Opinion by
Porter, J.,The plaintiff brings this action against his employer, the defendant, to recover for injuries sustained in the course of his employment, alleged to have resulted from the negligence of the latter. The injury occurred from the bursting of a pipe fitting, which was part of an air compressor system. There was, under the evidence, no doubt that the plaintiff was injured while in the course of his employment, but the circumstances were such as to require the plaintiff to prove that the accident resulted from the negligence of his employer and that such negligence was the cause of the injury.
The negligence alleged was in continuing to use an air compressor system with a defective auxiliary valve, which ought to have regulated the pressure to which the receiving tank, pipes and fittings were subjected. There was evidence that the valve was defective, that this was a source of danger, that this was known to the man to whom the employer had given control of this particular branch of the business, that the facts had been communicated to the superintendent of the factory, that a new valve had been ordered, but that the operation of the compressor, with the valve in this dangerous condition, had been continued for a considerable period. Two witnesses had testified that the failure of the valve to operate properly caused the tank, pipes and fittings to be subjected to a high pressure, caused the air to become hot and vaporized the oil contained in the pipes and tank, which uniting with the air would form a gas and that this would ignite and explode, and that, in their opinion, the accident was caused by an explosion within the pipe. One of these witnesses was the man employed by the defendant to operate the compressor, he was present when the accident occurred and said that he saw fire issue from the pipe when the fitting gave way, and that “If the new valve had. been put on the explosion would not have occurred, at least I do not think so.” The qualifications of this witness as an expert are not *133questioned by any assignment- of error, and he had been employed by this defendant as an expert and had charge of the machinery which caused the accident. The other witness, Britton, had been in the employ of the defendant as a machinist for several years, had worked about this air compressor and had particularly observed the alleged defective valve, while he had not had a technical education he did have practical experience with machinery of this character, peculiar knowledge upon the subject which cannot be assumed to be possessed by the ordinary man. Whether either of these witnesses was really a scientific expert, whose opinion should be relied on, whether their reasons for considering the use of - the machinery dangerous were consistent with each other, and whether either really showed that the explosion was in fair probability caused by the defective valve, are questions on which we may entertain doubts, but they were questions of fact for the determination of the jury. In the face of this positive testimony, the court could not have assumed that the injury did not result from the alleged cause: Walbert v. Trexler, 156 Pa. 112; Stevenson v. Coal Company, 203 Pa. 316; Follansbee v. Garrett-Cromwell Engineering Co., 48 Pa. Superior Ct. 183. This disposes of the second, fourth, eighth and ninth specifications of error.
There was no exception taken in the court below to the admission of testimony embraced by the first specification of error, which is for that reason dismissed. The sixth and seventh specifications of error relate to the action of the court in sustaining objections to certain questions asked the witnesses by counsel for the defendant. These specifications are without merit as the defendant was permitted, under questions in another form, to introduce the testimony of the same witnesses as to all the material facts sought to be developed by the questions.
The plaintiff had called Emory Bender, who testified that he was present at the time of the accident and gave *134the details of the occurrence. He was then examined by the • plaintiff as an expert and stated that, in his opinion, the breaking of the fitting was caused by the auxiliary valve not working properly, which caused the unloading valve not to work properly, and too constant working of the machine would probably heat it; “If it would heat it high enough I thought that would cause the air and the oil in the pipe in the receiving tank to ignite and explode.” The defendant proposed to ask this witness on cross-examination whether it was not more probable that the break in the fitting was caused by a .latent defect therein, and whether, in the absence of such latent defect, any break in the system, caused by high pressure or an explosion, would not have occurred at some other part, rather than at the fitting, which was naturally capable of resisting higher pressure than the other parts of the system. The plaintiff objected to this question and the court sustained that objection, saying: “Is not this asking for an opinion without laying a foundation for it?” The court seems to have inadvertently overlooked the fact that this witness was being cross-examined, his competency as an expert had already been passed upon by the court, the plaintiff had offered him as an expert witness and as an expert witness he had given an opinion favorable to the plaintiff. The defendant had the right in cross-examination to' ask him any material question directly bearing upon his testimony-in-chief as to what caused the accident. The third specification of error is sustained.
The theory upon which the plaintiff presented his case was that the high pressure of the air, caused by the defective valve, generated heat, which vaporized the oil, which combining with the air exploded at a high temperature. Each of the two witnesses called to sustain this contention stated that if the heat got high enough it would “ignite the oil and explode.” They made these statements in answer to direct questions by the counsel of the plaintiff. The theory of the defendant was that *135the accident was caused by a latent defect in the pipe' fitting which gave way, that in the absence of such defect the fittings were the strongest part of the whole system, and that no explosion had occurred inside of the pipes. The defendant called as a witness Jacob D. Aldinger, to whose competency as an expert the plaintiff made no objection, and who was certainly by training and experience qualified to give an expert opinion. This was the only witness in the case who made any attempt to distinguish between an explosion, in the technical sense, and the bursting of a pipe from internal pressure, such as some times occurs in the pipes and fittings of water mains. He defined an explosion, in the sense in which it was used in the present case, as the sudden burning of oil vapors mingled with the- compressed air, thus immediately developing an extraordinarily high pressure. The defendant proposed to prove by this witness that no explosion could have taken place within the compressed air tank or pipes, in the manner testified to by the witnesses for the plaintiff, namely: by a combination of air and oil; that an explosion could only take place, within a compressor operated as this one was, through ignition by a spark, and that it was altogether improbable that any spark could reach the point at which the explosion was alleged to have occurred. The introduction of this evidence was objected to and the court sustained the objection, saying: “There is no evidence in the case of an explosion caused by ignition by a spark anywhere in the plaintiff’s case, or by any witness on the stand.” The learned judge, in the hurry of the trial, evidently forgot that the witnesses upon whose testimony the plaintiff relied had said that the combination of vaporized oil and the air would “ignite” and explode. We are of opinion that it was competent for the defendant to prove that, under the conditions here presented, a combination of compressed áir and vaporized oil would not explode in the absence of a spark, and that it was improbable that any spark could have reached the point *136where the explosion is alleged to have occurred: Alexander v. Water Co., 201 Pa. 252. We are, therefore, constrained to sustain the fifth specification of error. With the exception of these rulings upon the admission of evidence the case was well tried by the learned judge of the court below and was submitted to the jury in a charge of which the defendant had no cause for complaint.
The judgment is reversed and a new venire awarded.