ISKRIT / Environment & safety / Fire hazard category
Environment & safety
Fire load density, explosion overpressure and hazardous zone class
Material masses and net calorific values give the fire load density in MJ/m2, the released substance gives the explosion overpressure in kPa, and the two together decide the category of the room and of the building. The zone class is determined separately, from the medium and how often an explosive mixture appears.
Data current as of 2026-08-24
Standards
SP 12.13130.2009 annexes A and B: overpressure by formula A.1 for gases and vapours and by A.2 for suspended dust, categories V1 to V4 by the specific fire load of table B.1, building category by section 6. Zone classes per federal law 123-FZ articles 18 and 19; the zone numbering 0, 1, 2 for gas and 20, 21, 22 for dust is the same as in IEC 60079-10.
Input
The substance and the mass released in an accident, room volume and temperature, material masses with their net calorific values and the floor area, the medium and how often an explosive mixture appears. A whole schedule of rooms can be loaded from your own Excel with the columns confirmed on import.
Output
Explosion overpressure in kPa, specific fire load in MJ/m2, the room category with its justification, the building category, the zone class with the article it rests on, an XLSX register and A5 signs ready to print.
What it does
- Fire load density qf = sum of mass times net calorific value over the floor area, the EN 1991-1-2 formula
- Explosion overpressure with the stoichiometric concentration and vapour density derived from the molecular formula, not guessed
- Room category A, B, V1 to V4, G, D, with the clause each verdict follows from
- Building category from the room schedule, with the sprinkler relaxation applied
- Zone class 0, 1, 2 for gas and vapour, 20, 21, 22 for dust, P-I to P-III for fire-hazardous areas
- Printable register and A5 category signs for the whole facility
The tool and the platform
The tool
- Room and building category, hazardous zone class and the calculation behind it
- Load substances from Excel, export to XLSX, printable schedule and door signs
- Calculations are stored on the server and reopen next time, company letterhead with signatures
- Works instantly, no sign-up required
ISKRIT·HSE made to order
This platform does not exist yet: we build it around your workflow. Here is what goes into it.
- Register of the rooms and buildings of the plant with category history
- Category review after a technology change, with a notice to the officer
- Linked to the hazard register and to site instructions
Questions
How is fire load density calculated?
qf is the sum of each material mass times its net calorific value, divided by the floor area, which is the same formula as EN 1991-1-2. The area is taken as not less than 10 m2 per clause B.4, and the calorific values come from your material data sheets rather than from a built-in guess.
What defines categories A and B?
An explosion overpressure above 5 kPa. Gases and flammable liquids with a flash point at or below 28 C give category A, the other combustibles at the same pressure give B.
How are V1 to V4 assigned?
By the specific fire load on the area under consideration: above 2200 MJ/m2 is V1, 1401 to 2200 is V2, 181 to 1400 is V3, and 1 to 180 is V4. V2 and V3 are raised one step when the load sits close to the roof trusses, checked by the inequality Q >= 0.64 times gt times H squared.
Does the tool give the extent of the zone in metres?
No. The zone number follows from how often and how long the explosive mixture is present, which is what article 19 asks for. The extent in metres is a separate quantitative calculation under IEC 60079-10-1 through the hypothetical volume Vz, and this tool does not claim it.
What if there is no inventory of materials yet?
Pick the occupancy of the room and the tool shows the typical fire load density from EN 1991-1-2 table E.4, both the average and the 80% fractile, together with the category to expect. It stays an order of magnitude: the typical value never enters the category calculation, which runs on actual masses.