Cleaning Of Oil-fired Boilers, Occupational Exposure

allan · May 7, 2007

a From: Roshchin (1968).

4.2.2 Cleaning of oil-fired boilers

Significant occupational exposure to vanadium occurs during

the cleaning of boilers in oil-fired heating and power plants

and ships (Symanski, 1939; Roshchin, 1968; Kuzelova et al.,

1977; Levy et al., 1984). Fuel oil combustion results in the

formation of vanadium-containing dust, and large amounts of dust

result from operations connected with removing ash encrustations

in boiler cleaning and in cleaning the blades of gas turbines.

Most of these operations are carried out by hand, and the dust

in the air inside the boilers may range from 20 to 400 mg/m3,

the most common range being 50 - 100 mg/m3, with the dust

containing 5 - 17% vanadium pentoxide and from 3 to 10% of the

lower vanadium oxides (Roshchin, 1968). Kuzelova et al. (1977)

reported dust concentrations of 136 - 36 036 ml/m3 in the air

with vanadium concentrations ranging between 1.7 and 18.4

mg/m3.

Williams (1952) published air sampling data on boiler-

cleaning operations in the British power industry. He found

concentrations of soot dust at different points ranging from 239

to 659 mg/m3. The vanadium concentrations in the dust of the

superheater chamber was 40.2 mg/m3, while, in the combustion

chamber, the concentration was 58.6 mg/m3. Most (93.6%) of the

dust particles had a diameter of between 0.15 and 1 µm.

8.4 Occupational Exposure

Occupational poisoning occurs mainly during the industrial

production and use of vanadium and in boiler cleaning

operations. Under these conditions, vanadium may enter the

human body through the respiratory tract; an unknown quantity

will be transported to the alimentary tract when swallowed.

Vanadium can also enter through the skin (Roshchin, 1968).

Both acute and chronic poisoning can occur. Vanadium-

containing industrial aerosols differ in chemical and structural

composition and thus evoke different responses in the human

body.

In sections 8.3.1 - 8.3.4, a survey is made of the available

clinical and epidemiological data on the health effects of

vanadium in workers occupationally exposed to vanadium

compounds. Most of the reported clinical symptoms reflect

irritant effects of vanadium on the respiratory tract and eyes.

8.4.2 Cleaning and related operations on oil-fired boilers

Bronchitis and conjunctivitis resulting from exposure to

soot (containing 6 - 11% vanadium) during the cleaning of the

stacks of oil-fired boilers were first recognized by Frost

(1951). Frost did not report any other effects, but, in a

subsequent report of a boiler-cleaning operation by Williams

(1952), sneezing, nasal discharge, lachrymation, sore throat,

and substernal pain occurred within 0.5 - 12 h of exposure.

Within 6 - 24 h, secondary symptoms developed; these consisted

of dry cough, wheezing, laboured breathing, lassitude, and

depression. In some cases, the cough became paroxysmal and

productive. Symptoms lessened only after removal from the

working environment for 3 days. Air sampling showed most of the

dust particles to be smaller than 1 µg. The vanadium concen-

tration ranged from 17.2 mg/m3 in a superheater chamber to

58.6 mg/m3 in a combustion chamber. Roshchin (1962) observed 8

cases of acute vanadium poisoning in workers who cleaned boiler

flues at power stations burning high-sulfur oil. Analysis of

soot deposits showed that the soot in the region of greatest

dust formation (the pipes of the steam superheater and water

economizer) contained from 24 to 40% vanadium pentoxide. The

workers carried out cleaning operations without respirators or

with respirators that did not provide the necessary protection.

After cleaning the boilers, the workers developed acute vanadium

poisoning: itching in the throat, sneezing, cough with difficult

expectoration, and smarting eyes. On the following days, the

symptoms became more severe. Tightness in the chest, sweating,

general weakness, conjunctivitis, and noticeable loss of weight

developed. On examination one week later, hyperaemia and oedema

of the fauces and posterior pharyngeal wall were observed.

Harsh breathing sounds and dry crepitations were heard in the

lungs. X-ray examination showed intensified lung markings in

the middle zones of the right and left lungs and thickening of

the fissure on the right. One month later, only one worker

still had cough, weakness, perspiration, loss of energy, and

dyspnoea. The other workers recovered quickly, with complete

disappearance of cough and shortness of breath.

In another study on workers engaged in boiler-cleaning

operations (Troppens, 1969), the symptoms were described as

similar to mild coryza or influenza with bronchitis. Following

recovery, workers were tired, debilitated, irritable, without

any appetite, and complained of watery eyes. The first symptoms

were swelling of face and eyes as early as 20 min after entering

the boiler area. Removal from exposure for 2 - 3 weeks resulted

in the disappearance of symptoms. Skin blemishes described as

allergic dermatoses were attributed to absorption of vanadium

through sensitive skin. Troppens claimed that there was an

increased susceptibility of the vanadium worker to asthmatic

bronchitis and emphysema.

An investigation is reported on 53 workers performing

emergency repair work on oil-fired power station boilers (Izycki

et al., 1971). They were exposed to vanadium pentoxide in

average concentrations of from 1.2 to 11 mg/m3 and also to

manganese, calcium, and nickel oxides, and sulfur compounds.

Characteristic features of both acute and chronic vanadium

poisoning included upper respiratory catarrh in 45%, increased

lung markings in 24.5%, and bradycardia in 22% of cases.

Persistent chronic changes in the respiratory tract (rhinitis,

pharyngeal catarrh, laryngitis, and changes in the paranasal

sinuses) were present in 45%.

Milby (1974) reported 21 cases of vanadium poisoning in

boilermakers installing new catalytic-converter tubes. This

work involved marble-sized pellets of vanadium containing 11.7%

V2O5. The dust formed during the shaking of these pellets had a

particle size of 1.1 - 1.5 µm. After working for 72 h, the

workers began to complain of nasal, eye, and bronchial

irritation. By the 4th day, most felt very ill, with signs of

irritation of the upper respiratory tract and eyes and pains in

the chest.

In a study by Garlej (1974) 50 workers engaged in the

cleaning of oil-fired boilers were compared with a control group

of 60 other workers. Boiler deposits contained 44 -65% V2O5;

the maximum exposure was estimated to be 10 mg/m3. Although no

clinical evidence of vanadium poisoning was seen, a number of

exposure-dependent positive biochemical reactions were found in

the boiler-cleaning group. Urinary excretion of delta-amino-

levulinic acid (ALA), porphobilinogen (PBG), and porphyrin

increased beyond the physiological limit, and the positive Nadi

reaction (with associated green fluorescence) occurred. The

increased excretion of cytochrome (as indicated by the Nadi

reaction) suggested oxidation through V2O5 of the thiol group

-SH cysteine in the protein carrier, resulting in decreased

binding of cytochrome in the mitochondria.

A study on 17 men who were engaged in cleaning boilers at an

electric generating station was reported by Lees (1980). In

addition to clinical findings, which were similar to those

described above, urine-vanadium levels were determined, and

pulmonary function measurements were made for a week following

exposure. Sixteen of the men wore protective clothing, and

respirators that were found to have about 9% leakage. One

workman volunteered to wear only a simple oro-nasal dust mask

for 1 h of exposure. The dust exposure level was estimated to

be 26 mg/m3; respirable dust (under 10 µm) was measured at

523 µg/m3 with a vanadium content of 15.3%. All of the men

developed reduced pulmonary function that had not fully returned

to normal in one week, but did so after one month. Reduced

function outlasted the clinical symptoms by several days. Fig. 3

shows the contrast in pulmonary reaction between the more

heavily exposed individual and one of the other workmen. The

urine-vanadium level of the volunteer was 280 µg/litre, whereas

those of the remainder of the workers were below 40 µg/litre.

Other observations of boiler-cleaning operations have been

made by Fallentin & Frost (1954), Sjöberg (1955), Thomas &

Stiebris (1956), Hickling (1958), and Kuzelova et al. (1975).

In terms of respiratory symptoms relating to boiler-cleaning, it

should be noted that sulfates and sulfuric acid may be present

in boiler soot and may be partly responsible for irritative

effects. Hudson (1964) suggested that the quick onset of

symptoms (lachrymation with nose and throat irritation) with

rapid recovery following removal from exposure is character-

istic of exposure to acid sulfates. Response to vanadium expo-

sure is characterized by some delay in the onset of irritative

symptoms (a few hours to several days) and persistence of

symptoms following removal from exposure (Hudson, 1964).

A recent report by Levy et al. (1984) concerned a

comparatively high incidence of severe respiratory tract

irritation in boilermakers (74/100), many of them welders in

areas without adequate ventilation, exposed to vanadium

pentoxide fumes in a power plant where conversion from oil- to

coal-burning occurred. The severe illness of 70 men caused an

average of 5 days of absence, some objective tests (e.g., FVC)

being markedly affected. The vanadium pentoxide content was

above the permissible exposure limit in 8 samples, and this

resulted in litigation for inadequate protection of the

workers.

Kuzelova et al. (1977) drew attention to the occupational

risk of chimney sweeps cleaning large-capacity heating

facilities in large housing settlements. This coincided with a

report of a detailed cross-sectional examination of 121 chimney

sweeps by Holzhauer & Schaller (1977) in the Federal Republic of

Germany with an average exposure duration of 19 years ( ± 5

years). Vanadium exposure was determined by personal samples,

and measurements between 0.73 and 13.7 mg vanadium pentoxide/day

were determined compared with 4 µg in the normal (average)

population. Urinary excretion was determined to be between 0.15

and 13 µg/litre, which was significantly higher than the values

in 31 referents. The main complaints of the chimney sweeps were

wheezing, rhinitis, conjunctival irritation, cough, sputum

dyspnoea, and hoarseness; there were no skin symptoms. A

prospective follow-up of the cohort was emphasized, but the

results are not yet available.

Hoppy · May 7, 2007

Allan,

It is interesting that you made this post today. Last night I heard really loud noises caused by steam venting from a power plant that is on a Marine Corp. base near here. I looked over at the base and saw about 20 fire trucks surrounding the base. I figured that there had to be some nasty chemicals going in the air so I got out of town.