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).
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 (W_{arc} ) from the arc flash to the calculated PPEaA protection level (W_{arc, 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
Designation | Description | Electric arc energy / Protection level | |
---|---|---|---|
1 | Slight injury | Skin burn < 2nd degree | W_{arc} / W_{arc, prot} ≤ 1 |
2 | Reversible injury | 2nd degree skin burns Blistering, severe pain, complete healing or with scarring | 1 < W_{arc} / W_{arc, prot} ≤ 3 |
3 | Irreversible injury | 3rd degree skin burns; deeper layer skin burns | 3 < W_{arc} / W_{arc, prot} ≤ 10 |
4 | Fatal injury | 3rd degree skin burns or more severe, extensive, irreversible, with fatal consequences | W_{arc} / W_{arc, prot} > 10 |
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:
- a)
Type/condition of equipment
- b)
Technical measures
- c)
Organizational measures
- d)
Personal measures
- e)
Statistical influencing factors
- 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:
0 | Practically impossible |
---|---|
2 | Conceivable, but very unlikely |
4 | Unlikely |
7 | Seldom |
10 | Occasional 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
Designation | Description | Frequency | |
---|---|---|---|
1 | Practically impossible | Injury is not anticipated. | < 1x in 100 years |
2 | Conceivable, but very unlikely | Theoretical considerations indicate that an injury is possible, but would not be anticipated in practice, under reasonably foreseeable conditions. | 1x in 100 years |
3 | Unlikely | There is an awareness of accidents throughout industry is aware of accidents that cannot be excluded, but are very rare. | 1x in 50 years |
4 | Seldom | Injury due to electric fault arcing is quite possible. | 1x in 10 years |
5 | Occasional to frequent | Injury due to electric fault arcing should be anticipated. | monthly ... yearly |
Table A 4-3 Criteria for estimating the probability of injury
Designation | Description | Possible evaluation points (influence on PO) | |
---|---|---|---|
a) | Type/condition of equipment | Type/condition of equipment with respect to the potential bridging capacity (electric
arc formation) or the limitation of electric arc impact, e.g.
| 0 ... Practically impossible 2 ... Conceivable, but very unlikely 4 ... Unlikely 7 ... Seldom 10 ... Occasional to frequent |
b) | Technical measures | Technical measures to prevent potential bridging (arc flash formation) or to limit
electric arc impact, e.g.
| 0 ... Practically impossible 2 ... Conceivable, but very unlikely 4 ... Unlikely 7 ... Seldom 10 ... Occasional to frequent Not applicable |
c) | Organizational measures | Organizational measures to prevent potential bridging (arc flash formation) or to
limit electric arc impact, e.g.
| 0 ... Practically impossible 2 ... Conceivable, but very unlikely 4 ... Unlikely 7 ... Seldom 10 ... Occasional to frequent Not applicable |
d) | Personal measures | Personal measures to prevent potential bridging (arc flash formation) or to limit
electric arc impact, e.g.
| 0 ... Practically impossible 2 ... Conceivable, but very unlikely 4 ... Unlikely 7 ... Seldom 10 ... Occasional to frequent Not applicable |
e) | Statistical influencing factors | Statistical influencing factors that play a role when evaluating the probability of
electric arc occurrence or injury due to electric arcing, such as
| |
f) | Ergonomic influencing factors | Ergonomic influencing factors that play a role when evaluating the probability of
electric arc occurrence or injury due to electric arcing, such as
| 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):
Fig. A 4-3
Risk matrix with a summation of evaluation points