The opinion
DUFRESNE, Chief Justice
(dissenting).
Petitioner Towle, for two previous years during the period from April to October, had operated a power broom or street sweeper, without suffering any incapacitating accident. True, when interviewed by Dr. Thomas Martin, Jr. in connection with his physical disablement of April 13, 1972, Towle related that he had experienced shoulder and back pains during the last month (September) of the 1971 seasonal operation of the sweeper, but daily massages had kept the pain under control and, following his shift to his winter duties, the malaise had disappeared. When he resumed work on the sweeper in late March of 1972, however, he began having similar symptoms of pain between his shoulder *75 blades and mid dorsal region, which progressed to an acute stage on April 13, 1972, the pain being so severe that he had to discontinue his work.
The medical evidence diagnosed petitioner’s disability as due to a postural strain. The record supports the fact that, in order to guide the sweeper for a proper performance of the work to be done, Towle had to assume a certain posture on the vehicle, and this positioning, combined with the steady bounce to which, as the operator of such a sweeper, he was subjected, together with the direct blowing of cold spring air down his neck and back from a blower installed in the cab for ventilating purposes and to keep the dust out, served in the instant case to cause the back strain which totally incapacitated Towle for work on April 13, 1972.
The Commissioner found that
“[n\o specific incident caused this condition.” (Emphasis added.)
In denying compensation, he explained his decision in the following terms:
“In a Petition for Award of Compensation, the law requires a claimant to establish an accidental injury arising out of and in the course of employment before benefits may attach. These requirements are not in the alternative and each must be established.
“In the instant case, the condition most probably arose out of and in the course of Mr. Towle’s employment as a sweeper operator. However, we are unable to find that the condition resulted from accidental injury and must therefore dismiss this pending Petition.”
Thus, the Commissioner’s ruling concedes that Towle’s personal injury arose out of and in the course of his employment, but it denies recovery of benefits under our Workmen’s Compensation Act on the ground that nothing in the evidence points to a specific occurrence, however slight, supporting an accidental injury, such as a greater than usual jolting on any given day or at any particular time, or some unusual lurch or other untoward event. His holding may be viewed, as the Court of Appeal of Louisiana, First Circuit, in Hargrave v. Travelers Insurance Company, 1966, La.App., 187 So.2d 8 , saw it:
“[Wjhere symptoms of disability gradually appear, increasing imperceptibly until ultimate incapacity results, unless the legal requirement [of a specific incident] of an accident, however slight, is met, the condition must be deemed a noncompensable occupational disease, unless, of course, the condition falls within the category of occupational disease expressly designated by the statute as com-pensable.”
I disagree with such an interpretation of our Act.
The Legislature did not define for us what it intended by the use of the words “personal injury by accident” as used in the context of 39 M.R.S.A. § 51. In Patrick v. Ham, 1921, 119 Me. 510 , 111 A. 912 , this Court reviewed the different definitions of the term “accident” given by several lexicographers. It did not establish as a prerequisite for the existence of a personal injury by accident that there be proof of a specific event to which the injury or death be attributable. In fact, it cited with approval the case of Hughes v. Clover & Clayton & Co., 1909, 2 K.B. 798, quoting from it as follows:
“A workman, whilst tightening a nut with a spanner, fell back on his head and died. A post-mortem examination showed that there was a large aneurism in the aorta, and that death was caused by a rupture of the aorta. The aneurism was in such an advanced condition that it might have burst while the man was asleep, and a very slight exertion or strain would have been sufficient to bring about a rupture. The trial judge found that the death was caused by a strain arising out of the ordinary work *76 of the deceased operating upon a condition of body which was such as to render the strain fatal, and held that it was an accident within the meaning of the law. This decision was upheld both by the court of appeal and the House of Lords.”
In construing “injury by accident” similarly as the English Court had construed its Act in Hughes v. Clover & Clayton & Co., supra, the Court stated:
“That Patrick was suffering from diseased arteries pre-disposing him to cerebral hemorrhage is of no consequence in the case. That he might have died, or would have died in his bed, of cerebral hemorrhage, in a year or a week is immaterial.
The question before the Commission was whether the work that he was doing on the afternoon of October 13th, 1919, caused the cerebral hemorrhage to then occur. If so, we think it was an accident arising out of and in the course of his employment.”
I must conclude that an “accident” in the legislative sense is an “unlooked for mishap or an untoward event which is not expected or designed,” and where the body succumbs to strain or exertion arising from the performance of one’s normal employment, i. e., where something goes wrong within the human frame itself, even though the strain or exertion be the result of the ordinary stresses of the employment, there is a personal injury by accident arising out of the employment when the required exertion becomes too great for the person doing the work, whatever may be the degree of exertion used. See, Ciuba v. Irvington Varnish & Insulator Co., 1958, 27 N.J. 127 , 141 A.2d 761 .
In Moores v. Structural Concrete Corp. of Maine, 1969, Me., 255 A.2d 892 , the employee, while doing his usual work of lifting and carrying bags of cement, felt a back pain. He favored his back the rest of the day, and, even though he stayed away from work the next day, his back kept getting worse. Reporting for work after three days, he managed to stay on the job for two or three weeks by leaving early every day because of his back pain. Thereafter, “my back started bothering again” to the extent that he was unable to work. The Court concluded that the evidence permitted no reasonable inference other than that the employee suffered an injury by accident.
In Moores , the Court was dealing with a case in which the original pain came upon the employee while he was doing his regular work without the occurrence of any outside unusual event. Although disabling for the first few days, the pain did not, however, prevent Moores from resuming his employment, and it was only some two to three weeks later, when the pain had gotten progressively worse, that he was unable to continue working. The Court went on to say that, notwithstanding the physician did not tell with certainy the internal condition of the employee and his prognosis was not free from question, nevertheless, the proof was certain and sure that there was injury internally and, since this is so, there was an injury by accident.
In the instant case, the proof was definite, and so concluded the Commissioner, that there was internal injury suffered in the performance of the usual duties of the petitioner’s employment from the very beginning in March, 1972. True, it was not disabling at first, but the strain which Towle suffered in his back became progressively worse as it continued to be aggravated by his employment to the extent that within at most five or six weeks his internal injury had become totally disabling.
The injury was received while the employee was doing the work for which he was employed, and, in addition thereto, his injury was a natural incident to the work. To be compensable an injury must be one of the risks connected with the employment, flowing therefrom as a natural con *77 sequence, and directly connected with the work. Gooch’s Case, 1929, 128 Me. 86 , 145 A. 737 .
Even if the strain did not arise out of an unusual, undesigned, unexpected or sudden external occurrence in the course of the employment, nevertheless, the ensuing disabling injury would necessarily be an accidental one under the law, because of the unusual, undesigned, unexpected or sudden results of the strain. Mamie Taylor’s Case, 1928, 127 Me. 207 , 142 A. 730 . The initial strain in this case was itself sudden, unusual, and unexpected as these terms are used in Workmen’s Compensation cases and constituted a personal injury by accident, even though the same may not have been compensable for lack of disablement. When the strain incapacitated the employee within a short time from its first occurrence by reason of its progressive aggravation due to the effect of the employment upon the weakened internal structural resistance of his body, the accidental injury became compensable.
An internal injury that is itself sudden, unusual, and unexpected is none the less accidental because its external cause is a part of the victim’s ordinary work. Moores, supra; Mamie Taylor’s Case, supra; Brown’s Case, 1924, 123 Me. 424 , 123 A. 421 , 60 A.L.R. 1293 .
In the recent case of Matthews v. R. T. Allen & Sons, Inc., Me., 1970, 266 A.2d 240 , we said:
“The Workmen’s Compensation Law represents a relatively recent concept of responsibility without negligence. While the early cases usually concerned accidental injuries where an external force was applied to an external portion of the body, our own Court decided early in the development of our law that the term injury by accident includes incidents where internal parts of the physical structure break down under external force, including the stress of labor. While this may more dramatically occur as a result of a slip, a fall or a single unusual strained effort, we have found other such internal breakdowns to have resulted from the usual work which the workman was performing in his usual, normal way.” (Emphasis supplied.)
In Matthews , after reexamining the holding of this Court in McNiff v. Town of Old Orchard Beach, 1942, 138 Me. 335 , 25 A.2d 493 , we stated:
“We do not construe this opinion to be a holding that the Petitioner had to satisfy the Commissioner that the injury was suffered at a particular moment while throwing up a particular shovelful of dirt or to hold that a weakness in the bodily structure which has gradually worsened and which breaks down finally from the stress of usual work may not be termed an injury by accident.” (Emphasis mine.)
In Matthews , we reaffirmed the holdings of Hull’s Case, 1925, 125 Me. 135 , 131 A. 391 , and Swett’s Case, 1926, 125 Me. 389 , 134 A. 200 , to the effect that “if stress of labor aggravates or accelerates the development of a preexisting infirmity causing an internal breakdown of that part of the structure a personal injury by accident occurs.”
Towle’s initial sprain, which occurred after he resumed in March of 1972 his seasonal operation of the sweeper, ensued in consequence of his doing his usual work in a usual manner. It may be said to be a matter of common knowledge that the operation of heavy motorized equipment which ordinarily results in no ill effect may on occasion produce a strain or sprain of the muscles or ligaments of the operator. When the injury is shown to be related to or to have been effected by the employment, that is to say, if but for the employment the injury would not have occurred, the statutory prerequisites of an accidental injury have been met. The mere absence of an extraordinary effort, strain, or exertion, on the part of an employee in his employment does not necessarily foreclose his sustaining a personal injury by accident arising out of and in the course of *78 his employment pursuant to 39 M.R.S.A. § 51. Ciocca v. National Sugar Refining Co. of New Jersey, 1940, 124 N.J.L. 329 , 12 A.2d 130 .
In Bernier v. Coca-Cola Bottling Plants, Inc., 1969, Me., 250 A.2d 820 , this Court quoted with approval the statement in Larson’s Workmen’s Compensation Law § 12.20 to the effect that
“Preexisting * * * infirmity of the employee [such as a weak back] does not disqualify a claim under the ‘arising out of employment’ requirement if the employment aggravated, or combined with the * * * infirmity to produce the * * * disability for which compensation is sought.”
Thus, the stirring into activity of a dormant condition of weakness of a person’s back by a strain incident to that person’s work constitutes a compensable accident.
The policy of our Workmen’s Compensation Act is to protect the employee against risks which are created by and incidental to the employment. Brown v. Palmer Construction Company, Inc., 1972, Me., 295 A.2d 263 . In order to carry out the manifest and general humanitarian purpose of the Act, a broad and liberal interpretation of its provisions is mandated as against a hy-pertechnical construction which can only lead to a frustration of the ends of such legislation. Estabrook v. Steward Read Co., 1930, 129 Me. 178 , 151 A. 141 ; Harry Scott’s Case, 1918, 117 Me. 436 , 104 A. 794 .
As Professor Larson says, “by accident” is now deemed satisfied in most jurisdictions “either if the cause was of an accidental character or if the effect was the unexpected result of routine performance of the claimant’s duties,” and accordingly, “if the strain of claimant’s usual exertions causes collapse from heart weakness, bach weakness, hernia and the like, the injury is held accidental.” (Emphasis supplied.) Larson, Workmen’s Compensation Law, §§ 38.10, 38.20, 38.30.
Where the stress of labor induces or aggravates an internal strain or breakdown, there is a personal injury by accident, whether the physical disablement is the result of cumulative employment exertions or the effect of a single incident. Towle’s disability was clearly an unintended consequence of the employment. The statutory term “accident”, if liberally construed, will encompass a disabling sprain which is conceded to be causally related to the employment, even though no specific incident of the work can be pointed out as the particular onset of the injury. See, Jones v. California Packing Corp., 1952, 121 Utah 612 , 244 P.2d 640 ; Ortiz v. Ortiz & Torres Dri-Wall Company, 1972, 83 N.M. 452 , 493 P.2d 418 ; Hudson v. Owens, 1969, Ky., 439 S.W.2d 565 ; McIver v. State Highway Commission, 1967, 198 Kan. 678 , 426 P.2d 118 ; Lewis v. Department of Law Enforcement, 1957, 79 Idaho 40 , 311 P.2d 976 ; “An accidental injury within the meaning of the Workmen’s Compensation Act need not be attributable to one particular event, but may arise progressively from the cumulative effect of a series of exertion episodes.” H. J. Jeffries Truck Line v. Grisham, 1964, Okl., 397 P.2d 637 ; Farmers Co-Op Exchange of Weatherford v. Krewall, 1969, Okl., 450 P.2d 506 .
We do not believe that Towle’s condition is the result of an occupational disease, which under 39 M.R.S.A. § 183 is defined as follows:
“Whenever used in this law, the term ‘occupational disease’ shall be construed to mean only a disease which is due to causes and conditions which are characteristic of and peculiar to a particular trade, occupation, process or employment and which arises out of and in the course of employment.”
Indeed, there is no evidence in this record that operators of sweepers were more likely to develop diseases of the back gradually caused by their occupation anymore than drivers of tractors, tractor-trailers or other heavy motorized equipment may be. Nor does the record show that all drivers of sweepers are alike constantly exposed to *79 similar strain as befell the petitioner in this case. We cannot say as a matter of law that Towle’s condition is the usual, peculiar or characteristic incident or result of the particular employment in which he was engaged. To the contrary, the cumulative effect of the series of stresses which Towle’s employment caused his back to absorb produced the ultimate disabling injury which was an unintended and unexpected occurrence or accidental injury. American Maize Products Co. v. Nichiporchik, 1940, 108 Ind.App. 502 , 29 N.E.2d 801 .
On appeal from a decree of an Industrial Accident Commissioner the Commissioner’s findings of fact are final if they are supported by competent evidence and reasonable inferences which may be drawn therefrom. 39 M.R.S.A. § 99; Soucy v. Fraser Paper, Limited, 1970, Me., 267 A.2d 919 . Disability due to an industrial accident, the extent thereof, and the issue of causal relation between the accident and the disability are questions of fact, and the compensation claimant has the burden of proof in establishing the same. Baker’s Case, 1947, 143 Me. 103 , 55 A.2d 780 ; MacLeod v. Great Northern Paper Company, 1970, Me., 268 A.2d 488 .
The Commissioner, however, in arriving at his conclusions, must be guided by legal principles and, if he fails in this, he commits an error of law which the Law Court is authorized to correct on appeal. Robitaille’s Case, 1943, 140 Me. 121 , 34 A.2d 473 ; Crosby v. Grandview Nursing Home, 1972, Me., 290 A.2d 375 .
The Commissioner’s decree dismissing the petition is based on his finding that he was “unable to find that the condition [of claimant Towle] resulted from accidental injury.” Since he did find that the condition most probably arose out of and in the course of Mr. Towle’s employment as a sweeper operator, it is obvious that his conclusion there was no proof of an accidental injury was based on the fact which he related in his decree that “no specific incident caused this condition.” In so doing, he misapplied the law, and, as a result thereof, I would sustain the appeal and remand the case to the Commission for the entry of the proper award of compensation.