Novokuznetsk State Institute of Postgraduate Medicine,

City Clinical Hospital #1, 

Novokuznetsk, Russia

 

Kuznetsk Basin is one of the largest coal deposits in the world. Kuzbass coal is characterized with its high quality and is related to the best coals. In Kuzbass the total geological coal deposits (at depth of up to 1,800 m) are about 725 billion tons. In 2013 Kuzbass overcame the mark of 200 million, and brought 203 million tons to grass, with increase by 1.5 million tons compared to 2012. The production increase was associated with Yuzhkuzbassugol (+ 1.7 million tons), SUEK-Kuzbass (+ 1.6 million tons), Kusbass Fuel Company (+ 1.4 million tons), Yuzhny Kuzbass Coal Company (+ 1.0 million tons), Raspadskaya Coal Company (+ 0.8 million tons). The amount of the “millionaire teams” is already about twenty in Kuzbass. The labour capacity has been increasing constantly. It was 203 tons per a person in 2011, but 206 in 2012. At the present time 120 enterprises are active at the territory of Kemerovo region. It includes 63 underground mines, 57 open pitch mines and 42 coal conversion plants. The production capacity is 245 million tons for production and 166 million tons for conversion. This industrial field includes 109 thousand people. The working conditions at the Kuzbass mining enterprises are related to the explosion-dangerous production. It is related to high methane levels in coal layers (ejection level is 3-20 m³/min.) from one hand, and periodical critical concentrations of methane-air mixture (in major blowouts), which always exist during technological process of solid fuel extraction [1], from other hand.

Methane explosions and mine fires are about 3.7 % of the total amount of emergent cases, but there are severe group damages in most cases. Methane-air mixture explosion is characterized with the type of vacuum explosion with formation of the specific traumatic factors. The destructive capacity of methane-air mixture explosion is related to both the amount of interacting substrates and the amplitude of combustion product oxidation and characteristics and the volume of air space. One should not believe that excess pressure rate, which is created by explosive wave, acts like the powder charge gases which give kinetic energy for a bullet. At that, victims are thrown by explosive wave to surrounding things and production equipment or are injured with them because of their destruction with explosive wave. The explosion wave strength is so significant that it can cause fall and avalanche in mine workings. It significantly complicates searching and evacuation of victims, but the most important thing is increase of forced isolation in technogenic accident location [2]. For open space the fact is that power and striking force of gas wave decreases by an entity, which is equal to the square of the distance from the explosion epicenter [3, 4]. There is no linear dependence in case of explosion in limited spaces. It creates higher barodeleterious effect of gas wave on the organs in miners who are at the great distance from the epicenter. Furthermore, explosive gas wave include overheated water particles leading in thermal injuries to the open body parts. The explosive wave formation mechanism is related to sudden expansion of gases under high temperature in the fire source. At that, the higher levels of hydrogen create the risk of repetitive, more powerful vacuum explosion, which is possible with additional oxygen and open fire. Together they form the injury factors: explosion wave and increased environment temperature resulting in different physical and mechanical injuries to hearing organs and systems, barotraumas and thermal injuries to air ways, ear and skin [5].

State Committee for Supervision of Industrial and Mining Practices confirmed the safety instructions for all technologic processes and the instructions for different tools and methods of prevention of dangerous factors. However, methane-air mixture explosions and fires after coal self ignition are not removed. It supposes that these rules are not followed to the full extent, or their fulfillment does not permit realization of labour safety [6].

On May, 2011 two significant methane explosions took place in Raspadskaya mine, which is one of the biggest mines in the world. The specialists considered these explosions as the most large-scale in the former Soviet Union. After the first explosion 360 miners were blocked in the mine. Several hours later, the second blast appeared which prevented air ventilation and destructed the part of the land constructions. In the epicenter 91 persons died and went missing. The miners found salvation who had worked distantly.

Objective – to identify the features of the hearing organ damage after explosive mining trauma and to assess the efficiency of the set of measures during long term period.

 

MATERIALS AND METHODS

The work was based on the clinical observations of 141 miners suffered from the explosion of methane-air mixture in Raspadskaya mine (Mezhdurechensk, Kemerovo region) on May, 8-9, 2010. The information about the number of the victims was presented by the enterprise administration. The work is the two-staged analytic investigation. The selection of the patients was performed in concordance with the developed inclusion and exclusion criteria. The inclusion criteria for the first stage of the study (from the explosion till 6 months): all miners who suffered from methane-air mixture explosion in the mining workings, regardless of gender, age, employment history and profession. The study protocol was developed according to Declaration of Helsinki – Ethical Principles for Medical Research Involving Human Subjects, 2000, and the Rules for Clinical Practice in Russian Federation confirmed by the order of the Ministry of Health of Russian Federation, 19.06.2003, #266, with approval from the ethic committee of Novokuznetsk State Institute of Postgraduate Medicine. The included patients signed the informed consent for hearing function examination. The inclusion criteria for the second stage of the study (from 6 months till 3 years) – 126 miners who continued their underground labor. The exclusion criteria for the second stage of the study were 15 injured miners who retired owing to different causes, including health state, after the accident.

The significant proportion of the miners included men – 134 (95 ± 1.8 %). There were 7 women (5 ± 1.8 %). There were 126 labouring men (89.4 ± 2.5 %) and 15 engineers and other technical workers (10.6 ± 2.5 %). The main labor specializations are sinker, winning machine workers, underground electrical fitter, stope miner, underground mine worker. The women worked as manipulator vent unit motorists, fuelers and cagers. The age of the victims varied from 19 to 60. 131 injured miners were the persons at the age of 21-50 (93.2 ± 2.1 %), most qualified and employable. Immediately after the explosions the accident site was visited by mine rescue brigades, teams of Ministry of Emergency Situations, medical ambulance teams and firemen. All victims received emergency aid and were transported to the hospitals of Mezhdurechensk. After the information became available, all nearest clinical hospitals, Scientific Clinical Center of Miners’ Health Protection in Leninsk-Kuznetsky and the clinics in Moscow were ready to admit the injured miners during the first day after the accident. 109 patients needed for long term treatment (78 ± 3.5 %). On the first day the victims were examined by the different specialists. Combined diagnosis was made. Treatment was prescribed with consideration of life-threatening pathology: carbon monoxide poisoning, different injuries, burns, shock states. 32 victims had mild injuries without life threat (22 ± 3.5 %). They received infusion therapy, spasmolytics, analgetics, antihypoxic drugs, hypotensive and sedative drugs, acyzol injections and physiotherapy. The further treatment was realized in outpatient settings, under control of therapeutist, E.N.T. specialist and psychologist. After emergency aid the miners with requirements of longer treatment were distributed between the different departments with consideration of prevailing pathology: traumatology, neurology, orthopaedics, burns unit, pulmonology, cardiology and otorhinolaryngology. Psychologists or, sometimes, psychiatrists took a part in complex treatment of the miners. After general state stabilization the outpatients and hospital patients were directed to surdologist for detailed examination of hearing function, correction of treatment of dominating posttraumatic pathology with consideration of received therapy. In the acute posttraumatic period a significant proportion of complaints was related to the pathology associated with carbon monoxide and combustion product intoxication, head injury (cephalalgia, dizziness, nausea, weakness), upper airway burns, bronchopulmonary pathology (cough, hoarseness, throat irritation, dyspnoea), stress (fear, anxiety, tearfulness, irritation, sleep disorder). The complaints of hearing decrease were presented with presence of its significant pathology (auditary inefficiency of degrees II, II-III, III). The primary investigation showed hearing organ pathology in 106 (75 ± 3.6 %) of the patients including 63 (45 ± 4.1 %) patients with perceptive hearing loss of different degrees, posttraumatic otitis with eardrum rupture in 9 (6.4 ± 2.0 %), hemianacusia in 2 (1.6 ± 1.0 %), thermal burns of ear auricles in 32 (22 ± 3.5 %).

In the acute period of the follow-up or in case of negative dynamics of hearing function the hospital treatment with pharmacological therapy were performed: glucocorticoids (dexamethasone), drugs for improving intravascular microcirculation (rheopolyglukin), vitamins (migamma, vitamin C), antioxidants and antihypoxants (cytochrome C, actovegin), angioprotectors (cavinton), nootropics (piracetam), drugs for tissue metabolism (cerebrolysin), vestibulolytics (betagistin-based drugs). The additional recommendations included hyperbaric oxygenation, acupuncture, cranial electrotherapy stimulation, health resort treatment. 27 miners (19 ± 3.3 %) received the first examination by us only during the annual prophylactic medical investigation (after 6 months), because of severity of their state at the moment of injury and the subsequent stay in other region of Russian Federation (the analysis of discharge summaries was performed). In case of hearing organ pathology identification the treatment with the subsequent audiologic control in surdologist room were performed.

The second stage of examination included observation and treatment during the following 3 years (tonal audiometry, superthreshold audiometry, impedance audiometry, otopharyngeal tube patency examination). The comparison group included 107 persons who were not affected by methane-air mixture explosion, without statistically significant differences in age, work conditions and service length (p = 0.166; p = 1.000). The main occupational hazards in both groups: industrial noise during underground works, general and local vibration, coal dust and changes in temperature of external environment. Entotic sound and speech clarity were not main concerns in the acute period, but the direction changed in the long term period. After removal of life threat the drive to improving quality of life appeared. There was an increasing number of complaints of hearing decrease (from 36 ± 4.0 % to 42 ± 4.1 %). One could observe the increasing rates of speech clarity disorders (from 19 ± 3.3 % to 31 ± 3.8 %), ear and head noise (from 19 ± 3.3 % to 49.9 ± 4.2 %).The significant decreased rates of complaints of head pain, dizziness and throat pathology were observed. Even stress-related complaints decreased to 11.9 ± 2.7 %. During the follow-up the estimation of efficacy of earlier treatment of hearing function was based on subjective estimation of hearing, ear noise dynamics, changes in speech clarity and audiologic examination after treatment over time.

The statistical calculations were performed with Statistica 10.0.1011.0 (StatSoft, Inc., USA, the license agreement # SN AXAAR207P396130FA-0). The statistical significance in view of P value was defined. The null hypothesis was rejected in case of p < 0.05. For qualitative and quantitative signs the frequency response was defined. Z-test was used for identification of differences in the groups.

 

RESULTS AND DISCUSSION

Within 3 years the number of the patients without hearing pathology increased from 24.8 ± 3.8 % to 42.1 ± 4.4 %. Acute tubootitis after acute acoustic barotrauma recovered. In the long term period only 2.4 ± 1.3 % of the miners had chronic salpingitis with mild conductive auditary inefficiency at the background of deviation of nasal septum. Acute posttraumatic perforations of drum membranes (6.4 ± 2.1 %) scarred in view of adhesive otitis and tympanosclerosis without hearing nerve pathology (2.4 ± 1.3 %) and with mild pathology of hearing nerve (3.2 ± 1.5 %). Two miners had persistent perforations at the drum membranes (they rejected from the offered surgery in view of tympanoplasty). The number of the miners with unilateral deafness and mild perceptive hearing loss of the second ear (1.6 ± 1.1 %) did not change. Before the accident the mild degrees of auditary inefficiency were observed in 10 persons according to their medical diagrams (7 ± 2.2 %). In the long term examination the number of the miners with perceptive hearing loss of different degrees was 48.4 ± 4.4 % (table).

Table
Distribution of patients according to degree of sensorineural hearing loss

At the background of treatment the structure of auditary inefficiency degrees changed. The rate of moderate auditary inefficiency decreased slightly from 12.1 ± 4.1 % to 10.3 ± 3.8 %. The rate of primary and mild perceptive hearing loss increased from 24.1 ± 5.4 % till 31.7 ± 5.9 %. The number of the miners with significant perceptive hearing loss increased from 1.4 ± 1.4 % to 6.8 ± 3.2 % with following specialty loss and retirement. The positive moment of the treatment was the fact that the proportion of the patients with mild perceptive hearing loss (11-20 dB of hearing loss for the main speech tokens) increased, but with moderate degree (21-30 dB of hearing loss for the main speech tokens) decreased. The individuals with mild hearing pathology often did not note these changes in their daily communication. But these miners also needed for dynamic follow-up and periodical treatment for hearing function stabilization.

In the control group the hearing pathology was identified in 23 miners (21.3 ± 3.9 %). The greatest proportion of perceptive hearing loss was observed in the age group of 51-60 (14 persons, 13 %). Mild auditary inefficiency (degrees I-II) was observed in 13 miners (12 ± 3.1 %). Audiologic examination showed decrease in hearing in 10 persons (9.3 ± 2.8 %), with similar range (about 5 dB for speech tokens). The control group had more expressed hearing function pathology in the age groups with length of work in harmful conditions of more than 20 years. The comparison group had no cases of rapid decrease in hearing with specialty loss and taking out of the mine. The miners of the control group with decreased hearing received antineuritic therapy one time a year, with non-significant negative dynamics – one time a year and additional vitamin sets during the spring. The special attention was given to associated diseases in both groups with their timely treatment.

In the long term period 57.9 ± 4.4 % of the patients had hearing pathology and decreased quality of life. It is significantly higher than in the comparison group – 21.3 ± 3.9 %. Z-test = 5.325, p = 0.001. Hearing pathology is not only a social problem for them (decrease in social communication level), but it is also associated with specialty, working ability and salary losses.

 

CONCLUSION:

1. Traumatic injuries to hearing organs are 75 ± 3.6 % in miners after explosive mining trauma.

2. Early audiologic examination allows identifying acute posttraumatic perceptive hearing loss, which should be treated as early as possible.

3. Hearing organ damage is not life-threatening at the moment of an injury, but over time it becomes one of the main causes of decreasing quality of life with specialty loss (6 ± 2.1 % in 1.5-2 years), with cost rehabilitation including payments and hearing aid.