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

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Annex 4 - Application of the Risk matrix

A 4.1
General

Many years of practical operational experience with PPEaA generally reveal that, when PPEaA was properly worn, injuries have not resulted from electric arc incidents - even at times when the calculated PPEaA protection level had been exceeded. This shows that the calculation methodology (Section 3 Phase 3) usually incorporates sufficient safety reserves, especially because, in many cases, the partially assumed worst-case conditions are not all present at the same time.

Moreover, those not directly quantifiable influencing factors, such as personnel qualifications, the use of bypass-resistant equipment or the absence of arc flash propagation options, could have significantly reduced the risk of injury due to electric arcing without the factors having been depicted in a calculation methodology to date.

With the expanded approach to the Risk assessment described in the following text, further measures (technical, organizational, personal) and influencing factors (statistical, ergonomic) that go beyond the numerical arithmetic parameters previously evaluated are now considered (Fig. A 4-1).

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Fig. A 4-1
Overall evaluation of the influencing factors results in the electric arc hazard

The Risk assessment opens the possibility of allowing for the calculated PPEaA protection levels to be exceeded under certain conditions within specified limits if the resulting risk of injury is sufficiently low. This is achieved through the use of a Risk matrix (Section 3, Fig. 3-2) and the application methods described below The residual risk of an injury due to electric fault arcing is the link between the anticipated severity of injury and the anticipated probability of injury - while accounting for the respective measures adopted.

The Risk matrix can be applied only when the results of the calculation process (Section 3, Phase 3) exceed the calculated PPEaA protection level. An estimation is then made of the probability of electric arcing and the severity of related injury after the adopted measures have been implemented.

The resulting residual risk is then evaluated (Risk matrix):

"green":Work activities may be carried out
"yellow":Work activities may be carried out, but active risk management is required:
-The risk is to be maintained as low as reasonably practicable (ALARP) according to DIN EN 31010 (VDE 0050-1),
-Case-by-case evaluation,
-Regular inspections to determine whether further technical, organizational or personal measures are possible,
-Specify a cycle, if applicable
"red":Work activities must not be carried out under these circumstances:
-Implement further measures according to Phase 5, if applicable,
-The installation may need to be isolated, if
applicable.

A 4.2
Evaluation of the anticipated severity of injury

The anticipated severity of injury due to an electric arc occurrence must be evaluated with consideration given to all adopted safety measures. The most serious personal risks are associated with the thermal effects of electric fault arcing.

The degree of severity of a burn is generally dependent on a multitude of complex factors, such as the intensity and the duration of the heat flow acting upon the surface of the skin and the resulting rise in temperature at the different layers of the skin. In this methodology, a simplified estimation is made of the anticipated severity of injury using the relationship of the expected arc energy (Warc ) from the arc flash to the calculated PPEaA protection level (Warc, prot ) corresponding to the following Table A 4-1.

Remark 1:

The values specified in Table A 4-1 are based on a review of literature and determinations made by the Electric fault arc working group, and maintain a safety distance that is deemed sufficient by experts.

Remark 2:

This DGUV Information does not address potential hazards associated with the collateral effects of an arc flash, such as those due to pressure, acoustic shock, particles flying off, radiation, molten particles or gases. These hazards must be considered separately, if applicable.

A 4.3
Evaluation of the probability of occurrence

When using the Risk matrix, the anticipated probability of an injurious occurrence (PO) due to electric fault arcing (EFA) must be estimated with consideration given to all adopted measures. The anticipated probability of injury thereby will be influenced by both those measures adopted to prevent the occurrence of electric arcing, as well as those measures adopted to prevent the effects of a potential arc flash (Fig. A 4-2).

The possible categories for the probability of injury due to electric arcing are listed in Table A 4-2.

Table A 4-1 Evaluation criteria for determining the potential severity of injury

DesignationDescriptionElectric arc energy / Protection level
1Slight injurySkin burn < 2nd degreeWarc / Warc, prot ≤ 1
2Reversible injury2nd degree skin burns Blistering, severe pain, complete healing or with scarring1 < Warc / Warc, prot ≤ 3
3Irreversible injury3rd degree skin burns; deeper layer skin burns3 < Warc / Warc, prot ≤ 10
4Fatal injury3rd degree skin burns or more severe, extensive, irreversible, with fatal consequencesWarc / Warc, prot > 10
g_bu_1890_as_28.jpg

Fig. A 4-2
Influence of the measures adopted to prevent the effects of potential electric fault arcing

The probability of injury due to electric arcing can also be differentially estimated on the basis of detailed evaluation criteria (Table A 4-3). For this, evaluation points are used that are assigned to the evaluation criteria below:

  1. a)

    Type/condition of equipment

  2. b)

    Technical measures

  3. c)

    Organizational measures

  4. d)

    Personal measures

  5. e)

    Statistical influencing factors

  6. f)

    Ergonomic influencing factors

The sum of the evaluation points results in a value that can be used to help determine the probability of occurrence (refer to Fig. A 4-3).

Each criterion considered should be evaluated with respect to the activity/activity group performed and to the existing installation/type of equipment, as well as to its interaction with other criteria according to Table A 4-3.

Evaluation points 0 to 10 should be assigned based on how much influence the respective criterion has on the probability of injury.

Influence leads to the probability of injury:

0Practically impossible
2Conceivable, but very unlikely
4Unlikely
7Seldom
10Occasional to frequent

If a criterion does not apply (e.g. an appropriate measure is not possible, statistical data is not available, etc.), the value of the evaluation points for this criterion should be set into the average value of the other criteria evaluated so that the results will not be distorted.

Example:

Criterion a)... 4 points
Criterion b)... not applicable
→ Value will be set to 3.5 points
Criterion c)... 2 points
Criterion d)... 4 points
Criterion e)... not applicable
→ Value will be set to 3.5 points
Criterion f)... 4 points

The evaluation of criteria a, c, d and f together results in 14 points. The value of the not applicable criteria b and e is set to a value of 3.5 (= 14/4: the average value of the 4 other criteria).

Table A 4-2 Anticipated average frequency of injury of an employee after implementing the adopted measures

DesignationDescriptionFrequency
1Practically impossibleInjury is not anticipated.< 1x in 100 years
2Conceivable, but very unlikelyTheoretical considerations indicate that an injury is possible, but would not be anticipated in practice, under reasonably foreseeable conditions. 1x in 100 years
3UnlikelyThere is an awareness of accidents throughout industry is aware of accidents that cannot be excluded, but are very rare. 1x in 50 years
4SeldomInjury due to electric fault arcing is quite possible.1x in 10 years
5Occasional to frequentInjury due to electric fault arcing should be anticipated.monthly ... yearly

Table A 4-3 Criteria for estimating the probability of injury

DesignationDescriptionPossible evaluation points (influence on PO)
a)Type/condition of equipmentType/condition of equipment with respect to the potential bridging capacity (electric arc formation) or the limitation of electric arc impact, e.g.
  • Open, bridging potential (potential distances, bridging capacity, e.g. through tooling/accessories or falling conductive parts, if applicable)

  • Separation from adjoining panels/separation of potentials (e.g. division bars)

  • Contamination, moisture, growth

  • Maintenance and testing

  • Age of the installation

  • Particular environmental concerns (e.g. climatic conditions)

  • Installation with closed doors

  • Protection against physical contact (e.g. VDE 0660-514)

  • Low voltage equipment according to VDE 0660-600-2, Supplemental sheet 1 (Electric arc tested equipment)

  • Base point-free low voltage equipment

  • Medium voltage equipment according to VDE 0671-200 (Electric arc tested equipment)

  • Switching fault protection

0 ... Practically impossible
2 ... Conceivable, but very unlikely
4 ... Unlikely
7 ... Seldom
10 ... Occasional to frequent
b)Technical measuresTechnical measures to prevent potential bridging (arc flash formation) or to limit electric arc impact, e.g.
  • The use of tools or equipment (with regard to protection against bridging, distance)

  • The use of protective and auxiliary resources

  • The condition of work resources

  • The use of measuring devices (e.g. suitable measurement category)

  • Active electric arc protection system

  • Safe work fuses

  • Monitoring of the effectiveness of the technical measures

0 ... Practically impossible
2 ... Conceivable, but very unlikely
4 ... Unlikely
7 ... Seldom
10 ... Occasional to frequent Not applicable
c)Organizational measuresOrganizational measures to prevent potential bridging (arc flash formation) or to limit electric arc impact, e.g.
  • Organizational rules (e.g. operating/work instructions):
    Responsibilities
    Protective measures against electric fault arc (e.g. testing for fault-free status)
    Teaching/training
    Verification of effectiveness
    Equipment documentation
    Rules of entry for electrical installations
    Instruction related to electrical equipment

  • Dealing with electrical accidents/incidents:
    Analysis/Communication
    Measures/Monitor the effectiveness of measures

  • When performing switching operations:
    Operational rules/Organization of switching operations
    Documentation of switching operations
    Switching qualification/Switching authority
    Retention of qualifications

  • When performing live work: Instructions for live working (protection measures against electric arcing)
    Qualified electricians as instructors
    Special training
    Retaining qualifications
    Control (quality assurance)

  • Dealing with outside personnel:
    Requirements/Prequalification
    Instruction/training
    Retaining qualifications
    Control (quality assurance)

0 ... Practically impossible
2 ... Conceivable, but very unlikely
4 ... Unlikely
7 ... Seldom
10 ... Occasional to frequent Not applicable
d)Personal measuresPersonal measures to prevent potential bridging (arc flash formation) or to limit electric arc impact, e.g.
  • The use of PPEaA The selection of PPEaA (Arc protection class)
    Application/Testing (e.g. visual inspection) Routine care, maintenance and repair
    Verification of usage/Quality assurance

  • Qualification of operative personnel: Activity-specific/equipment-specific knowledge
    Work methods and experience
    Instruction
    Special qualifications (e.g. switching qualification, live working)
    Retention of qualifications
    Monitoring of qualifications

0 ... Practically impossible
2 ... Conceivable, but very unlikely
4 ... Unlikely
7 ... Seldom
10 ... Occasional to frequent Not applicable
e)Statistical influencing factorsStatistical influencing factors that play a role when evaluating the probability of electric arc occurrence or injury due to electric arcing, such as
  • Accident statistics
    (e.g. the frequency of accidents on the basis of in-house operational experience or known accidents and statistical data)

  • Further stochastic factors
    (e.g. the frequency/duration of activities with exposure to electric arcing, task-related: e.g. voltage testing of equipment that has already been isolated)

f)Ergonomic influencing factorsErgonomic influencing factors that play a role when evaluating the probability of electric arc occurrence or injury due to electric arcing, such as
  • PPEaA
    Wearing comfort (e.g. Fit, hygiene, tactility)
    Wearing acceptance

  • Work environment (e.g. freedom of movement, forced posture, lighting, climatic conditions)
    Psychological stress (e.g. Time pressure, diversions)

0 ... Practically impossible
2 ... Conceivable, but very unlikely
4 ... Unlikely
7 ... Seldom
10 ... Occasional to frequent Not applicable

The sum of the evaluation points for the criteria a) to f ) results in the classification of the anticipated probability of injury in the Risk matrix (Fig. A 4-3):

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Fig. A 4-3
Risk matrix with a summation of evaluation points