As the Great Bonfire War of 2013 continues, we can agree to one thing: If beach fire rings really do generate demonstrably dangerous levels of particulate matter (PM2.5) emissions, they probably need to go or be reduced ("Fire ring hearing may be delayed," April 7).

How much PM2.5 do the fire rings actually generate?

Curiously, that's the one question the South Coast Air Quality Management District (AQMD) seems determined not to answer.

The AQMD's standards provide that an emissions source is significant if it raises particulate concentrations at nearby "sensitive receptors" — residences and similar sites — by at least 2.5 micrograms per square meter (ug/m3). This can easily be measured near the fire rings.

Yet AQMD hasn't done so.

Why? In litigation, there's a rule that when a person has the power to introduce a type of evidence that could be conclusive — but doesn't — it's a reasonable conclusion that the evidence doesn't say what he wants it to say.

AQMD's staff reports simply recite generic studies about health risks from wood smoke generally. Nobody disputes that smoke (like alcohol, peanut butter, sunlight and virtually everything else) can be bad for you at high enough doses. That doesn't mean we ban everything.

A regulatory agency's task is to identify truly significant risks, weigh the costs and benefits and adopt an appropriate response. Agencies generally consider an activity's risk significant if it increases the lifetime risk of harm by one chance in a thousand. Regulations based on speculative or remote harms beyond this threshold may be overturned as arbitrary.

So how do the fire rings affect regional air quality? Their effect is negligible — a rounding error.

Using emissions factors for firewood (that is, the mass of emissions per mass of fuel) taken from peer-reviewed studies, and using reasonable estimates of wood consumption and fire-ring use rates, yields a total figure of about 30 pounds annualized daily average of PM2.5 for all the fire rings in the South Coast basin — about .001% of the 143 tons emitted daily (directly and indirectly) from all sources. By comparison, restaurants charbroiling hamburgers generate several tons of PM2.5 per day.

Using higher-end estimates of a 10% increase in risk for every 10 ug/m3 increase in ambient PM2.5, this translates into a theoretical risk increase of roughly 1 chance in a million. This is not a statistically or epidemiologically significant effect. Even AQMD's own figures, inflated with scientifically obsolete emissions factors and exaggerated assumptions about firewood consumption (three bundles of wood per barbecue?) only suggest an increased risk of 1 in 100,000, still 100 times lower than the significance threshold.

In an ideal world, this analysis would be the end of it. There is no valid reason for singling out beach bonfires for special, drastic treatment. Absent any significant regional health effects, their undisputed benefit to countless people mandates leaving their management to local governments.

Administrative boards like AQMD are well insulated by their structure from accountability to us, the governed. Too often, they become dominated by perpetual insiders; these, in turn, come to see themselves as a caste apart and visibly resent being called to account or justify their decrees.

Some things smell worse than a campfire. Arbitrary government is never good government. AQMD performs a vital public service working to protect air quality. We help it, not hinder it, when we insist it maintain its credibility by basing decisions in sound science.

THOMAS EASTMOND, a Newport Beach resident, practices environmental, regulatory and business law in Irvine.