Keeping the ice ready is the engineers’ game

by Rob Lee

Two hockey teams hit the ice, greeted by the cheers of 15,000-plus fans on game nights at Toronto’s Maple Leaf Gardens (MLG).

But those fans might well reserve some of their applause for a third team, which conducts its pre-game preparations in the engineering room. That team is the MLG operating engineers, and it’s their job to make sure the fans’ hockey heroes are provided with the best sheet of ice possible.

This third team’s mandate is to create and hold roughly 16,500 square feet of three-quarter inch thick ice, making sure it’s hard and level enough to allow the pro hockey show to go on two and sometimes three nights a week during the seven-month National Hockey League season.


Chief engineer Forbes (Mitch) Mitchell takes pressure readings in the MLG mechanical room. Mitch keeps an engineer on duty 24 hours a day during hockey season. He arrived at the Gardens in 1977.

The six man engineering team is headed by Forbes “Mitch” Mitchell, a first-class stationary engineer who has been plying his trade at MLG for 16 years, the past six as chief engineer. Mitch was introduced to engineering during stints on various trawlers in his native Scotland. After coming to Canada, he spent several years at Sealtest Dairies, before finally finding his way to the Gardens. In total, Mitch has 30 years experience in the industry. He is only the fourth chief engineer in Gardens’ history.

Mitch’s team toils under the bowl (seating) at MLG, monitoring the refrigeration system 24 hours a day. “They’re even busier during a game,” says Wayne Gillespie, MLG building manager. “They’re always doing checks on pressures, temperatures, everything… all the time.”

Compressor suction and discharge pressure readings have been faithfully supplied by these Linde gauges from the day the Gardens opened.


The freezing of the ice sheet is accomplished by the circulation of 30,000 gallons of brine (calcium chloride) as the secondary refrigerant, pumped through 296 one inch diameter plastic pipes set in parallel rows on 3.5″ centres embedded in concrete below the ice surface. Using ammonia as the primary refrigerant and a total available compressor capacity of 300 tons (two 200 HP compressors and two 100 HP units), the brine is cooled to a temperature of between 0 and 5 degrees Fahrenheit and pumped at 20 psi through a 100-yard tunnel from the compressor room, via 8″ lines, to below the ice surface. The 296 one inch pipes run lengthwise off the 6″ supply and return headers. This design ensures the ice sheet holds at a temperature of between 15 deg. F. and 17 deg. F. still using original equipment.


THE MONSTER OF THE MECHANICAL ROOM: It’s old, but it just keeps working. This 100 HP is the last of the 1931-installed compressors. The mechanical room has three other units: another 100 HP and two 200 HP.

Perhaps the most amazing aspect of the ice making process at MLG is the fact that the engineering crew is still using some of the building’s original equipment. One of the 100HP compressors, a number of temperature gauges, a brine pump and the cork-insulated brine tank have been in operation since Day One, November 1931.

Mitch recalls when there was talk about replacing the old compressor, but the late Harold Ballard, who owned the Gardens at the time, wouldn’t hear of it. “He came in, and said `that one stays’. There was no need to replace it, because it was working fine”. In fact, most the old equipment continues to perform without fault.

Hockey players are not the only people who put demands on the icemakers at MLG. Mitch has to occasionally meet the requirements of figure skaters as well, who like softer ice, almost to the wet stage. This is accomplished by raising the ice temperature roughly four degrees F., resulting in a softer surface. This allows them to clearly see the tracings of their skates and to cushion the impact of their triple jumps.

Mitch is able to make these pinpoint differentials through a series of temperature probes embedded throughout the ice slab. (There are also two probes under the ice, below the insulation, to indicate if the permafrost is getting too deep.)

To achieve the desired temperatures, an average brine temperature about two to three degrees F. lower than the required ice temperature is sufficient. Of course, where abnormally high loads are experienced, the temperature of the brine must be lowered to maintain the same ice conditions.

The Garden’s ice is installed in late August or early September, in time for Leaf training camp. When the plant is first placed in operation, the refrigeration equipment is operated long enough for a sharp frost to appear on the concrete surface.


Modern ice surfacing equipment

“What we do is pull the brine temperature down first,” explains Mitch, “before we start putting the ice in. And we pull the floor right down, to about 17 degrees. The ice crew will then go out and pebble it. and that will put a seal on the floor. Then we build it up about a quarter of an inch, and paint it.”


Ice resurfacing equipment used at MLG into the 1950s is now retired and on permanent display in the Gardens’ foyer.

By painting the ice white (below the finished surface to not interfere with skating and resurfacing operations) the radiant heat gain is reduced considerably, as well as improving the visual contrast, which is critical for a good television broadcast. The paint used at MLG has a metal oxide base and is supplied by Jet Ice of Richmond Hill, Ontario. Also at this stage, the Maple Leaf logo, the centre, blue and goal lines, faceoff circles and goal creases are applied with templates. Additional layers are then built up. “We don’t want to go over three-quarters of an inch if we can help it,” Mitch adds. `We go thicker when we have an ice show coming in.”

To maintain the surface, the accumulated snow and shavings are scraped off after each hockey period or figure skating session, and a new ice surface (using warm water) is layed down. The warm water generally results in harder ice since air bubbles are removed. The Gardens uses deionized water from a Jet Ice system.

According to engineer Doug Lowther, the type of water used is important. “Deionized water is free of impurities”.

Visitors to the Gardens marvel at the history of the old place: the ancient photos in the foyer, and the Stanley Cup banners hanging from the rafters. But for some understandable reason, the ice surface is what everyone wants to see. And Wayne occasionally complies, when time allows him. He has been known to take a tourist on an impromptu spin of the bowl, always ending at rink side with an invitation to walk onto the surface.

“It’s amazing. I’ll take them down to the ice, and let them step out, and they can’t believe they’re standing on it. I mean it’s ice, it’s just ice. But to them, it’s incredible”.

Rob Lee is a Toronto-based free lance writer and a former apprentice refrigeration mechanic.

Reproduced by permission of Heating, Plumbing and Air Conditioning, February 1993