RISK ASSESSMENT · FIRE AND EXPLOSION PROTECTION
The EMKG fire and explosion module explained
The EMKG fire and explosion module derives a control level for the fire and explosion protection of an activity from a few inputs: hazard, release and quantity. It explains what the group pc-A to pc-E and the control level 1 to 3 in your risk assessment mean.
What is the EMKG fire and explosion module?
The fire and explosion module is the part of the Simple Control Approach for Hazardous Substances (EMKG) by the German Federal Institute for Occupational Safety and Health (BAuA) that estimates the fire and explosion hazard of an activity. It complements the inhalation and skin module: both modules assess the same activity, share the same quantity input and each produce their own result.
The idea is the same as the rest of the EMKG: instead of taking your own measurements, the module links the hazardous property of the substance (from its classification) with the likelihood that a fire or explosion arises (release and quantity). From this it derives one of three control levels; for a high hazard it leads straight to expert advice.
In Caventi's risk assessment you see the hazard group (as "pc-A" to "pc-E") and the control level derived from it (as "Level 1" to "Level 3" or "Expert advice") next to each activity. This page explains how both come about.
A sound assessment presupposes a correct activity description and a correct safety data sheet; if inputs are unclear or incomplete, ask the author of the data sheet or determine the values yourself. The risk assessment is the employer's responsibility and should be carried out by a competent person (for example a safety specialist or a fire-protection officer).
The fire triangle: fuel, oxygen, ignition source
A fire or explosion needs three things to come together. The module starts exactly here and asks how likely that combination is during an activity.
Fuel
The combustible substance itself - a flammable liquid, its vapour, a combustible dust or a solid. Its hazardous property follows from the classification (H/EUH statements).
Oxidiser
Usually the oxygen in the ambient air is enough. Strong oxidisers (e.g. H270/H271/H272) bring their own and sharply raise the hazard.
Ignition source
Flames, hot surfaces, sparks, electrostatic discharge and more. From control level 2 on, the measures target the avoidance of effective ignition sources.
For an explosion the fuel must additionally be finely dispersed and mixed with the oxygen - for dusts, a whirled-up dust cloud meeting an ignition source at the same time. Because temperature and pressure then rise abruptly, the extent of damage from an explosion is far greater than from a fire alone.
The inputs
The module needs three inputs. Caventi derives hazard and release automatically from the safety data sheet; you state the quantity per activity.
1. Hazard (pc-A to pc-E)
A fire and explosion hazard group is determined from the physical H and EUH statements. If several products are involved in the activity, the highest group applies ("the worst product wins").
2. Release (release group)
How quickly does a hazardous explosive atmosphere form? Liquids by boiling point or vapour pressure, solids by dustiness. Caventi determines low / medium / high.
3. Quantity
How much is handled during the activity? Small (grams/millilitres), medium (kilograms/litres) or large (tonnes/cubic metres). It is the same quantity input as in the inhalation module.
Is the module needed at all?
Before you run through the steps, an entry screening clarifies whether measures beyond the minimum standards that apply anyway (100 series) are needed. If any of the following is answered "yes", the deeper assessment is worthwhile.
Are substances with a relevant classification present (physical hazard pictograms or H statements from the H200 to H290 range plus EUH014/018/019/044; under old law the symbols E, F/F+, O or R1 to R19, R30, R44)? Are solids that are flammable by experience (paper, wood, polyethylene, polystyrene) and their whirled-up dusts handled? Is dust created, are materials worked mechanically or conveyed, or are liquids finely sprayed?
Two special rules catch unclassified but warm-processed liquids: for pure hydrocarbons (only C and H, e.g. benzene, toluene, xylene) the module applies unless the processing temperature is at all times at least 5 °C below the flash point; for hydrocarbon mixtures (e.g. petrol, diesel, white spirit) that margin must be at least 15 °C at all times. Neither rule applies to halogenated hydrocarbons.
Three further screening questions catch cases without a relevant classification: are unclassified combustible liquids used at a raised application temperature above their flash point? Are hazardous substances used that are known to burn at the prevailing application temperature, or whose substance/air mixtures are explosible (for example ammonia, chlorine or fuel-oil spray mist)? Are work procedures used in which dangerous chemical reactions can occur (for example diluting nitric or hydrofluoric acid with water, charging batteries with hazardous hydrogen formation, activities with ammonium nitrate and fertilisers containing ammonium nitrate)?
Recognising typical fire and explosion hazards
The guide names activities in which fires and explosions arise particularly often. If you recognise one of them, a closer look pays off.
- Large-area application (spraying, brushing, coating, impregnating): a large evaporation surface or fine aerosols easily form a hazardous atmosphere.
- Opening tightly closed containers, drums or plant parts holding flammable substances: the most frequent accident cause - a few millilitres of residue suffice for an ignitable atmosphere, which can ignite for example when the container is forced open with a cut-off wheel.
- Filling and decanting flammable liquids and bulk goods: ignition risk from electrostatic discharge without special measures.
- Activities with high dust release (fine dusts): very small particles form an explosive atmosphere easily thanks to their large surface.
- Activities with ignition sources (open fire, welding, cutting, grinding) and maintenance work, where operating states and ignition sources change.
Particularly affected are, among others, the chemical, wood-processing, pharmaceutical, food and feed industries, paint shops, recycling and metalworking, agriculture (biogas plants, grain silos), refineries, sewage plants and foundries.
The fire and explosion hazard group: pc-A to pc-E
The hazard group captures how dangerous a substance is with regard to fire and explosion. It is derived from the physical H/EUH statements (Gd65 Tab. 4.3); the most severe statement determines the group.
| Group | Meaning | Governing H/EUH statements |
|---|---|---|
| pc-A | Low fire/explosion hazard | Liquids and vapours without a relevant H statement - and non-explosible dusts with burning number 1-3 (Gd65 Tab. 4.4) |
| pc-B | Medium fire/explosion hazard | H226, H252, H280, H281, H290, EUH206, EUH209A - and non-explosible dusts with burning number 4-6 |
| pc-C | Raised fire/explosion hazard (easily/extremely flammable or explosible dust) | H222, H223, H224, H225, H228, H229, H251, EUH018, EUH209 |
| pc-D | High hazard: fire/explosion-capable without air or strongly oxidising - leads to expert advice | H242, H261, H270, H271, H272, EUH006, EUH014, EUH044 |
| pc-E | Very high hazard: explosive - leads to expert advice | H200, H201, H202, H203, H204, H205, H206, H207, H208, H220, H221, H230, H231, H232, H240, H241, H250, H260, EUH001, EUH019 |
Code matching is exact: EUH209 gives pc-C, while the very similar EUH209A gives pc-B. Liquids and vapours without a relevant H statement get pc-A. Because of the complexity in the individual case, groups pc-D and pc-E always lead straight to expert advice.
Where no CLP classification exists (for instance on older data sheets), the module falls back to the old-law R phrases: R10 gives pc-B; R11, R12, R18, R30 give pc-C; R5 to R9, R14, R15, R16, R44 give pc-D; R1 to R4, R17, R19 give pc-E. With combined phrases the most severe one counts. Caventi shows the triggering R phrases verbatim.
Flash point and the classification of flammable liquids
The flash point is the lowest temperature at which an ignitable vapour-air mixture can form above a liquid. The lower the flash point, the more easily flammable vapours form. Flash point and initial boiling point give the classification, which the module takes as an H statement: H224 (flash point below 23 °C and initial boiling point up to 35 °C), H225 (flash point below 23 °C and initial boiling point above 35 °C) and H226 (flash point 23 to 60 °C).
Flammable solids carry H228. CLP distinguishes two categories here (signal word "Danger" or "Warning"); the module does not distinguish them and evaluates only the H statement.
Dusts and solids without a classification
Solids often carry no physical classification. For them Tab. 4.4 of the guide applies: pc-C is chosen as a precaution, because an unclassified dust can still be explosible. If a dust explosion class (e.g. "St 1") is stated, at least pc-C applies.
Only where non-explosibility is positively established (an explicit statement such as "none" or "not explosible") may the burning number (BZ) band lower: BZ 1-3 gives pc-A, BZ 4-6 gives pc-B. A burning number alone - without that proof - never lowers a group below pc-C.
Hints about flammability or explosibility are found in safety-data-sheet sections 2.3, 5, 7 and 9, but they are rarely unambiguous; when in doubt, have the safety parameters determined by a recognised test institute (burning number and dust explosibility can also be researched in databases such as GESTIS-Staub-Ex). Non-flammable solids are e.g. sand, rock, glass or slaked lime. Caution with aluminium dusts: despite a fine grain size they can be non-explosible because of an oxide layer - but waiving explosion protection is only justified after company-specific testing of your own dust sample; when in doubt, pc-C applies.
The burning number describes the burning behaviour in six levels: BZ 1 no ignition, BZ 2 brief ignition with rapid extinction, BZ 3 local burning or smouldering, BZ 4 a spreading smouldering fire, BZ 5 a spreading open fire, BZ 6 very rapid burn-through. It is valid only for atmospheric conditions (about -20 to 60 °C, 0.8 to 1.1 bar). If no burning number can be found, the module chooses the higher group pc-B.
Where inputs are missing, Caventi deliberately errs on the safe side: if neither boiling point nor vapour pressure can be evaluated, release is assumed "medium"; if dust explosibility is excluded but no burning number is given, pc-B applies; if the physical state is unknown, pc-C applies for precaution. None of these assumptions can ever understate the hazard.
In Caventi this is the "pc-A" to "pc-E" value next to each activity; the governing H statements are shown verbatim and never translated.
The release group
The release group describes how quickly a hazardous explosive atmosphere can form. For liquids the boiling point or vapour pressure decides, for solids the dustiness (Gd65 Tab. 4.6 and 4.8).
If a boiling point is given as a range, the lowest value counts; for vapour pressure the highest - each the more volatile and therefore more conservative assumption. Where both values are available, Caventi takes the less favourable release group; the guide leaves the choice open here.
Aqueous solutions (such as household cleaners) are of low volatility: as long as they are not sprayed, release is "low". Caventi applies this relief only where the activity is explicitly marked "aqueous solution, not sprayed"; when spraying, "high" applies again.
As a rule of thumb, the finer the dust, the greater the danger; from a grain size of about 1 mm no dust explosion is to be expected. Fine abrasion from conveying, dropping or tipping granulate or granular substances does produce very fine dust, however - such activities are always assigned to release group "high".
Dust deposits sharply increase the danger: a uniform layer of less than 1 mm already suffices, when whirled up, to fill a whole room with an explosible dust-air mixture. Regular cleaning and avoiding deposits is therefore the single most important dust-explosion measure. Clean only with suitable (e.g. explosion-protected) equipment - an unprotected vacuum cleaner can itself become an ignition source.
The application temperature
The release group applies first at room temperature (about 20 °C). If a substance is processed warmer, its vapour pressure rises and with it the risk of an explosive atmosphere.
If you state a raised application temperature on an activity, the module determines the release group via the relations of Gd65 Tab. 4.7 on the boiling point: if 5 × application temperature + 50 °C is less than or equal to the boiling point, the release stays low; if 2 × application temperature + 10 °C is greater than or equal to the boiling point, it becomes high; otherwise medium.
Worked example from the guide: at a boiling point of 250 °C and an application temperature of 100 °C, 5 × 100 + 50 = 550 °C (greater than 250, so not "low") and 2 × 100 + 10 = 210 °C (less than 250, so not "high") - the release group is "medium".
If a raised temperature is stated but no usable boiling point is available, Caventi raises the release group by one step as a precaution - warmer handling can only release more. Without a temperature the room-temperature case applies (Tab. 4.6).
Quantity
The third input is the amount handled during the activity. Like the inhalation module, this module knows three quantity ranges (Gd65 Tab. 4.5):
What counts is the amount used per activity and shift, not the whole stored inventory. Decanting 0.5 litres from a 30-litre canister, for instance, is quantity band "small". For large-area application (brushing, cleaning surfaces) the amount per working day counts instead. Even very small amounts of combustible substances can form a hazardous explosive atmosphere; the larger the amount, the greater the extent of damage on ignition. When in doubt, pick the higher quantity band.
The control level: 1 to 3 and expert advice
From hazard group, quantity and release the decision table (Gd65 Tab. 4.9) gives the control level. It says what kind of fire and explosion protection is appropriate to the risk.
| Level | Measure type | What it means |
|---|---|---|
| 1 | Minimum fire-protection standards | The minimum standards suffice: basic ventilation, organisational and hygiene measures and fire protection when storing and providing substances (100-series guidance sheets). |
| 2 | Extended fire protection + ignition-source avoidance | In addition, extended fire-protection measures, emission-reducing measures and the avoidance of effective ignition sources (200-series guidance sheets). |
| 3 | Closed system + constructive explosion protection | High fire-protection measures, a closed system and constructive explosion protection (300-series guidance sheets). |
| ! | Expert advice | For a high hazard - such as self-reactive substances, organic peroxides, strong oxidisers or explosives - a fire and explosion protection specialist must be consulted. |
The higher the group, the larger the quantity and the stronger the release, the higher the level. Groups pc-D and pc-E always lead straight to expert advice.
The decision table at a glance
Hazard group, quantity and release group together give the control level. The table shows every combination for groups pc-A to pc-C; pc-D and pc-E are not in the matrix, they always lead to expert advice.
| Group | Quantity | Release group | ||
|---|---|---|---|---|
| Low | Medium | High | ||
| pc-A | Small | 1 | 1 | 1 |
| Medium | 1 | 1 | 2 * | |
| Large | 1 | 2 * | 2 * | |
| pc-B | Small | 1 | 1 | 1 |
| Medium | 1 | 2 * | 2 * | |
| Large | 2 * | 2 * | 3 * | |
| pc-C | Small | 1 | 1 | 1 liq. 2 sol. |
| Medium | 2 * | 2 | 2 liq. 3 sol. | |
| Large | 2 * | 3 | 3 | |
Worked example from the guide: pc-C, quantity "medium" and release "medium" gives control level 2 (cleaning agent H225, boiling point 57 °C, 1.5 litres).
Two cells fork by physical state: the value marked "liq." applies to liquids, the one marked "sol." to solids. For an unknown or mixed state the stricter value applies.
Groups pc-D and pc-E always lead straight to expert advice, regardless of quantity and release.
Footnote *: for pure-solid activities, the Stufe-2 fire-protection measures suffice in the marked cells. Caventi carries this as a note, never as a silent reduction of the level.
For activities with little or no air exchange (tanks, silos, pits, vessels, ducts, insufficiently ventilated rooms) the guide requires the next higher control level (1→2, 2→3). If the level thereby already reaches 3, Caventi takes the activity into expert advice as a precaution - this last step is a conservative extension by Caventi, not a requirement of the module.
Maintenance, servicing and repair work under fire and explosion hazard is generally governed by a permit-to-work procedure. This does not change the level but is added as an extra duty.
In Caventi this is the "Level 1" to "Level 3" or "Expert advice" value next to each activity.
Avoiding effective ignition sources
From control level 2 on, avoiding effective ignition sources is central. The guide names in particular:
- Flames: open fire, cigarettes, smouldering nests, welding sparks, burners
- Hot surfaces: motors, heaters, radiant heaters, hair dryers
- Electrical energy: lights, switches, bells, electrical devices
- Electric arcs during welding
- Mechanically generated sparks from spark-producing tools
- Electrostatic discharge (e.g. shoes, decanting)
- Radiation: ionising and electromagnetic (mobile phone, radio)
- Ultrasound and chemical reactions
For orientation: an explosible dust cloud is opaque and typically lies between 15 and 2000 g/m³. Flames are forbidden in all zones; tools with a constant spark shower (cut-off wheels, angle grinders) belong in no zone. How easily a dust ignites electrostatically is shown by its minimum ignition energy: normally sensitive dusts above 10 mJ, especially sensitive ones 3 to 10 mJ, extremely sensitive ones below 3 mJ - where avoiding electrostatic discharge alone no longer suffices.
The protective measures per level
Concrete guidance sheets belong to each control level. All further measures build on the minimum standards of level 1: they only work once that base is in place.
All measures follow a fixed order of priority: (1) avoid the formation of an explosive atmosphere - through substitution, limiting quantity or concentration below the lower explosive limit, extraction at the source or inertisation; (2) avoid effective ignition sources; (3) mitigate the effects of a fire or explosion as far as possible.
Because an extraction system rarely captures the substance completely, preventive explosion protection uses the zone concept: depending on how often an explosive atmosphere occurs, an area is classified (gases/vapours zone 0/1/2, dusts zone 20/21/22) and the equipment category is derived from it under the ATEX directive 2014/34/EU: 1G/1D for constant, 2G/2D for occasional, 3G/3D for short-term atmospheres. Zoning is an aid, not an obligation. The highest surface temperature of a device must always stay below the ignition temperature of the hazardous substance: for gases and vapours the temperature classes T1 to T6 (450, 300, 200, 135, 100, 85 °C) show this, for dusts the limit surface temperature marked on the device. In zones 0 and 1 a stricter limit applies: the surface temperature may reach at most 80 % of the minimum ignition temperature, and only in zone 2 does staying below the minimum ignition temperature suffice. For combustible dusts the surface temperature should stay below 2/3 of the minimum ignition temperature where a dust cloud is present, and keep a margin of at least 75 °C to the minimum ignition temperature where a 5 mm dust layer can form. For short, rare activities the guide recommends category 2G equipment.
Hot work (welding, cutting, brazing with an open flame): if ignition sources cannot be excluded, the formation of an explosive atmosphere must be safely prevented - purge containers and pipes, separate adjacent dusty areas with non-flammable partitions, and govern the work by a permit-to-work procedure. When in doubt, a substance-specifically calibrated concentration measurement confirms that the lower explosive limit is safely undershot. Permanent welding stations are raised to at least control level 2.
There is more behind "expert advice" depending on the substance: self-reactive substances and organic peroxides are sorted by their classification - type A and B (H240/H241) count as explosive and fall under explosives law, type C to F (H242) as explosion-capable. The decisive parameter is the SADT (self-accelerating decomposition temperature); because these substances react without atmospheric oxygen, the release group does not apply and the measures depend only on the quantity. Strong oxidisers (H270/H271/H272) also always lead to expert advice. Safety-critical: for substances that react with water (H260/H261), water is unsuitable as a coolant - they too always lead to expert advice.
In all cases the effectiveness check applies (Gd65 step 5): the measures taken must be checked regularly and the risk assessment documented - in Germany under Section 6(9) of the German Hazardous Substances Ordinance (GefStoffV). From level 2 on, recurring inspections are added: ventilation and extraction systems at least every 3 years, equipment for separating dusts at least annually, portable fire extinguishers every 2 years; plus a daily visual and function check where possible. These inspections belong in the hands of a competent person: relevant technical training, at least one year of experience with comparable plant in respect of explosion protection, and up-to-date knowledge; in Germany the BetrSichV requires a «befähigte Person» for this, and official recognition on top of that for equipment and protective systems in the ATEX categories. Such equipment and protective systems must also be checked before commissioning, after test-relevant modification and after every repair, not only at recurring intervals.
A separate explosion-protection document is not mandatory - what matters is that the assessment of explosion hazards, the measures and the inspection duties are documented coherently; for single activities, integration into the existing risk assessment suffices, for complex plants a separate document makes sense. The minimum documentation includes the existing explosion hazards, the precautions taken, the zoning where required, the areas with explosion-protection measures, the coordination of several firms and the necessary effectiveness checks.
What the module does not cover
The fire and explosion module has clear limits. These topics must be assessed separately:
Storage
Fire protection for the actual storage of hazardous substances follows its own rules (in Germany guidance sheet La-101, TRGS 509/510). Caventi handles joint storage elsewhere.
Plant and structures
Hazards from machinery, plant and plant parts as well as structural requirements fall under the operational-safety ordinance and building law, not this module.
Gases
Gas handling is not field-proven in the module; assess gas activities separately and involve a specialist when in doubt (in Germany TRGS 407 describes the approach). Caventi does assess gases via their H statements but marks the result as outside the proven scope.
Chemical reactions
Hazards from exothermic chemical reactions are only touched on by the module and must be considered separately.
Environmental hazards
The module does not derive substance-related hazards to the environment; these must be determined additionally.
Corrosive substances
Activities with corrosive substances (H314; strong acids with pH below 2, strong bases with pH above 11) are not covered by the module, but must be considered as a possible ignition source.
Substances arising in-process
Combustible substances that only arise during the activity or are released from articles can be assessed only if the EMKG parameters are available.
Legal framework
In Germany, assessing fire and explosion hazards is mandatory under the GefStoffV and ArbSchG; it is made concrete by TRGS 800 (fire protection), TRGS 721/722/723/727 (explosion protection) and the TRBS series, among others. For explosive substances the Explosives Act (SprengG) applies in addition; the requirements for explosion-protected equipment and for the explosion-protection document are shaped by the EU directives 2014/34/EU (ATEX) and 1999/92/EC. The EMKG fire and explosion module is a recognised BAuA aid for determining the measures needed. It remains decision support and does not replace the employer's responsibility.
How Caventi applies the module
Caventi reads your safety data sheets, derives the hazard group and release group for every product and computes the control level with guidance sheets for each activity. Per activity you maintain the quantity, application temperature, aerosol formation (spraying) and work context (low air exchange, maintenance). The burning number and the dust explosion class are taken from the safety data sheet (sections 2.3, 5, 7 and 9); if they are missing there, the cautious group pc-C stands until the value is available. The rest comes back as a traceable assessment that shows which H statements and inputs drove each group and level.
Sources
Basis: BAuA, EMKG guide module fire and explosion, 3rd revised edition 2020 (project F 2265), cited on this page in short as "Gd65". Legal frame: GefStoffV, ArbSchG, TRGS 800, TRGS 721/722/723/727, TRBS 2152.
This account is decision support and does not replace a case-by-case risk assessment or an explosion protection document. The safety data sheet governs and responsibility remains with the employer.
Frequently asked questions about the fire and explosion module
What does the group pc-A to pc-E mean?
The fire and explosion hazard group describes how dangerous a substance is with regard to fire and explosion - from pc-A (low) to pc-E (very high). It is derived from the physical H/EUH statements; groups pc-D and pc-E always lead to expert advice.
What does the control level 1 to 3 mean?
The control level says what fire and explosion protection is appropriate: level 1 = minimum standards (100 series), level 2 = extended fire protection and ignition-source avoidance (200 series), level 3 = closed system and constructive explosion protection (300 series). For a high hazard, expert advice follows.
What does "pc" stand for in pc-A to pc-E?
"pc" stands for "physico-chemical". The notation distinguishes the hazard groups of the fire and explosion module from the groups A to E of the inhalation module, which use the same letters but refer to the health hazard.
How is a solid without a classification assessed?
As pc-C for precaution, because an unclassified dust can be explosible. Only where non-explosibility is expressly established may the burning number band lower (BZ 1-3 pc-A, BZ 4-6 pc-B).
Do you need your own measurements for the module?
No. As with the rest of the EMKG, the point is precisely to determine the measures needed without your own measurements - from classification, release and quantity. For a high hazard the module points to expert advice.
The second EMKG module: inhalation and skin contact
Besides fire and explosion, the EMKG assesses the same activity for the health hazard from inhalation and skin contact - with the hazard group A to E and the control approach 1 to 4.
To the EMKG inhalation and skin moduleFire and explosion protection without a spreadsheet
Caventi assesses every activity by the EMKG fire and explosion module: hazard group and control level derived from your safety data sheets.