Tag Archives: SI

Dragging America Into the 20th Century

“?There are two types of nation” a recent Nature editorial begins; “…those that use the metric system and those that have put a man on the Moon.”

Such a pro-American jingoistic statement must be deep British irony. Anyway, the editorial continues …

The reliance of the United States on feet and pounds, along with its refusal to embrace metres and kilograms, baffles outsiders as much as it warms the hearts of some American patriots. But it is time for the country to give up on the curie, the roentgen, the rad and the rem.

This is about measuring radiation. There are several ways of measuring radiation. This has to do with the different ways radiation can exist, and the different kinds of effects it can have. For example, one might want a measure of biological damage, in order to measure, control, document, and discuss exposure in work places or disaster sites. The American tradition for this particular measure is the “rad” but by a 1970s convention that the US apparently ignores, it is the sievert.

The editorial points out the confusion, sometimes meaningful confusion, that arose in the wake of the Fukushima multiple meltdowns, when the Europeans and the Japanese were using sieverts and the Americans all had to pull out their slide rules to convert between sieverts and rads in order to keep track of what was going on. The Nature editorial notes,

Yes, it is possible to use both sets of measures, and to follow the rem numbers with the sievert numbers in brackets. In practice, this is what many US regulatory agencies do. But it is simply too awkward. The Australian government has publicly criticized the US system for creating confusion.

In the middle of an international nuclear-radiation incident, should emergency-response officials huddled in a situation room really need to whip out their calculators?

As I was reading this editorial, I recalled the space robot that essentially crashed into Mars instead of falling into a nice orbit, because the American part of the team was not using the SI (International System of Unites) method of calculating the movement of the robot’s mass. It seems that confusion over units could cause much worse disasters than losing a single (and expensive) robot.

The editors of Nature had the same thought.

Remember NASA’s Mars Climate Orbiter, which was lost in 1999 when someone forgot to convert between imperial and metric units (even though they had plenty of time to check) — the spacecraft broke apart in the Martian atmosphere rather than smoothly entering orbit. Imagine if such an embarrassing error involved the life and safety of millions of people here on Earth.

Clearly, they have a point. The US nuclear industry resists this change because, they say, of cost. However, as Nature argues, it is already the case that the companies that manufacture equipment (and I’d guess software) for use in the nuclear industry already use both units, since they tend to be international.

The US should do this, and should go metric.