Severe visual loss caused by inhalational methanol poisoning in fireworks production: A report on 3 cases.

BACKGROUND
Workers in fireworks production are mainly at risk for explosion injury. However, there are few reports on the consequences of methanol poisoning in fireworks laborers.


CASE PRESENTATION
We report on three patients with visual loss caused by inhalation exposure to high concentrations of methanol, who were engaged in the granulation process of the fireworks manufacturing industry. They presented with severe metabolic acidosis and visual impairments, accompanied by headache, chest tightness, shortness of breath, dizziness, and vomiting. All were diagnosed with acute methanol poisoning. One patient developed bilateral blindness and two patients improved after timely hemodialysis treatment.


CONCLUSIONS
These case reports emphasize the risk of methanol poisoning in the fireworks industry or other factories using commercial alcohol with high methanol content. Early hemodialysis intervention and metabolic acidosis correction are crucial for rescuing visual impairment caused by methanol exposure. Awareness and supervision of commercial alcohol use are indispensable for similar industrial processes.


Background
Fireworks manufacturing in China has nearly ten hundred years history. Occupational injuries are usually hollow organ injuries after explosion including thermal injuries, penetrating injuries due to secondary projectiles and secondary injuries like falls and burns [1] . In the past, no occupational methanol poisoning case was reported in reworks factories, however, recently three workers engaged in granulation process were found severe vision loss after exposure to commercial alcohol containing high concentration of methanol.
Commercial alcohol products are widely used as volatile solvents in many industrial factories. Formic acid, the end product of methanol metabolism, directly inhibit the activity of cytochrome oxidase in mitochondria and interfere with adenosine triphosphate (ATP) production. It results in histotoxic hypoxia that preferentially affects the retina and optic nerve [2] . Methanol intoxication is very dangerous because it can cause metabolic acidosis, severe visual dysfunction, permanent neurological dysfunction, cardiovascular instability and even death. Survivors may develop ophthalmologic abnormalities, dystonia or parkinsonism [3] .
Most cases of methanol poisoning worldwide are caused by the intake of adulterated beverages containing methanol, while occupational methanol poisoning due to inhalation of steam and transdermic absorption is rarely reported [4] . Here, we report three cases of methanol poisoning through respiratory exposure in granulation department in reworks factories.

Case Presentation
Three patients reported acute, painless, bilateral visual loss. The clinical features, biological parameters, clinical treatments and methanol concentration in work environment and commercial alcohol are presented in Table 1. A 48-y-old male was admitted to hospital with blurred vision, chest tightness, vomiting, shortness of breath. He had engaged in reworks granulation work and sprayed adhesive agent into granulating pellet machine by air pump for 8 years. On day 2, his vision deteriorated continuously and could not identify the content of the phone screen. The fundus examination revealed abnormal macular re ex. He was diagnosed with acute methanol poisoning, toxic optic neuropathy and type I respiratory failure. Naked vision of both eyes was 0.06. Fundus examination showed indistinct macular center concave re ection. After the treatment of hemodialysis, short-term glucocorticoids, and other symptomatic treatments, such as acidosis correction, oxygen inhalation, nerve nutrition, vitamin B supplement liver protection, water and electrolyte balance maintenance, his visual acuity had returned to normal (1.0 in the left eye and 0.8 in the right eye) on day 19.

Case 2
A 56-year-old male was admitted to hospital with progressive blurred vision, narrowed visual eld, chest tightness and dizziness. Naked eye vision examination: no light perception in the right eye, and visible only at 30 cm in the left eye. He was diagnosed with acute methanol poisoning, and treated with timely hemodialysis and short-term glucocorticoids. Other treatments according to syndromes, such as acidosis correction, oxygen inhalation, nerve nutrition, vitamin B supplement liver protection, water and electrolyte balance maintenance. His bilateral visual acuity had returned to 0.6 on day 31.

Case 3
A 38 -year-old male was found with severe chest pain chest tightness, shortness of breath, and progressive blurred vision. He had engaged in reworks granulation work for 5 years discontinuously. He couldn't see anything in 10 hours.
Fundus examination showed light re ex disappearance, mydriasis (6 mm), double papillary edema, enlargement of the optic disc cup (C/D 0.75), slightly pale optic disc, fuzzy optic disc boundaries and less thickness of macular fovea. He was treated with glucocorticoids and other symptomatic treatments other than hemodialysis. His eyesight was not improved on day 10 and nally diagnosed with bilateral nerve atrophy and blindness (no light perception) in two months.
Three cases came from three factories with similar scale. The granulation workshop is made with bricks without front door. Polyvinyl chloride resin, strontium carbonate, sulphur and other raw materials mixed in the granulating pellet machine in a certain proportion, then adhesive solvent (industrial alcohol containing methanol) was sprayed into machine by air pump. Each spraying 3-4 seconds, interrupted 2 minutes, continuous stirring 30-60 minutes.
Low-priced "industrial alcohol" (containing high content of methanol) were used as adhesive solvent, and the concentration of methanol in the production environment and in "industrial alcohol" seriously exceeded the government standard (50mg/m 3 and 0.8g/100mL respectively) in Table 1. The working time is 8 to 10 hours per day and 5 to 6 days per week. The average daily use industrial alcohol was around 80-100 kg. The process requires workers to clean machine closely, increasing the methanol intake through the respiratory tract. Their working places is short of ventilation detoxi cation facilities. Workers used anti-dust mask and gloves and did not use anti-poison respirator.

Discussion
Methanol is widely used as a solvent in many industrial, commercial, and consumer products. In current report, 3 occupational workers suffering methanol exposure were presented with acute visual de cits and metabolic acidosis. Respiratory tract of chronic methanol intake cause blindness is a known risk [5] , however, in the past there were no methanol intoxication in reworks manufacturers due to exposure with unquali ed commercial alcohol containing excessive amount of methanol. Three patients are presented with chest tightness, shortness of breath, blurred vision, binocular visual loss hyperuricemia and metabolic acidosis, shortly after high concentration of methanol exposure.
Typical signs and symptoms of acute methanol poisoning include metabolic acidosis, central nervous disorder, and vision abnormality caused by formic acid [6] . Central nervous system damage is often manifested as headache, convulsion, delirium, lethargy, coma, epileptic seizure and coma. Optic nerve damage is manifested as photophobia, double shadow, visual nerve atrophy and irreversible blindness due to progressive demyelination of nerve bers [7] , and patients with severe poisoning show permanent visual impairment [8] . All patients in this paper developed typical clinical symptoms such as vision loss, chest tightness and shortness of breath.
All the patients were treated according treatment principles of acute methanol poisoning, include decreasing poison exposure, metabolic acidosis correction, glucocorticoids, respiratory support treatment, symptomatic treatment and vitamin supplementary. Only Case 3 developed binocular optic nerve atrophy and binocular blindness due to the absence of hemodialysis in early phase.The naked eyesight of case 1 and 2, who were treated with timely hemodialysis, reverted to normal level.
Hemodialysis timely and effectively remove methanol and formic acid, correcting metabolic acidosis and electrolyte disorder, is the most important treatment for acute methanol poisoning [9] . Early acidosis correction and short-term glucocorticoid using are also critical measures to prevent optic atrophy. In our report, symptomatic treatment of drug treatment could not completely block methanol toxicity, while early administration of hemodialysis minimized the severity of visual loss signi cantly. The methanol poisoning accident in workers from granulation departments of reworks factory was, to a large extent, ascribed to lack of management of industrial alcohol purchase, no ventilation detoxi cation facilities, workers' ignorance of risk of methanol and nonuse of anti-poison respirator.