Opinion by

Mr. Justice Elkin,

If the combustion, or explosion, or whatever it was that caused the accident, resulted from sparks emitted from the defective and unguarded motor in the fustic room, *436this case was for the jury on the question of negligence. This was the theory upon which the case was tried and as we understand the contention of appellant it is not denied that if the explosion was occasioned by the emission of sparks from the motor, the jury might infer negligence for which appellant would be answerable in damages. The contention is earnestly made that the evidence is not sufficient to warrant an inference that the explosion was occasioned by the emission of sparks from the motor in the fustic room, and that the probable cause of the accident was left to mere conjecture. It is suggested that the unfortunate occurrence was the result of dnforeseen conditions which could not have been anticipated and for which no one is responsible. If the injuries for which damages are sought to be recovered resulted from causes beyond the control of appellant, or if the explosion was accidental and without fault on the part of anyone, or if latent and dangerous agencies, unknown to appellant and so unusual as not to be anticipated in the exercise of ordinary business judgment, caused the injuries complained of, there could be no recovery on the ground of negligence. The duty of a master does not require that he protect his servant against all dangers or casualties. He is bound to furnish a reasonably safe place to work and reasonably safe tools or appliances with which to work. The standard or measure of safety depends upon the kind and character of work done. Some kinds of work are more dangerous than others and some tools and machinery are more complicated and necessarily involve more risk than other kinds. These varying conditions must always be taken into account in determining the measure of safety required in such cases. As a general rule a manufacturer meets the requirements of the law when he furnishes the kind of tools or appliances in general use in the particular line of manufacture in which he is engaged. If these were the only questions involved in the present case we would unhesitatingly say that the place as well as the tools and appliances in general use in the manufacturing estab*437lishment were reasonably safe within the meaning of the law. But these are not the only questions, and it becomes our duty to give further consideration to the facts in order to determine the legal rights of the parties. The evidence shows that a motor, necessary to the manufacturing process, was placed in the fustic room several feet above the floor and near the wall of the building. This motor was neither covered nor guarded. For several weeks prior to the accident it had been emitting sparks at frequent intervals and of varying sizes. Some of the witnesses testified that these sparks frequently had the appearance of a flame two or three inches long. The fustic room in which the motor was located was filled with wood dust while the plant was in operation. This wood dust settled on the floor two or three inches deep and covered the walls, ceiling and entire interior of the room. Employees working there tied handkerchiefs over their mouths and noses in order to protect themselves against this cloud of wood dust, which at times was so dense as to limit the range of vision to a few feet. These were the conditions in the room in which the motor was constantly emitting sparks, or as some of the witnesses called them, flames of fire. The motor had been emitting these sparks for several weeks before the accident occurred. There was some evidence tending to show that the motor was defective and that this defective condition caused the emission of the sparks, especially those described by the witnesses as flames. It is contended for appellant that a motor in first-class condition will emit sparks and that there was nothing so unusual in the present case as to put it on notice of anticipated danger from this cause, certainly not that an explosion might result therefrom. It may be conceded that appellant was not bound to anticipate what did actually occur. If such an occurrence had been anticipated, the instincts of humanity and self-interest would have suggested that steps be taken to guard against consequences so appalling. The case in our opinion does not turn upon what knowledge the appellant had, or did not have, as to *438the explosive character of wood dust. It does not require expert knowledge to inform a person with ordinary intelligence that a spark or flame two or three inches long may and sometimes will ignite wood dust. This is within the common knowledge of every person. As an illustration take the conditions in the fustic room as shown by the evidence, the average man, master or servant, would say at once that it was dangerous to have sparks or flames frequently thrown out into such an atmosphere. The danger from fire at least would seem to be apparent even if an explosion had not been anticipated. We think the danger was sufficiently apparent to put the employer on notice and that steps should have been taken to protect the employees against that danger. A little care and very slight expense would have averted the danger and saved an innocent employee in another part of the building and whose duties did not require him to have any knowledge of the conditions in the fustic room, from the grievous injuries suffered. It is true, as is contended for appellant, that a servant is not entitled to have his case submitted to the jury, unless he introduces, in addition to the fact of the happening of the accident, testimony which fairly tends to show negligence on the part of the employer. In the absence of such additional testimony, save in those exceptional cases in which the doctrine of res ipsa loquitur applies, an action for damages is not maintainable: Labatt on Master and Servant, sec. 835. It is perhaps unnecessary to remark that the doctrine of res ipsa loquitur has no application under the facts of the present case. In this case the burden was on appellee to prove substantive facts from which the inference of negligence might be fairly drawn, and in our opinion the proofs submitted were sufficient for this purpose. The testimony of the eyewitness, Moore, who was standing in the fustic room at the time of the accident, and who saw and heard what occurred in connection with the motor, if believed by the jury, as it evidently was, fully warranted the inference that the trouble originated in and around the motor. He *439describes where he was and what he saw and did at the time of the accident. He testified among other things, that, “I was up there [meaning in the fustic room] about a minute before the explosion. Time enough to stoop down and open up the hole in the floor. I heard a racket and the motor slow up, she went right off in my face.” He accounted for the accident by saying that the motor exploded, and when asked what he meant by saying the motor exploded, he replied, “Flames of fire shot in my face, and knocked me out.”

He also testified that immediately after seeing the flash of fire from the motor, “the brick wall partition between the redwood department and the fustic department blew out.” He further testified that the brick wall partition between the two rooms was blown away from the fustic room and toward the redwood room. The only inference to be drawn from these facts is that the explosion occurred in the fustic room, and that the trouble originated in and about the motor. The emission of sparks, or flames of fire, would account for all that happened. We cannot agree that the testimony of the witness, DeShields, who was also on the fifth floor of the building but in another department, contradicts Moore. Indeed, as we read the testimony of these witnesses, one corroborates the other in all essential particulars. Certainly there is no greater variance as to the details of the accident than would be expected in the testimony of two witnesses subsequently relating what took place at the time of this most unusual occurrence. But even if different inferences might be drawn from their testimony it was the duty of the jury to draw them. DeShields testified, among other things, “I heard this noise, and I whirls around and goes toward the steps [meaning the stairway leading from the fifth down to the fourth floor] and I heard the noise again, and when I heard the noise I seen something like electricity and in the meantime the whole thing just lit up and I started to run down the stairs; and I got down about halfway of the steps and so I don’t remember getting down on *440the floor, but I soon recovered; when I found myself I was on the floor, and I gets up from there then and made a dash toward the big door and was going to jump out the fourth story window.” These were the only witnesses on the fifth floor at the time of the accident. The one was in the fustic room and saw and heard what occurred there, the other was in another department separated by a wall, but it was possible for DeShields to see all he says he saw through the open stairway which in a way connected the two departments. Their testimony warranted the jury in finding that the explosion occurred on the fifth floor in the fustic room, and the only reasonable inference from all the facts is that the sparks, or flames so called, emitted from the motor, were the proximate cause of the explosion. Under these circumstances it would have been error to have withdrawn the case from the jury.

The third assignment raises a different question. It is contended that the learned court below committed reversible error in using figures by way of illustration in the computation of damages. Benson v. Railway Company, 228 Pa. 290, is relied on to sustain this contention of appellant. That case is not authority for the position taken here. It was there pointed out that the use of figures by way of illustration in charging a jury as to a method of ascertaining the present value of loss of future earnings is a dangerous practice, but such use of figures is not ground for reversal, if the judge instructs the jury that he is only using the figures by way of illustration, and that he did not intend to indicate what he thought the verdict should be. The judgment in that case was affirmed although practically the same question was raised there as here. As we review this record no harm was done appellant by use, of the illustration about which complaint is now made. Indeed, the effort of the trial judge was to impress upon the jury the important fact in the consideration of such cases, that the present worth of future earnings should be their guiding -thought in arriving at a proper verdict. All of which tended to protect appellant *441and was not in disregard of its rights. The learned counsel for appellant must have been impressed with this view of the situation at the time of the trial because no points were submitted nor requests made for more definite instructions on this branch of the case. We are not convinced that any harm was done appellant by the instruction complained of and do not feel warranted under all the circumstances in reversing the judgment on this ground.

Assignments of error overruled and judgment affirmed.