Unintentional Carbon Monoxide Poisoning Outbreak from 2 to 9 October 2019 in Ulaanbaatar, Mongolia


Carbon monoxide poisoning (COP) from 2 to 9 October 2019 was a major public health concern in Ulaanbaatar, Mongolia, after a transition from consumption of raw coal to upgraded briquette fuel. During the period, a total of 186 residents, which is 16 times more than the previous years, were exposed to COP and 6 persons died at home. We conduct a cross-sectional study by using registration data and medical history of all hospitalized patients with a diagnosis of COP from 2 to 9 October 2019 and had an in-depth interview. 144 (77.4%) people from 85 households registered as potential cases and 124 (86.1%) people were diagnosed with COP. All households used upgraded briquettes, and 41 households (48.2%) used them for the first time. In 50% of cases, the stove was broken, the chimney was short, not heated, and the clay joint connecting the wall stove was broken. The majority of interviewees were unaware of COP and improperly used briquettes, and the safety of chimneys and stoves was insufficient which caused unintentional COP. It is necessary to provide information to the local population about the potential risks of COP, install CO alarms in households, and educate the population. In further, a well-established poisoning surveillance system is an important aspect of public health emergency preparedness in Mongolia.

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Otgonbyamba, O. , Altangerel, E. , Ganbat, G. , Ganbold, B. , Sodnomjamts, A. , Chuluunbaatar, B. , Badrakh, B. and Batbaatar, S. (2023) Unintentional Carbon Monoxide Poisoning Outbreak from 2 to 9 October 2019 in Ulaanbaatar, Mongolia. Occupational Diseases and Environmental Medicine, 11, 97-114. doi: 10.4236/odem.2023.112006.

1. Introduction

Carbon monoxide (CO) is a colorless, odorless, non-irritant gas, which is present in our environment naturally (40%) or artificially as a result of human activities (60%), and vast amounts of CO are released into the atmosphere by burning fossil fuels (car exhaust emissions, burning natural gas, forest fires, etc.) [1] [2] . It is known as a “silent killer” because it causes more deaths from poisoning than any other toxic agent which is inhaled during the incomplete combustion of coal and other hydrocarbon products [3] . About 95% of the absorbed CO readily binds to Hb to form carboxyhemoglobin (COHb) because Hb’s affinity for CO is more than 200 times greater than for oxygen. Thus, the percentage of total blood Hb in the form of COHb is a biomarker of CO exposure [4] . Most cases of carbon monoxide poisoning can be prevented by improper combustion in buildings and homes [5] . The main sources of carbon monoxide exposure in the home are faulty, poorly sealed, or ventilated home heating systems, stove chimneys, kitchen appliances, car exhaust, and gasoline or other fuel-burning equipment (e.g., stoves, portable generators, space heaters) [6] .

COP is one of the most common fatal poisonings in many countries in the world [7] . Korea began using improved (compressed coal) fuel (Yongtang) for winter cooking and heating in urban areas in the mid-1950s, and the improved briquette was used three times. In Taiwan, from 1997 to 2003, a significant increase from 1.6 - 3.5/10 person-years was found in the rate of unintentional deaths from COP induced by inappropriately ventilated gas heating appliances (54.3%), fires, and automobile exhaust fumes (7.4%) [8] . Effective public health interventions to reduce morbidity and mortality associated with outdoor and indoor air pollution include moving away from raw coal and solid fuels, switching to cleaner fuels, and potentially boosting a country’s economy [9] [10] [11] .

Ulaanbaatar, Mongolia is considered the coldest capital city in the world [12] , with a temperature frequently falling below –20˚C in wintertime. A considerable part of households there live in gers, traditional Mongolian dwellings made-up of a wooden frame beneath several layers of wool felt, which are not connected to centralized infrastructure such as heating and water supply [13] . In the ger areas of Ulaanbaatar, cooking and heating energy is provided through indoor coal combustion in metal stoves with chimneys, and in such cold wintertime, such stoves may be used both day and night. Air pollutants emitted from various sources are trapped in a temperature-inversion layer above the city [14] . In Ulaanbaatar, 80% of air pollution source is due to the burning of coal, briquette fuel, and food in household stoves and ~3200 heat-only boilers in the ger area [15] . Thus, the air pollution associated with burning coal has negative impacts on public health and is a risk that continues to be a serious public health problem [16] [17] [18] [19] . To address health and environmental concerns, the Government of Mongolia has shown considerable efforts to reduce air pollution in Ulaanbaatar. One of them is banning the consumption of raw coal and replacing it with high-quality briquette fuel. The fuel is produced according to the Mongolian standard “Upgraded solid fuel. Technical requirements” MNS 5679: 2022 [20] . Starting in the winter of 2019-2020, the consumption of raw coal was banned for household consumption in Ulaanbaatar according to the Governmental decision [21] [22] [23] .

To address health and environmental concerns, the Government of Mongolia has shown considerable efforts to reduce air pollution in Ulaanbaatar. One of them is banning the consumption of raw coal and replacing it with upgraded briquette fuel. In 2016-2019, before the briquette has been consumed in Ulaanbaatar, 198 to 243 people suffered from COP. Since the implementation of the briquette fuel, the number of COP cases was notably increased and been reported. According to data from the National Emergency Center for Poisoning, Mongolia, from 2 to 9 October 2019, a total of 186 people were exposed to COP, and 20 were hospitalized, 6 died. A 15-year-old girl was hospitalized in an unconscious state after COP. Even though the patient’s condition improved and she came to consciousness, brain tissue is not capable of regeneration, and necrosis of nerve cells occurred. She is under the observation of medical specialists in the hospital until other system organs are stabilized not still discharged from the hospital (as of 15 December 2022).

However, the implications for CO exposure are still uncertain. An experimental study compared the CO levels between households using briquette fuel versus those using raw coal and CO levels were significantly lower in cases with briquette fuel [24] . The current study aims to define the causes of the outbreak of carbon monoxide poisoning in Ulaanbaatar, Mongolia.

2. Materials and Methods

2.1. Participants and Study Design

This is a cross-sectional study conducted using quantitative and qualitative survey methods. For the quantitative part of the study, we used registration data and medical history of all hospitalized patients with a diagnosis of COP (T58 according to ICD-X) [25] and concomitant symptoms who visited the National Emergency Center for Poisoning, Emergency Department of the National Center for Maternal and Child Health, and Capital Emergency Department from 2 to 9 October 2019 in Ulaanbaatar. The study also included patients undergoing oxygen therapy who experienced syncope, headache, dizziness, vomiting, nausea, and palpitation based on differential diagnosis according to the standard MNS6449: 2014 “Diagnosis and treatment of acute carbon monoxide poisoning”. Due to no approved national case definition for diagnosing COP in Mongolia, we used the case definition of US CDC [24] guidelines and ICD-X [25] classification. To narrow the inclusion criteria for the study, the cases were divided into the following 4 categories:

- Presumable: COP from burning solid fuel + loss of consciousness or death.

- Probable Diagnosis: Suspicion of nausea, headache, vomiting, dyspnoea, chest pain, and vital signs oximetry or epidemiological link to confirmed cases.

- Confirmed Diagnosis: Probable Diagnosis + Determination of carboxyhemoglobin in peripheral blood by laboratory tests (COHb 2.5% in non-smokers, >7.0% in smokers).

- Death: The death which is confirmed by on-site examination by police, hospital, court, and the conclusion of the General Agency for Specialized Inspection in association with household COP due to burning of briquette fuel.

Cases of COP related to occupational poisoning, intentional poisoning, other diagnoses of gas poisoning, or exposure to the fire were excluded from this study.

The survey was conducted with a pre-designed questionnaire which consists of 39 questions to clarify the causes and circumstances of poisoning. The questionnaire includes information on the social and demographic status of the household, the type of apartment and stove, the frequency of burning, the amount of fuel in a single fire, fuel ignition time, and the first symptoms. Adult members of the household and caregivers exposed to CO and adults who were during the lighting fire were interviewed by telephone.

2.2. Field Evaluation and Qualitative Survey

Quantitative data were collected from 14 households, of which 20 hospitalized patients and 6 dead belong, by conducting an in-depth interview with hospitalized residents, visiting their homes, determining the condition of stoves and chimneys used, the amount of fuel used at a time, and documenting them with photographs. The in-depth interviews were conducted via face-to-face meetings as well as via telephone due to emerging situations.

2.3. Data Analysis

The qualitative data, and the collected data were processed using the classification methodology. After this, set-offs were developed according to evaluation guidelines and all interviews were coded. Analysis was done using an explanation approach based on common and specific factors of coding. Qualitative data were used in the evaluation report as references.

The quantitative data were analyzed by using SPSS-23 software. The results are expressed as a percentage and mean of the variables of the study population. According to Kolmogorov-Smirnov test all data was not normally distributed thus estimates (prevalence) and frequency intake, age, and values of vital parameters (SPO2, PO2, PCO2) of patients were elaborated by the median and interquartile range, 95% CI and percentage. The mean CO exposure time was calculated as a difference between the time of the last firepot and the time of onset of symptoms. Differences between variables were calculated by chi-square, and correlations between variables were calculated.

3. Results

3.1. General Information of Patients

3.1.1. Review of COP in 2016-2019 in Ulaanbaatar

Table 1 shows the number of people exposed to poisoning and COP in 2016-2019 in Ulaanbaatar. Statistics are taken from the National Emergency Center for Poisoning, Mongolia. In Ulaanbaatar, in 2016-2018, 198 - 243 cases of COP were recorded per year, that is, 0.01 - 0.31 cases per 10,000 population and the mortality was 3 - 6. From January to September 2019, 402 cases were registered, or on average 44.6 ± 4.3 [95% CI: 49.6 - 65.5] cases per month, and 11.2 ± 5.1 [95% CI: 10.9 - 14.5] cases per week. 1 victim died in 9 months. However, in the period from 2 to 9 October 2019, in Ulaanbaatar, a total of 186 residents, or 16 times more, were exposed to carbon monoxide poisoning over 8 days, and 6 citizens died at home.

3.1.2. Descriptive Statistics

According to outpatient registration, during the survey period, 186 cases were admitted with the pre-diagnosis of COP in 6 districts of Ulaanbaatar. Of these, 144 (77.4%) persons from 85 households registered as potential cases and interviewed by phone, 124 (86.1%) people were diagnosed with COP (T58 in the ICD-X) Emergency department of the district health center 20 (13.8%) people were admitted to the hospital, no confirmed cases were registered due to the lack of treatment and laboratory diagnostics. According to the forensic medical examination and the Police Department official report, 6 (3.2%) from 5 households died at home as a result of an accidental COP. The mortality rate was 0.04%. Of 122 (84.7%) citizens, symptoms of the disease were registered in the hospital emergency list, 75 (52.1%) had vital signs, 72 (50.0%) were smokers, 35 (24.3%) were non-smokers, the remaining 37 (25.7%) were not marked, the type of apartment and information about the stove is not recorded, and 109 (75.7%) contact by telephones of persons were marked (Figure 1).

According to the survey result, all surveyed households used upgraded briquette fuel for heating and cooking purposes, 41 households (48.2%) used the fuel for the first time, 21 households (14.6%) for the second time, and 23 (28.2%) households used it longer than past 4 days. 56 (65.8%) households lived in dwellings with fireplaces and 40 (47.05%) households had simple traditional stoves. Among 144 cases contacted by telephone, 80 (55.6%) were women with a median age of 27 [95% CI: 24.9 - 31.3], and 9 (11.2%) were pregnant. The youngest age of acute COP was an infant (10-day-old), and the oldest was an 89-year-old man. The mean age of dead adults was 40 years old (the oldest was 62 years old and the youngest was 28 years of age), the youngest was 2 years old, 4 (66.7%) men and 2 (33.3%) women (Table 2). The patient’s symptoms are directly related to the severity of the condition (r = 0.5, p = 0.0001).

The stove type used by the household (x2 = 53.6, p = 0.0001) and the chimney cleaning behavior (x2 = 11.5, p = 0.003) have statistically significant differences. However, the use of an upgraded briquette was not statistically significant (Table 3).

The volume of one-time household consumption of upgraded briquettes has a direct correlation with the stove type (r = 0.26, p = 0.018) and the frequency of fuel consumption (r = 0.24, p = 0.025).

Table 1. Number of people exposed to poisoning and COP, 2016-2019. Source: National Emergency Center for Poisoning, Mongolia.

Figure 1. General statistics of COP cases from 2 to 9 October 2019 in Ulaanbaatar.

Table 2. Demographic characteristics of COP cases, 2-9 October 2019.

Table 3. Stove types, cleaning, and burning behavior in the households exposed to COP from 2 to 9 October 2019.

3.1.3. Medical Care and Clinical Symptoms

In this study, presenting time and clinical symptoms of registered patients from 2 to 9 October 2019 are analyzed. Presenting time was registered for 121 out of 144 patients. Most (51 or 42.1% of registered patients) of the patients were presented between 00:00 and 06:00 hours following 45 (37.2%) between 18:00-24:00 hours, 17 (or 14%) and 8 (or 6.6%) were presented between 6:00 and 12:00 hours and between 12:00 and 18:00 hours, respectively. A total of 28 (19.4%) cases were classified as mild, 64 (44.4%) as moderate, 20 (13.8%) as severe and 17 (22.2%) as more severe, but 15 (10.4%) cases were not registered. 101 (70.1%) cases received oxygen therapy.

Out of 144 total cases, 126 (87.5%) cases had 2 - 3 symptoms such as headache, dizziness, vomiting, nausea, and fainting, while 18 (12.5%) had no symptoms (Figure 2). Vital parameters were determined in 82 (56.9%) patients, the median level of SPO2 was 91.7 ± 7.2 [95% CI: 88.7 - 91.6] %, PO2 was 44.2 ± 18.8 [95% CI: 45.3 - 50.5] and PCO2 was 36.8 ± 6.2 [95% CI: 37.1 - 40.9]. For severe

Figure 2. Symptoms recorded in the hospital emergency form, Ulaanbaatar city, 2-9 October 2019.

and more severe patients, the median SPO2 was 85.3 ± 7.1 [95% CI: 82.4 - 87.3], PO2 was 44.1 ± 7 [95% CI: 41.9 - 48.9], and the PCO2 was 33.5 ± 8.6 [95% CI: 34.1 - 41.4], while the median SPO2 was 92.0 ± 3.0 [95% CI: 91.4, 93.6], the median PO2 was 51.4 ± 24.6 [95% CI: 45.3 - 54.5], and the median PCO2 was 37.2 ± 4.5 [95% CI, 37.4 - 43.7], for mild to moderate severity patients.

For moderate patients, the median level of SPO2 was 95.5 ± 5.2 [95% CI: 93.7 - 96.8], PO2 was 48.3 ± 20 [95% CI: 41.7 - 54.5], and PCO2 was 38.1 ± 3.0 [95% CI: 36.7 - 38.1].

Out of 20 (13.8%) hospitalized cases, 14 (16.5%) were under the supervision of family doctors, and out of 5 (5.8%) households and 6 died. At admission, 17 (85%) had a severe course, 3 (15%) had a more severe course, and 9 (45%) had a loss of consciousness, lethargy, vomiting, or convulsions. On median, symptoms appeared 2.9 ± 0.9 [95% CI: 1.8 - 4.2] hours after burning the briquette fuel, and the length of stay in the hospital was 27.4 - 67.2 hours.

3.2. Qualitative Research Results

The field assessment included 14 households, 5 (35.7%) of them used wall stoves with simple traditional stoves, 4 (28.5%) used secondhand improved stoves, 4 (28.5%) used traditional stoves, and 1 (7.1%) used heat-only-boiler. The stoves were operated in the households for 6.3 ± 4.1 [95% CI: 4.1 - 5.7] years in average and 35.0 ± 34.6 [95% CI: 38.7 - 54.2] briquette pieces or 3.7 - 6.4 kg of upgraded briquette were used in stoves per single firing. 9 (64.3%) households used upgraded briquette for the first time, and 5 (35.7%) used it for more than 2 days. In 50% of cases, the stove mouths were broken, the chimney was short, and not heated, and the clay joint connecting the wall stove was broken (Figure 3). After the COP, the families improved their stove and chimney safety by sealing the stove chimneys and cleaning the chimneys (Figure 4).

Most cases affected by COP did not follow instructions on how to use the fuel, however, the instructions were provided on the fuel bag and the fuel was eligible for all types of stoves. In addition, it was informed that they closed the chimney valves to keep them warm longer. The majority of interviewed respondents stated they were unaware of COP and fired the upgraded fuel as usual as raw-coal burning. However, people who use raw coal said that they open their windows and doors and open their chimneys only when there is a smell of smoke. Most households started to burn a fire between 7 and 10 a.m. and added some more fire during the day, and most households cook on the fire. Households with low insulation add fire 3 - 4 times a day on average, and it has been observed that adding coal is done in a way that does not involve a certain amount.

The majority of households surveyed mentioned that they sweep chimneys once every 7 - 14 days, but no sweeps were made during the survey observation. However, based on observations done by interviewers it was revealed that the

Figure 3. Poor pipe sealing chimneys and stoves in households affected by COP in Ulaanbaatar from 2 to 9 October 2019.

Figure 4. Re-sealing in chimneys and stoves in households affected by COP in Ulaanbaatar from 2 to 9 October 2019.

majority of households do not sweep chimneys and stoves for a long time, and stoves and chimneys were found poorly sealed, and firing people overfilled their stoves with upgraded briquette fuel. 10 interviewees of household members exposed to COP clarified that most parents or those at home most commonly light a fire.

4. Discussion

The present survey defined the first major outbreak of acute carbon monoxide poisoning that occurred in Mongolia due to household use of upgraded goal. It has been defined that there is a risk if the population is not provided with accurate information and guidance on fuel use.

Worldwide, the COP and mortality caused by COP have risen in many countries where the burning of fossil fuels becomes a source of CO emission. In the US, Japan, France, and England, CO exposure is increased by power outages during natural disasters such as hurricanes, sea storms, earthquakes, and floods [5] [26] [27] [28] . According to epidemiological studies, during autumn (October-November) and winter (December-January) temperature changes or on rainy and snowy days, COP occurs when coal, briquettes, kerosene, and gas fuel are burned in damaged and unrepaired stoves, chimneys, and open stoves, increases due to ignition of the gas generator [26] [29] - [36] .

Incidents of COP in the 1960s in Korea due to Yongtang briquette, deaths increased dramatically, and it is currently the country with the highest number of deaths from coal briquettes in the world [37] . There was a huge epidemic of COP in the 1970s and 1980s in Korea. In addition, it was noted that there is a need to inform the public and clarify surveillance activities [37] .

Introduced by Mattiuzzi et al. [38] , the incidence of COP does not differ between sexes, whilst mortality is double in men. The incidence shows two apparent peaks, between 0 - 14 years and 20 - 39 years. The percentage of patients who died constantly increases in parallel with aging, peaking in patients aged 80 years or older. The number of COP grows in parallel with the socio-demographic index (SDI), though more detailed analyses would be needed to confirm our findings. Mortality displays a similar trend, being approximately 2.1- and 3.6-fold higher in middle and middle-to-high than in low-to-middle SDI.

COP significantly increases the burden on the emergency department, researchers have noted the need to provide the population with preventive knowledge, take into account language and cultural differences, and improve data recording for less developed countries [39] [40] [41] . It has been recommended that clinicians and professionals be trained in the diagnosis of COP, case-based surveillance, emergency preparedness, and the use of CO-oximeters in diagnosis [24] [26] [41] [42] . In the US, the highest rates of hospitalization for CO were reported in the 0 - 17 and 18 - 44 age groups, and although women presented more frequently than men, men were more likely to be hospitalized and those hospitalized were over 85 years of age [43] [44] . Taiwan has the highest level of CO exposure in children, and the main sources are space heating systems (54.3%), fuel combustion in unventilated stoves (28.4%), and smoke (7.4%) [8] . According to conducted cohort study in China, children aged 15 - 19 have the highest rates of poisoning, and large-scale information campaigns are recommended [45] . Although the incidence of COP does not differ by sex, the death rate among men is twice as high. When considering cases by age groups above 0 - 14 years and 20 - 39 years but mortality is higher in people over 80 years of age. Mortality rates follow the same trend but are 3.6 times higher in countries with higher GDPs than in middle and developing countries [38] .

In addition to the survey for major COP cases that occurred from 2 to 9 October 2019, we have collected further information on COP cases until 31 March 2020. 2768 people from 837 households were exposed to CO poisoning. Of the total number of registered cases, 10 cases were related to alcoholism, and 2 cases were rejected due to complications of other diseases. A total of 2756 cases were diagnosed as gas poisoning and 56.3% (1450) of people who received health care service due to COP were women and it was no statistically significant differences between women and men (x2 = 13.7, p = 0.45). The mean age of the victims was 23.0 ± 19.5, 50.7% of them were children aged 0 - 17 years. These results were similar to above-mentioned survey results. It was shown that the preventive measures for protecting children are required to take in a well-organized manner. To mention, shifting to upgraded briquette usage is one of the short- and mid-term measures for reducing air pollution.

While, observation of our study, emergency centers were overwhelmed during poisonings and medical facilities were unprepared. In particular, there was no CO-oximetric equipment for determining carboxyhemoglobin in peripheral blood, and diagnosis and treatment were carried out based on history and symptoms. The public health response is not ready. For example, there were no approved recommendations and guidelines for case definitions to be used in surveillance, experts were not trained, and records were unclear. This points to the need to improve surveillance, response planning, and hospital preparedness.

The impact of fuel types on indoor air quality was studied by Enkhjargal et al. [46] . Indoor air quality was found to be affected by fuel, dwelling type, and stove type, and households using improved stoves and briquettes were found to be better than households using traditional stoves and raw coal users. The findings of the current survey were also similar to this survey result. Also, according to our survey findings, the main factors that cause acute COP are a family, 2 - 3 hours after lighting a fire. Acute COP in young children occurred at home due to incomplete combustion of coal or heat-only boilers, and in 85.1% of cases one family member was exposed to radiation, and three or more members were affected. Among those poisoned (68.8%), no measures to prevent CO leakage when using stoves and heat-only boilers were taken, in addition, there was a lack of proper and safe use of stoves and heat-only boilers, closing the stove valve to reduce coal consumption at night. Similar conditions which resulted in acute COP were revealed in households in Ankara where the stoves and heaters were used improperly and most of the families had not taken precautions before poisoning [47] . The families used stoves and water heaters improperly and unsafely and ventilation holes of the stoves were closed down during sleep to reduce fuel combustion at night. This resulted in COP of more than one person in a family as family members share the same room.

5. Conclusion

Unintentional cases of COP registered from 2 to 9 October 2019 were studied in detail using surveys and field observation. In half of the COP cases, indications of COP factors were inadequate usage of briquette fuel and unsafe conditions of stoves and chimneys, and insufficient awareness of COP. In order to prevent COP, there is, therefore, a need to inform and educate the population on the safe manner usage of firing, maintaining their stoves and chimneys, and extensive use of CO alarms in each household via using the different channels of mass media. In addition, a well-established poisoning surveillance system is a vital aspect of public health emergency preparedness in Mongolia and changes in fuel consumption into cleaner fuel.

6. Limitations

This study has certain limitations. The main sources of data collection were emergency medical cards and surveys of poisoned patients. Two-thirds of all patients reported to healthcare facilities within 72 hours, resulting in an increased workload and poor record keeping. For example, the lack of vital signs of patients, the lack of pulse CO-oximeters in emergency rooms, the absence of laboratory diagnostics, etc. However, we identified the conditions and epidemiological relationship of poisonings by conducting interviews.

Because the study did not include a reference population to compare with the exposed group, we were unable to assess the risk of this study population compared to the general population. In addition, since we cannot determine the CO concentration during exposure, we cannot comment on the uptake and kinetics of CO by the body.

Author Contributions

Conceptualization, methodology, formal analysis, writing—original draft preparation, O.O.; validation, formal analysis, data curation, E.A.; writing—review and editing, G.G.; investigation, B.G.; writing—original draft preparation, data curation, software, A.S.; supervision, B.Ch.; writing—review and editing, B.B.; supervision, writing—review and project administration, S.B. All authors have read and agreed to the published version of the manuscript.


We would like to thank the investigators at the National Emergency Center for Poisoning, the National Center for Maternal and Child Health, the Emergency medical service center of Ulaanbaatar city, the United Nations Children’s Fund (Mongolia), and the National Center for Public Health for their collaboration. The third author was partly supported by the Shanghai B&R Joint Laboratory Project (grant number 22230750300).

Informed Consent Statement

Ethical permission was obtained from the Ethical and Research Committee at the MOH on February 04, 2020, by resolution #02.

Conflicts of Interest

The authors declare no conflicts of interest regarding the publication of this paper.


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