The analysis of the reasons of explosions of tank truck at loading

In result the new reasons of explosions which were not considered in cases when tank trucks are poured with diesel fuel earlier have been revealed, but before they are transported gasoline and vice verse. Besides process of absorption of vapour of gasoline by diesel fuel and, connected with it, occurrence of explosive concentration of vapour of gasoline is revealed during tank truck filling , and also - influence of internal designs of the boiler of a tank truck on process of occurrence of the spark category of static electricity.

All oil products (gasoline, diesel fuel) concern to liquid dielectric (their specific resistance is 1011..1013 Оhm*m). It means, that at movement on pipelines, as a result of friction between layers and separate particles under laws of physics, there is an electric potential which is formed owing to loss of electrons on the top environments of atoms or ions in long chains of molecules. This process goes in two directions: electrization and relaxation that is restoration. Layers of a liquid which are on small distances from a wall of pipelines easily relax and, finally, in the pipeline of sufficient length a certain average cumulative charge which is characterized by a parameter " volumetric density of electric charge " is formed and (Coulomb/m3) is measured in physical units.

Coulomb - quantity of the electric charges which are taking place through section of a conductor at force of current in 1A for 1 sec.

The size of volumetric density of the charges, oil product moving on a pipe, depends on many factors (speed, presence of impurity, including waters, temperatures, viscosity, structure, etc.). Serially made devices for gauging size of volumetric density are absent.

The product, with the electrostatic potential got in a pipe, acts in the boiler of tank truck at an output from a bulk pipe in open space (having poured a falling jet) and is in part unloaded through a metal environment of an earthed tank truck. The product also in part gets an additional charge in result of spray (divisions into separate fine particles) and gets in the places located on some distance from walls of the boiler of the tank. Despite of rough hashing during receipt of new quantity of a product, any small time in the certain volume can arise high enough size of volumetric density of electrostatic charges, and accordingly - the high electric potential reaching 3..5 kV concerning walls or acting metalwork (bundles, angles, the cores located in parallel or with an inclination to "mirror" of a product.) Physically connected to the boiler of the tank. During this moment probably occurrence of the spark category with capacity sufficient for ignition of explosive concentration of oil products which in the certain conditions resulted below, can arise in the boiler of the tank truck at performance of operation of loading.

At existing theories of occurrence of static electricity as experimenters admit, practical results of the formed volumetric density of electric charges can differ from settlement in 10 times in both directions. Therefore process of formation of electrostatic charges at loading of tank trucks, and also occurrence electric spark or crown categories, now is not controllable and to affect it is impossible. With a small degree of reliability it is possible to assert and adhere to the following obligatory conditions:

• Loading by open jet should be excluded ( loading pipe should be in contact to a bottom of the tank);
• Speed offloading during the initial moment should be no more than 1..1,2 m/sec (time of loading on the given speed should be enough that the mirror of a product has hidden completely target windows of loading tip);
• Presence in the boiler of the tank of any acting designs, beams or the rods located in parallel or with an inclination to a mirror of a product is inadmissible;
• External grounding of tank truck is necessary with the help of the device supervising size of resistance of transitive contact of ticks of grounding with a metal part of the boiler of the tank.

Occurrence of explosion is provided with concurrence of 2 events:

• Presence at present explosive concentration of the mixture of vapour of oil product in volume, sufficient for development of explosion.
• Occurrence in the given volume of the spark category of necessary capacity.

Let's consider conditions of occurrence of explosive concentration of vapours of oil product at loading of tank truck.
1. According to law of Dalton " the Sum парциальных pressure of components of a gas mix is equal to the general{common} pressure of a mix of gases the given volume ". In our case in the boiler of the tank at наливе the general{common} pressure of a mix паров mineral oil and air equally to atmospheric pressure. Temperature of a mix also close to an ambient temperature, however structure and concentration паров, arising at наливе gasoline and diesel fuel, naturally different.

Gasolines of various grades have pressure sated паров on Spot-check in a range from 500 mm рт. An item (years{summer}) up to 650 mm рт. An item (winter). The given sizes are measured at 38°С and indirectly define{determine} ability to borrow{occupy} a corresponding share at formation{education} of steam-air mix (ПВС) due to evaporation. The size of this share, to be exact volumetric concentration, also depends on an ambient temperature. As have shown хроматографические researches - the structure of components of the steam-air environment includes the following hydrocarbons: prosir, изобутан, н-butane, пентан, н-пентан, гексан, and volumetric their concentration in 1 m3 ПВС depending on temperature can be in limits from 15 % at temperatures -30°С up to 55 % at temperatures +30°С.

It is necessary to pay attention, that explosive concentration паров gasolines makes from 2 up to 6 volumetric interests. Having applied these conclusions to process налива tankers gasoline, we shall receive the following results:
- If the tank till the moment налива transported gasoline at plum on walls and pipelines the rests of a product which easy hydrocarbons evaporating in a range of the mentioned above temperatures always create concentration паров above 15 % take place. Receipt of a new share of gasoline (during the rough beginning налива) can raise{increase} only concentration available there паров easy hydrocarbons (ЛУВ).

Hence, occurrence of explosive concentration паров in this case inside the tank is impossible. The first condition (event) for occurrence of explosion is absent. Occurrence of the spark category at presence ПВС with concentration паров ЛУВ is higher than 6 % - explosion inside the boiler does not provoke in all a range of temperatures and during all time налива.

But! The steam-air mix (ПВС) superseded from a tanker at наливе with enough high concentration ЛУВ, gets in environmental external space. By virtue of what densities ПВС of gasoline (2? 4 kg / m3) are higher than densities of air (1,2 kg / m³), last falls to space around of a tanker and installations налива, and concentration of her{it} sharply decreases also probability of its{her} decrease{reduction} to a limit of explosive concentration becomes rather high. Therefore the probability of occurrence of the spark category around of installation and tankers should be excluded.

It is necessary to undertake the following actions:

• To apply closed having poured tankers (bottom or top) at which the bulk tip has герметизирующий a cone and газоотводящий the pipeline on which 90-95 % ПВС are allocated{removed} on safe from installation and a tanker distance,
• The clothes and footwear of the attendants should be antistatic,
• The automobile should be technically serviceable, the engine заглушен, work of any electrodevice is excluded, ignition is switched off, electroposting is serviceable,
• The tools used at work, should have a covering excluding искрообразование at contact or impact with metal or earthed parts of installation and tankers,
• The electric equipment of installation should be executed in explosion-proof execution{performance}.

Diesel fuel (years{summer}, winter) has pressure sated паров 10-13 mm рт. An item on Spot-check at temperature 38°С. The given size shows, that испаряемость this product very low and volumetric quantity{amount} ЛУВ in ПВС паров diesel fuel with air at any temperature less than 1 %, that is practically explosive concentration at наливе, plum and transportation of diesel fuel inside the tank if gasoline or others ЛУВ there is not mixed, does not arise.

Hence, at operations with diesel fuel if in a tanker there was a diesel fuel, there are no conditions of occurrence of explosive concentration ЛУВ as inside the tank, and outside.

However, at research of processes of recycling паров ЛУВ rather good ability of diesel fuel to absorb in itself pairs (бутанов, пентанов, гексанов, etc.) is revealed. It is experimentally established, that from one m3 ПВС with concentration of 40-50 % on the advanced surface of contact ЛУВ and a film of diesel fuel of it{him} it is enough for absorption ЛУВ 25-30 л.

It shows, that at наливе tankers in which before gasoline was transported, diesel fuel take place the following events:

• Till the moment налива concentration паров ЛУВ inside the tank was higher some diesel fuel explosive,
• After the beginning of receipt in this tank of diesel fuel ЛУВ from ПВС are quickly absorbed by diesel fuel, concentration of them decreases and becomes fast explosive. And at reduction of concentration ЛУВ from ПВС - speed of their absorption (абсорбирования) decreases, therefore on an extent practically all time налива tankers inside it{her} concentration паров ЛУВ in ПВС is in limits from 2 up to 6 %.

As it was described earlier, probability of occurrence of the spark category during all time налива rather high. It is necessary to note, that inside a tanker always except for two above named conditions there is 3 condition is a necessary volume in which explosive process of fast burning is capable to develop, thus there is a pressure about 10кг/sm² and temperature about 2500-3000°К. Capacity of explosion in " a trotyl equivalent " is defined{determined} by weight ЛУВ which is taking place at this time in a suspension, i.e. at free volume 5м3 at concentration ЛУВ of 5 %, having assumed, that in reaction 20 % of active substance will take part only, explosion which capacity it is equivalent 100г тринитротолуола turns out. As a rule, such explosion is accompanied by destruction of the boiler of the tank, ignition of the spread diesel fuel and drawing of traumas to the attendants, sometimes with a fatal outcome.

Conclusion - to strictly forbid having poured diesel fuel in the tank in which before there was a gasoline without special preparation.

Having poured gasoline in the tank in which there was a diesel fuel earlier. Valid before stated, explosive concentration паров arises only in an initial stage налива which is necessary for making with safe speed 1-1,2 м/сек during time necessary for full closing of an exhaust outlet of a bulk pipe.

P.S. Installations (complexes measuring) such as АСН, Open Societies " Промприбор " let out{released} now, completely meet the requirements of explosion safety at realization of process налива a tanker.

However, from the maintaining organizations precise performance of organizational actions is required:

• Survey (certification) of park of tankers with which it is necessary to fill with mineral oil for absence inside the boiler various металлоконструкций and technical serviceability
• Недопущение presence inside boilers of various subjects (empty capacities, etc.)
• Instructing and training of drivers of gasoline tank trucks for observance of conditions of explosion safety at наливе
• A categorical interdiction налива in the tank of diesel fuel after transportation in it{her} of gasoline without the special preparation providing 100 % removal{distance} паров of gasoline
• Observance of the schedule of change of productivity налива:
  • The small charge 1-1,2 м/сек which time of action is programmed at commissioning,
  • The nominal charge, which size is selected and programmed at commissioning from a condition of absence of hydroimpacts, and also influence of height взлива a product in the account tank,
  • The minimal charge at the end of the set doze which time of action is programmed at commissioning
• The periodic control of size of grounding, installation over than 4 Ohm, sizes of resistance between the end of a bulk pipe and an installation site заземляющего a conductor - no more than 10 Ohm. Sizes of resistance of transitive contact of ticks of the grounding fixed on a tanker and an electric circuit of the control of this contact - no more than 100 Ohms, and also operation of the device of grounding of a tanker on switching-off налива at infringement of contact of ticks with a tanker. Periodicity of the control is established proceeding from climatic conditions, rate налива on a place by a management{manual} responsible{crucial} for operation.
• The clothes and footwear of operators налива, making installation of a strut with a bulk tip, should be antistatic
• The presence{finding} of operators on a tanker during time налива is inadmissible. The most safe place can be on a platform of installation, but it is better on the ground near to established button " STOP ".