Evaluation of the strain induced by a change in the work organization of a refractory brick molding process

Introduction
A new organization of the production of refractory bricks proposed to mould 4 bricks instead of 3 during cast periods which are thus increased from 10-12 to 14-16 minutes. Seven to 9 cast periods separated by about 40 minutes rests were possible by shift. Bricks are very large pieces molded at 1800 °C in moulds manually dismantled by 2 workers. During the cast, heat stress is characterized by very high radiant heat and wearing of heavy aluminized protective equipment. Our objective was to quantify the strain of the new work organization.

Methods
The 6 workers involved in the task volonteered. Heart rate (HR) was recorded continuously. After each cast the workers assessed subjectively the physical (Borg RPE) and thermal (0=comfortable to 4=intolerable) strains. For the purpose of the study workers achieved casts of 2, 3 or 4 bricks during their shift.

Results
The peak HR cost measured at each brick (n = 134), is on average of 73.8 (et=10.0) bpm. The mean strains are high during the casts of more than 2 bricks. But subjective (RPE=15.5, se=0.6) and cardiac (HR = 128.2 bpm, se=3.3) mean strains are not different in casts of 3 or 4 bricks (p>0.3). If rests are taken in the air conditioned rest room, HR returns to its basal levels during each rest after casts with either 3 or 4 bricks.

Discussion
The results show that the transition from 3 to 4 bricks per cast does not increase significantly the heat and metabolic strain. The new organization is then possible without adding risks if attention is given to effective periods of rest and cast duration. At last, the good agreement between measured and subjective data shows that the last ones give as essential information to convince as measured data.