies the limits for the occurrence of second-degree skin burns.

Current limiting factor k_B

Relationship between the actual electric arc short-circuit current and the prospective short-circuit current.

Electric fault arc

A self-sustaining gas discharge due to a faulty connection between conductive components of different potential in an electric installation.

Note 1 regarding the term:

Electric fault arcing in the context of this DGUV Information is considered to be an undesirable faulty occurrence caused by short-circuiting.

Arc protection class APC

Categories of thermal protection afforded by PPEaA against the thermal effects of an electric fault arc, as tested using the Box test method (according to VDE 0682-306-1-2 [11]). Arc protection classes (APC) are distinguished by the tested energy levels (W_{arc, test} und E_i0P).

T-O-P principle

The T-O-P principle determines the order of priority of the protective measures implemented by a company to protect its employees against hazards: first technical, then organisational and lastly personal measures.

• Technical measures

  Safety-relevant installation and maintenance of machinery and equipment, operating facilities, working and social areas.

• Organizational measures

  Rules to facilitate safe working practices, such as operating instructions and safety-related information.

• Personal measures

  Personal protective equipment, qualifications (e.g. special training or instruction).

Transmission factor k_T

A factor describing the spatial propagation of the thermal impact of an electric arc on the working environment. It is determined by the geometric relationships between the installations at the work location.

Transmission and exposure conditions

Totality of the influences on the heat transfer associated with an electric fault arc.

Initial short-circuit current I"_k

The effective value of the short-circuit current's AC component at the beginning of the short-circuit event in an AC or a three-phase AC installation (AC system) with bolted short-circuiting.

Note 1 regarding the term:

Initial short-circuit AC current is denoted in kA.

Note 2 regarding the term:

A maximum value I"_{k max}and a minimum value I"_{k min}of the initial short-circuit AC current are determined in the standardized short-circuit current calculation.

Nominal network voltage U_Nn

Voltage between the conductors intended for a network, by which the network is designated or identified, and which pertains to specific operating characteristics.

Note 1 regarding the term:

Nominal network voltage is denoted in V.

Electric arc voltage U_arc

Average value of the voltage associated with an electric fault arc that occurs between the electrodes (conductors).

Note 1 regarding the term:

Electric arc voltage is denoted in V.

Time constant τ

A measure of the current reaction time with a change in voltage, dependent upon the L/R ratio in the electric circuit.

Note 1 regarding the term:

Time constant is denoted in ms.

Threshold energy W_{arc, min}

The threshold value of electric arc energy (50 kJ), beyond which the use of PPEaA is required.

Table 2-1 Symbols and units