Research in the field of evaluation of anfo explosive preparation installations, Tests and results

The technical-economic efficiency of rock extraction works depends significantly on the drilling and blasting works as well as the adjacent costs. The cost of the explosive is an important component in these and the generalization of the widespread use of the use of bulk explosives (ANFO) has generated a significant reduction in the cost. Making the explosive close to the place of use in fixed or semi-stationary installations on the quarry stage eliminates the costs related to storage or long-term storage, transport, escort, security. However, installations for the manufacture of ANFO type explosives must consistently produce a simple quality explosive mixture. The quality lies in the participation of the precursors as well as in the degree of homogenization, stability and a good behavior to external stimuli that can lead to sensibility to initiation stimuli or inhibition of sensitivity where the harmful influence of moisture in the raw material or environment must be emphasized. The paper presents tests and results obtained in recent years for such installations used by several companies in Romania performed under the supervision of INSEMEX specialists. These assessments were completed with the certification of explosives manufacturing facilities for the specified operating parameters as well as for explosives.


Introduction
An explosive material, or explosive substance, is a substance (or mixtures of substances) that is in a metastable state, capable of suffering under the action of heat or a mechanical factor, an explosive transformation that reacts rapidly, decomposes suddenly and violently with development. strong heat, light and gas, causing a large increase in pressure in its environment. Explosives for civilian use belong to the category of dangerous products, representing a significant risk of explosion when stored and handled under conditions of exposure to high temperatures. ANFO type explosives are low power explosives with a low sensitivity to external actions. The main risks associated with the use of explosives for civilian use are those of uncontrolled explosion, fire or poisoning with combustion products. The importance of the field is argued by the fact that for explosives for civilian use, the European Union has promoted Directive 2014/28 / EU, which regulates the placing on the market of these products. In the said Directive there is a technical requirement regarding the safety of explosives which must be assessed before placing on the market, by testing the products according to harmonized standards with the aim of ascertaining the conformity / non-compliance with the relevant safety requirements. These tests are performed in RENAR accredited test laboratories, based on harmonized European Standards. As a result, we mention some of the most important tests that were carried out within the INSEMEX Laboratories, having as object ANFO type explosives: -Detection and measurement of toxic explosion gases; -Determining the impact sensitivity of explosives and detonating cords; -Verification of the friction sensitivity of the blasting explosives and the core of the detonating wicks; -Determining the percentage participation of the precursors in the product made with a mobile / fixed explosive manufacturing unit. • DETECTION AND MEASUREMENT OF TOXIC EXPLOSION GASES. This test is performed in a special stand called a gas chamber in which the test sample is inserted and detonated. Following this operation, the amount of gas resulting from the Testo 350 XL plus testo easy Emission Software is measured. The results are listed in table no. 1 and are compared with the technical specification of the explosive.

Determination of the sensitivity to impact of explosives and detonating cords
The impact sensitivity of explosives is a test of high importance in terms of explosive safety and is performed on the stand called BAM type hammer. The test consists of introducing a volumetrically measured quantity of ANFO type explosive between two pellets which in turn are inserted into the anvil of the test stand. Determine the minimum height specified by the manufacturer and release the weight, following whether or not a reaction has occurred. The positive result can be recorded as a result of an explosion noise with or without breaking the housing, but there can also be a specific smell of generated gas, light and when the assembly changes the color of the explosive material left in the situation of incomplete explosion. The results are listed in Tab

Determination of the percentage participation of precursors in the made product with a mobile / fixed unit of explosive manufacture
The principle of the method consists in making the mixture of porous ammonium nitrate and diesel made on a mobile or stationary installation. The frame subassemblies of an ANFO type explosive plant mounted on a MERCEDES BENZ truck chassis are: -supply tank / bunker for porous ammonium nitrate; -helical / auger conveyor, placed at the base of the supply bunker; -cellular dispenser; -flexible pneumatic transport pipe of the ANFO explosive mixture in the boreholes; -hydraulic drive unit; -diesel injection circuit; -compressed air supply group; -command and control circuits. 11.This Certificate is issued to the applicant in point 4, for the type of product in point 3, manufactured at the address referred to in point 6 and may be reproduced only in its entirety without any modification. 12. The marking of the product must include the following: CE 1809 The explosives shall be placed on the market in the European Community on the basis of the CE conformity marking, followed by the identification number of the notified body INSEMEX -SECEMTI, in accordance with the "Regulation for the affixing of the conformity marking and identification number" RAM, ed. 3  (7) The holder / owner of the installation, to which this certificate refers, is responsible for compliance with the specifications and specifications in the ANNEX. Any modification to the installation shall be made only with the prior written consent of the body which issued this certificate. (8) This certificate is valid for three years from the date of issue, unless it is suspended or withdrawn in advance if it is found that the holder or the product no longer meets the certification requirements. This certificate is legally valid only with the official address INCD-INSEMEX, may be used only for the product referred to in point 3, only for the applicant with the address referred to in point 4 and may be reproduced only in its entirety without any modification. • The holding company will elaborate a standardized form of "Work permit" which will include the list of checks of the tractor and the installation.

INCD-INSEMEX PETROSANI EXPLOSIVES CERTIFICATION SERVICE, MEANS SHOOTING AID AND TECHNIQUES -INSEMEX SECEMTI -
• Before each use it is mandatory to issue a "Work Permit" which will clearly include the name of the person responsible for checking the condition of the truck and installation, the person responsible for carrying out the shooting work, the operators and which will be signed by each. Each "Work Permit" issued will specify the results of the checks of the truck and the installation, and will be approved by a person appointed in writing by the company's management. • In case the installation travels on public roads to different locations, the truck will have to be certified according to the regulations for road transport. • The personnel serving the installation will be equipped with personal protective equipment and anti-static underwear, certified for working with explosive materials. • The personnel serving the installation will be trained and examined annually regarding the "Working instructions and labor protection measures for the operation of the installation which must be permanently found in the truck cab. • The flexible pipe for the pneumatic transport of the explosive will be of antistatic type according to the norms in force. • Any intervention at the installation with open flame is forbidden, if there is porous granular ammonium azoate in the supply tank. • It is forbidden to operate the installation with defective measuring, control and command devices. • The maintenance of the installation will be performed in accordance with the manufacturer's / manufacturer's recommendations. These records will be kept at the parking place, in a single register paginated, stringed and stamped on each page. This register will be verified monthly by the person appointed in writing by the management of the unit as having attributions regarding the approval of the "Work Permit", which will record under signature the result of the verifications. • The records regarding the quantities of ANFO explosive manufactured and used, will comply with the legislation in force regarding the regime of explosives. • It is forbidden to use the installation without having issued and approved the "Work Permit". • The quantities of raw materials (porous granular ammonium nitrate and diesel) used in the manufacture of a batch as well as the resulting quantity of explosive will be recorded under signature by the person who orders the manufacture of batches of explosive (designated by the management of the unit) and the firecracker with the manufacture / use of the explosive, in a manufacturing report, which will be registered, dated, filed and kept in accordance with the regulations in force regarding the special regime documents. • A copy of the "Certificate of Conformity" in force must be permanently in the cab of the truck. This certificate may be reproduced only in its entirety and without any modification, including the Annex.

Conclusions
The quality of ANFO-type explosives manufactured in the field close to the place of use depends on a number of factors such as the quality of the raw materials (ammonium nitrate and mineral oil), the degree of homogenization which must be as high as possible, the correct dosage close to the composition of which the mixture of fuel and oxidant to react completely. This reaction, if carried out by a mixture of suitable quality, will occur at an explosion rate of more than 2200 -2500 m / s and with a high emission of gases which perform the mechanical work of demolition at a significant pressure. This desideratum is achieved if the adjustment for the quantitative dosage and the homogenization is kept under control, ie the