Abstract
Search of files at Forensic Science SA, Australia, over the past 20 years (1997–2016) revealed three cases of death due to crush asphyxia associated with the use of ride-on lawn mowers. (1) A 61-year-old man was trapped under a ride-on mower that had rolled over. Autopsy examination revealed congestion and petechial haemorrhages of the face and chest, and markings on the chest associated with underlying rib fractures. (2) A 78-year-old man was trapped under a ride-on mower that had also rolled over. Autopsy examination revealed petechial haemorrhages of the face and chest and markings on the chest. (3) A 72-year-old man was found wedged between a ride-on mower and a tree, with petechial haemorrhages of the face and chest, and markings on the front and back of the chest. These cases demonstrate a rare cause of crush asphyxia, often in older males in the domestic environment, which may arise from more than one mechanism.
Introduction
Ride-on lawnmowers are becoming increasingly popular, despite an injury rate of more than three times that of walk-behind mowers. 1 For example, in Ireland, the sales of these mowers increased by 300% between 1996 and 2007. 2 Ride-on mowers are responsible for 10% of all injuries from lawn mowers, with the most severe occurring in children.3,4 This is associated with the mowers’ more complex operation and larger blades and size. 5 The types of injuries that may result from ride-on mowers are often complicated and mutilating, including blade injuries to the feet and hands with amputations of fingers, toes and feet.3,4 Rarely, projectile/missile injuries from any type of mower may occur if an object that has been struck by a rotating blade and launched into the air and impacts a victim. 6
Although injuries from tipping over or from colliding with tree branches have been reported as a hazard for operators of ride-on mowers, 3 fatal cases are rarely reported and usually only in the media. 7 There has also been very little specific documentation of cases, or anything substantive written in the forensic literature on lethal outcomes in these circumstances. For this reason, the following cases taken from the files of Forensic Science SA over the past 20 years (1997–2016) are reported to demonstrate two different situations that may result in lethal asphyxia associated with operating ride-on mowers. All cases had full police and coronial investigations with complete autopsies.
Case reports
Case 1
A 61-year-old man was found dead, face down underneath a ride-on mower that had rolled down an embankment, trapping him beneath.
At autopsy, his eyes were markedly congested with petechiae on the inside of the upper and lower eyelids on the left. There was also marked congestion of the face and upper chest with petechiae of the left upper chest. A series of oblique and intersecting linear red bruises and abrasions were present over the mid-upper back, extending to the top of the left shoulder (the longest mark was approximately 300 mm in length; Figure 1). A parchmented almost horizontal mark was present over the lower mid to left back. Recent fractures of the eighth to eleventh ribs were present posterolaterally on the left side in keeping with chest compression.
Typical markings in crush asphyxia from case 1 who was found dead, face down beneath a ride-on mower. This shows a series of oblique and intersecting linear red bruises and abrasions over the mid-upper back, extending to the top of the left shoulder. These were associated with fractures of the underlying left ribs.
Patchy abrasions were also present over the posterior aspect of the left arm with skin slippage. A linear abrasion with dirt marks measuring 250 mm × 80 mm was present over the anterior lower-right thigh. Scattered abrasions were present over the right knee, the left anterior thigh and the left knee and shin.
Toxicological screening for common drugs was negative, with a low blood alcohol level of 0.011%, possibly related to changes of early putrefaction. There were no significant underlying organic diseases present which could have caused or contributed to death. Death was due to crush asphyxia from entrapment under a ride-on mower, with congestion and petechial haemorrhages of the face and chest, and markings on the chest associated with underlying rib fractures.
Case 2
A 78-year-old man was found dead at the base of a 5 m high embankment under a ride-on mower. The mower appeared to have rolled over on the slope, trapping him beneath. He had a past medical history of hypertension and stroke.
At autopsy, the upper face and scalp were congested, with petechial haemorrhages on the face, scalp, shoulders and conjunctival surfaces of both lower eyelids. Skin markings included a 50 mm ×90 mm bruise in the left posterior axillary line over the lower chest, scattered bruises, abrasions and injuries of the head and hands, with a 30 mm × 120 mm area of discontinuous abrasions/bruising of the upper lateral aspect of the left thigh.
Toxicological screening for alcohol and common drugs was negative, and there were no significant underlying organic diseases present which could have caused or contributed to death. An old lacunar infarct in the right basal ganglia was in keeping with the history of previous stroke. Inspection of the mower found no mechanical problems. Death was due to crush asphyxia from entrapment under a ride-on mower, with petechial haemorrhages of the face and chest, and markings on the chest.
Case 3
A 72-year-old man was found dead, sitting on his ride-on mower wedged between the steering wheel and a tree trunk. It appeared that he had become trapped between the steering wheel and trunk when he had reversed the mower.
At autopsy, petechial haemorrhages were present over the face, anterior neck upper chest and both conjunctivae. Skin markings included a 40 mm area of parchmenting in the centre of the back and a 30 mm × 90 mm area of superficial abrasion in the left inframammary region, in keeping with the history of wedging. There was also a 25 mm × 40 mm abrasion on the lateral aspect of the right elbow.
Other findings included marked native vessel coronary artery atherosclerosis with previous bypass grafting in good order, and evidence of previous abdominal surgery with scattered fibrous adhesions. No alcohol was detected in the blood, and there were no other organic diseases present which could have caused or contributed to death. Death was due to crush asphyxia from being wedged between a ride-on mower and a tree, with petechial haemorrhages of the face and chest, and markings on front and back of the chest. This case was previously listed in an audit of 79 cases of crush asphyxia between 1980 and 2004 in South Australia. 8
Discussion
Mower rollovers are potentially quite dangerous events, with studies showing that in 75% of cases, the operator ends up underneath the machine. 1 This clearly carries a significant risk of crush asphyxia if the chest is compressed or the diaphragm splinted. Rollovers occur when mowers are being driven on inclines or at speed 5 and may occur very rapidly. For example, it has been estimated that a mower may roll completely within 1.5 s. This gives very little time for evasive action, thus casting doubt on the validity of suggestions by manufacturers that operator protection is not required if drivers jump quickly off an overturning vehicle. In addition, although it has been proposed that operators should not operate on inclines of >15°, it has been shown that making this assessment accurately purely by observation is often very difficult. 1 To date, deaths from ride-on mowers have been associated with rollovers, run overs and falls, with run overs predominately involving children.4,5
Crush asphyxia refers to a situation where respiratory effort is prevented by compression of the torso, resulting in characteristic pathological findings of marked swelling and congestion of the face with extensive petechial haemorrhages of the face neck and conjunctivae. There may be bleeding from the nose and ears, and intense congestion of the thyroid gland producing a black colour, with blood lakes on histology.8,9 Rarely, lethal asphyxia may occur in motor vehicle accidents predisposed to by drug or alcohol intoxication, obesity or blunt trauma, and usually involving rollovers. 10 Crush asphyxia may also occur if a driver becomes trapped between the door of a still-moving vehicle and a stationary object.11,12
All three of the reported cases showed clear pathological evidence of crush asphyxia with extensive facial, conjunctival and upper body petechaie and markings on the chests and bodies consistent with the described incidents. In cases 1 and 2, death had resulted from the victims being pinned under mowers that had rolled over. In the third case, the mechanism of death was slightly more unusual, with the operator becoming trapped between the steering wheel and a tree trunk when he had reversed the mower. It is interesting to note that the highest rates of lawn mower injuries have been found in males aged >60 years, 5 and in the present series, all decedents were males with an age range of 61–78 years (average 70 years). It has been suggested that less robust older males are at greater risk of injury than younger individuals, and that they may favour ride-on mowers, as they are less able to cope with walk-behind (push) mowers 5 . Males are also more likely to look after lawn mowing in the domestic situation, although this is clearly not always the case. 7 In conclusion, this study has presented a rare cause of crush asphyxia in the domestic environment that may arise from more than one mechanism. Older males may be at particular risk.
Footnotes
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.
Funding
This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.