What does it look like in the event of an explosion hazard?
According to the ATEX User Directive, for workplaces containing explosion hazard zones, an ‘Explosion protection document’ must be prepared, its main purpose is to assess the risk of explosion. Thanks to this, we sometimes find out that despite the classification of the zone, the risk of explosion is negligible, because, for example, the minimum ignition energy will never occur in the given conditions of processing, storage or transport of a flammable substance, so there will be no ignition and explosion. A good example here is e.g. PVC powder, which during pouring or pneumatic transport creates explosive atmospheres according to the definition, however, they can be set on fire practically only with open fire or red-hot surfaces, which are usually not found in storage facilities or technological installations. Breaking the rules of fire safety is not taken into account. This is what the training, control and order services are for, and they provide organizational security.
Therefore, there is no need to use EX components in these installations, because they will not constitute an effective source of ignition or be afraid of static electricity, which is dangerous in most operating conditions up to the value of 500 mJ, and a large part of the dust has a minimum ignition energy value much above 1000 mJ.
The same happens with the flash point of liquids, which for some of them is above 50 ° C and to which these liquids are not heated in the technological process or during storage / transport, as a result these liquids do not pose any significant explosion hazards in such conditions, although in their safety data sheets contain information on similar hazards.
It should be mentioned because the assessment of the actual explosion risk allows to adopt technical and organizational protection appropriate to a given case, which significantly increases the effectiveness of the money spent by investors and understanding why it should be done.
And what does it look like with fire hazards?
Unfortunately, the law does not provide similar procedures to assess the risk of a fire, which is a mistake, especially in production and storage facilities, especially in industrial / technological facilities.
Legal requirements for fire protection are defined on the basis of several rigid parameters, which make it difficult to adapt them flexibly to real needs.
In Poland, the height of the object (for multi-storey buildings) and the value of the fire load density are the main criteria for selecting protections in production and storage facilities. On their basis, the following are defined:
- The fire resistance class of the building, and consequently the fire resistance class of the building elements.
- The maximum area of the fire zone.
- Maximum lengths of passageways and escape routes.
- Minimum distances from other buildings and the property line.
The height of a multi-storey building has a real impact on the evacuation conditions and conducting rescue and firefighting operations, however, it happens to a very different extent and depending on the real fire hazards, which will be described below.
From the fire load density value, it is only possible to deduce the maximum amount of energy that can be emitted during the combustion of combustible materials in a given fire zone.
Theoretically, under full combustion conditions, without taking into account:
- at what rate will this energy be emitted,
- what will be the real dwell time, which will be different depending on burned material and the conditions prevailing during combustion (the relative duration of the fire specified in the PN-B-02852 standard is very “relative” and may be far from reality).
For example, a fire of paper stored in rolls standing vertically in accordance with NFPA 204 is classified as ultra-fast and develops approximately 20 times faster than paper products densely packed in cartons and stored on shelves.
This means that the difference in the development of products having the same heat of combustion and determining a similar value of the fire load density may be twentyfold, which means that e.g. in a warehouse of paper products people will have much longer time to evacuate than in a warehouse of paper rolls, where several minutes after the outbreak of the fire, it will probably be impossible to carry out the firefighting operation. The fire load density in both warehouses will be similar, and the requirements for fire protection will also be similar, although the risks are completely different. It should also be noted that according to the PN-B-02852 standard, paper in rolls generates less risks than paper in reams, because only 10% of its weight can be included, and for paper in reams – 20% (no information about paper products so 100% of its mass should be taken into account).
Another example is a warehouse of PVC plates, which, taking into account their mass and heat of combustion, can determine a relatively high level of fire load density for a given fire zone of the warehouse. Has anyone tried to set fire to a PVC plate? It is difficult, and under storage conditions it can practically only happen from a fire with another combustible material. And what about a warehouse only for PVC (plates, fittings, etc.) in a multi-storey building of these plates? The level of fire load density is high, while the risk of ignition of this material is practically negligible.
There are many more similar to the above examples, where:
- Legal requirements are too low – example of a warehouse of paper in rolls,
- Legal requirements are too high – example of a PVC plates warehouse.
The above is the result of defining hazards in production and storage facilities primarily based on the fire load density parameter, which, as can be seen in the cursory analysis, shows the actual hazards very inaccurately.
The best solution to this problem is the introduction to the legal system of a fire risk assessment and its effects, similar to the ATEX User Directive. One may notice that it is currently possible to use substitute and substitute terms, however this is an imperfect formula for the following reasons:
- Applies only to some areas of legal requirements.
- It is discretionary and often resembles an auction (which should be given in exchange) and this does not correspond to the examples above.
- Significantly extends the design process.
- It involves state offices (National Fire Service or the Ministry) in this process, making them also involved in responsibility, which, with a very large variety of technological processes, hazards in production and storage facilities and staff limitations in offices, significantly hinders the possibility of an in-depth technical discussion.
Assessment of the risk of fire in production and storage facilities
This risk assessment should consist of:
- Identification of fire hazards divided into fire zones.
- Presentation of fire development in each of the fire zones based on recognized (previously defined) standards / guidelines – the presentation should contain a descriptive part supported by calculations and / or a computer model made in accordance with previously defined global guidelines (in case of national guidelines). The calculation of the fire development should take into account the adopted fire protection (technical and passive) and the rules of conduct in case of a fire. This presentation should take into account all significant risks presented over time, i.e .:
- thermal impact,
- emission of toxic substances,
- spread of fire to other buildings,
- other negative impacts on escape routes,
- any other hazards (chemical, construction or explosions) resulting from damage caused by fire, e.g. collapse of a flyover with pipelines containing toxic or flammable substances, etc.
- Presentation of the evacuation conditions according to the fire development presentation.
- Presentation of the conditions for conducting rescue and firefighting operations in accordance with the fire development presentation.
- Presentation of the possibility of the fire spreading to other facilities in accordance with the presentation of the fire development.
- Performing a risk assessment for individual fire zones and / or the entire building / facility together with recommendations.
The author of the risk assessment should be a firefighter with the support of technologists who are responsible for the way the facility is used.
The document should be reviewed by industry designers (architect, building constructor, installer, electrician) and then agreed by a fire safety and construction appraiser. The purpose of the agreement is to confirm that the legally required fire protection objectives in terms of evacuation conditions, rescue operations and fire spreading will be met.
The document should also be agreed with the planned investment insurer.
For small or typical production and storage facilities, the current legal path can be left without the need to perform a similar risk assessment, where the design is based on the requirements contained in legal acts.
For other investors / design offices, an alternative solution can be given in the form of risk assessment, which will ultimately constitute the basis for design.
I would make an arrangement with the insurer obligatory, because I know from experience that the company insuring both the facility, property inside, goods and accident or third party liability insurance poses much more serious requirements than legal conditions, but they are usually better suited.