International Archives of

Oeul Itkmal

Int Arch Occup Environ Hlth 37,193-203 ( 1976)

and E'ilrouiwntal Health © by Springer-Verlag 1976

Simultaneous Exposure to Airborne Flour Particles and Thermal Load as Cause of Respiratory Impairment DUNJA BERITIC-STAHUUAK, F VALIC, MIRA CIGULA, and D BUTKOVIC Andrija Stampar School of Public Health, Zagreb University, Rockefellerova 4, Zagreb, Yugoslavia

Summary

In order to estimate whether only simultaneous exposure to both

airborne flour particles and unfavorable thermal environment alone cause the development of nonspecific respiratory disease or whether sole exposure to flour aerosols is likely to cause impairment of the respiratory system, a group of 80 millers and 130 bakers, all nonsmokers,

Both

were examined

millers and bakers were exposed to approximately the same concentration of airborne flour particles but the latter worked under considerable thermal It was found that between millers and bakers the difference in the preva-

load

lence of respiratory symptoms was not statistically significant

Although

the differences between the mean measured and the mean predicted venti(FVC, FEV 1,

latory function parameters

PEF, MEF 50 %, MEF 75 %) were signifi-

cant both in millers and bakers, they did not differ significantly between This finding suggests that exposure to flour dust may

these two groups

respiratory disease and a re-

cause the development of chronic nonspecific

duction of ventilatory lung capacity irrespective of simultaneous heat load. Respiratory impairment.

Thermal load

Key words: Flour particles

INTRODUCTION

Ramazzini, asthma can of

as

be found flour

in

cation we

the

18th

in

the

form of

l29 l

number

literature describing

bronchial

asthma and

showed

that the

respiratory

lung capacity in

bakers

l 34 l

We

and

in

bakers

fungal flora in found no

genic agents

l4 l

studied the

rhinitis

bakers with

bakers publi-

relationship be-

the prevalence

in

effects

in

flour particles

role of

of

the

and without

chronic

bacterial

of chronic bronchitis

significant difference in

allergic

impairment of ventilatory

Examining the

the development

of publications

In a previous

long-term exposure to symptoms

tween hypersensitivity to flour and

we

A

l 1,6,8,10-16,19-22,27,32,33l

about

bronchitis

described occupational

century,

flour particles

later the

and millers

brings

early as

caused by

frequency of

in

and bakers

patho-

chronic bronchitis.

193

This observation together with the finding that among the bakers, in whose expectorations predominantly pathogenic agents were isolated, there were many without chronic bronchitis, has given ground to the assumption that in bakers' chronic bronchitis it is not infection that plays the most important role l5l Examining a possible direct pharmacodynamic effect of flour particles on the respiratory system we showed the presence of agents that contract smooth muscles l35l. All previous studies of the influence of flour particles on the ventilatory lung capacity and the development of respiratory symptoms have been conducted in bakers Bakers, as a rule, are exposed not only to flour particles but also, simultaneously, to unfavorable thermal conditions It is, therefore, impossible to rule out the additional influence of thermal factors in the development of nonspecific lung disease in bakers In order to assess quantitatively separate contributions of exposure to flour dust and unfavorable thermal environment, we studied two population groups exposed to similar airborne concentrations of flour dust but working under significantly different thermal condition: a group of millers exposed to flour particles under normal thermal conditions and a group of bakers simultaneously exposed to flour particles and to a considerable thermal load.

POPULATION AND METHODS Sample 163 millers and 322 bakers were examined Data on 80 millers and 130 bakers (nonsmokers) were processed in detail in order to exclude the additional effect of smoking on the ventilatory function and the development of respiratory symptoms. The age distribution of the latter was very similar, the mean age of the millers being 37 years, and of the bakers 37 5 years. They differed little in their average length of service (millers: 16 1 years; bakers: 17 5 years). Evaluation of Work Environment

Hexhlet two-stage dust samplers were

used for the sampling of total and respirable particles 38l. Air temperature, humidity, air motion, and radiant heat were measured with standard field instruments Corrected effective temperature (CET) l2l was read and wet bulb globe temperature (WBGT) l38 l and heat stress index by Belding and Hatch (HSI) l3l were calculated. Ventilator Function Pulmonor spirometersl were used for the measurement of the forced vital capacity (FVC) and the forced expiratory volume in the first second (FEV1 ) Five measurements were taken in each subject and the mean of the two highest 1

Jones Medical Instrument Co , 200 Windsor Br , Oakbroak, Ill , USA.

194

values was taken as the result Predicted normal values were calculated using the tables of the European Coal and Steel Community 71 The peak expiratory flow (PEF) was measured using Wright's instrument 2 The predicted normal values were calculated using the prediction equation provided by the manufacturer l31 l For the detection of possible obstructive changes in small airways the maximum expiratory flow-volume curves were recorded in a smaller group of workers on which the maximum expiratory flow at 50% (MEF 50%) and at 75% (MEF 75%) of the control vital capacity were read The flow-volume curves were recorded by means of the flow-volume spirometer3 by Peters et al l28l The predicted normal values were calculated using the equations by Cherniak and Raber l9l. Respiratory symptoms were recorded using the standard British Medical Research Council Questionnaire l24l. Respiratory Symptoms

RESULTS Assessment of Dust Exposure The results of the determination of airborne flour particles in the working environments of the mill and the bakery are presented in Table 1 as cumulative frequencies of concentrations in seven concentration classes (total particles: 0 50 3 99 mg/m 3; respirable particles: 0 50 2 24 mg/m 3 ) The mean concentrations of total particles were 2 02 mg/m 3 and 2 25 mg/m3, and the mean concentrations of respirable particles in the mill and the bakery were 0 88 mg/m 3 and 1 20 mg/m3, respectively. The geometric means for total particles were 2 39 and 1 85 mg/m 3 , and for respirable particles in the mill and the bakery 1.09 and 1 13 mg/m , respectively The exposure levels of millers and bakers were found to be similar.

Evaluation of Thermal Exposure The results of the measurements of thermal factors in the mill and the bakery in two different seasons of the year are presented in Table 2 The level of thermal exposure is expressed as corrected effective temperature, wet bulb globe temperature and as heat stress index by Belding and Hatch Heat accumulation, expressed in kcal/h, was calculated using the expression l18l: A =M+6 6 (tr-35)+ O 6vO 6 (ta-35)-1 2v O 6 (42-pa) where M = energy expenditure (kcal/h); tr = globe temperature (C); 2

Airmed Ltd , Edinburgh, Scotland. Emmerson Comp , Ltd , Cambridge, Ma , USA.

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Table 2 Plant

Thermal environment in mill and bakery Operation

CET (°C)

WBGT (°C)

Heat accumu-

Weighted average

Outdoor air

work load

temperature

lation

(°C)

(kcal/h)

(kcal/h)

HSI

Cool season

Mill

Milling and sieving

147

Packing

157

Dough preparation

172

Bakery

14

16

14 1

-302 2

7 5

12

11 2

-379 9

-19 5

22.5

21 4

-143 1

38 1

24.5

22 8

-654

70.4

22.5

21 6

-190 2

22 7

21

20 7

-253 9

12 3

25.5

24 8

94 4

56 3

27.8

26 6

17 2

91 8

14

Bread baking 165 Warm season

Mill

Bakery

Milling and sieving

147

Packing

157

Dough preparation

172

Bread baking 165

23

23

v = air motion (m/min); ta = air temperature (C); and Pa = partial pressure of water vapor (mm Hg) The mean work load was calculated by weighing the energy expenditures in millers and bakers estimated by Maver and Boras 231 after having analyzed their time distribution between the main work activity, auxiliary activities, and rest Although the energy expenditures during the main activities of the four groups of the examinees were different, the weighted average work load did not differ much because of considerably different distributions of time between the main activity, auxiliary activities, and rest in the four groups of subjects. The time-weighted values of corrected effective temperature, wet bulb globe temperature and the heat stress index were found to be considerably higher in the bakery than in the mill, both in the cool early spring season (mean outdoor temperature 140 C) and the warm summer season (mean outdoor temperature 230 C) The values of WBGT both in the bakery and the mill, were below the threshold WBGT values proposed by the Occupational Safety and Health Standards Advisory Committee on Heat Stress of the U S. Occupational Safety and Health Administration in 1974 l23,30 l,

197

Table 3

Prevalence of respiratory symptoms in millers and bakers Chronic bronchitis

Dyspnea

Wheezing

Nasal catarrh

Millers

15 (18 8%)

22 (27 5%)

15 (18 8%)

27

Bakers

30

(23 0%)

54 (41 5%)

29

X2-test Control

Bronchial asthma

(33 8%)

2 (2 5%)

(22 3%)

39 (30 0%)

4 (3 1%)

O;P>O 05

1 34 ;P>O 05

16 87 ;P< O 01

1 05 ;P>O 05

6.0%

11.0%

4.9%

14.2%

0 03 ;P> O 05 0%

groupa aCited after

l35l.

Table 4 Mean measured and predicted values of FVC, FEV 1, and PEF in millers and bakers, and significance of their difference

Millers N = 80 Bakers

FVC

FEV 1

PEF

Measured Pre P dicted

Measured Pre P dicted

P Measured Pre dicted

4276

5072